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Sample records for comb swept lasers

  1. Frequency characterization of a swept- and fixed-wavelength external-cavity quantum cascade laser by use of a frequency comb.

    PubMed

    Knabe, Kevin; Williams, Paul A; Giorgetta, Fabrizio R; Armacost, Chris M; Crivello, Sam; Radunsky, Michael B; Newbury, Nathan R

    2012-05-21

    The instantaneous optical frequency of an external-cavity quantum cascade laser (QCL) is characterized by comparison to a near-infrared frequency comb. Fluctuations in the instantaneous optical frequency are analyzed to determine the frequency-noise power spectral density for the external-cavity QCL both during fixed-wavelength and swept-wavelength operation. The noise performance of a near-infrared external-cavity diode laser is measured for comparison. In addition to providing basic frequency metrology of external-cavity QCLs, this comb-calibrated swept QCL system can be applied to rapid, precise broadband spectroscopy in the mid-infrared spectral region. PMID:22714230

  2. Tuning of successively scanned two monolithic Vernier-tuned lasers and selective data sampling in optical comb swept source optical coherence tomography

    PubMed Central

    Choi, Dong-hak; Yoshimura, Reiko; Ohbayashi, Kohji

    2013-01-01

    Monolithic Vernier tuned super-structure grating distributed Bragg reflector (SSG-DBR) lasers are expected to become one of the most promising sources for swept source optical coherence tomography (SS-OCT) with a long coherence length, reduced sensitivity roll-off, and potential capability for a very fast A-scan rate. However, previous implementations of the lasers suffer from four main problems: 1) frequencies deviate from the targeted values when scanned, 2) large amounts of noise appear associated with abrupt changes in injection currents, 3) optically aliased noise appears due to a long coherence length, and 4) the narrow wavelength coverage of a single chip limits resolution. We have developed a method of dynamical frequency tuning, a method of selective data sampling to eliminate current switching noise, an interferometer to reduce aliased noise, and an excess-noise-free connection of two serially scanned lasers to enhance resolution to solve these problems. An optical frequency comb SS-OCT system was achieved with a sensitivity of 124 dB and a dynamic range of 55-72 dB that depended on the depth at an A-scan rate of 3.1 kHz with a resolution of 15 μm by discretely scanning two SSG-DBR lasers, i.e., L-band (1.560-1.599 μm) and UL-band (1.598-1.640 μm). A few OCT images with excellent image penetration depth were obtained. PMID:24409394

  3. Wavelength Swept Lasers

    NASA Astrophysics Data System (ADS)

    Yun, Seok Hyun; Bouma, Brett E.

    In optical interferometric metrology, the wavelength of light serves as a reference for length. At a given optical wavelength, an interference signal varies as a sinusoidal function of distance with a period equal to the wavelength. Although this approach offers unrivaled precision, the periodic signal results in a 2π ambiguity for measurement of lengths greater than one wavelength. In optical coherence tomography (OCT), one wishes to determine light scattering distances and distribution within a sample, but without the ambiguity. To accomplish this, OCT is based on interferometry using many optical wavelengths, each serving as a "ruler" with different periodicities. OCT traditionally has used broadband light sources providing a wide range of wavelengths, all simultaneously. Alternatively, a tunable light source emitting one wavelength at a time, rapidly swept over a broad spectral range, can also be used to achieve the absolute ranging capability in OCT. In this chapter, we describe a technical overview of these new emerging sources. We begin with a discussion general specifications of these light sources, the review basic fundamentals of laser and wavelength tuning. Finally, we discuss the principles of various techniques developed to date for high-speed and wide tuning range.

  4. Swept Frequency Laser Metrology System

    NASA Technical Reports Server (NTRS)

    Zhao, Feng (Inventor)

    2010-01-01

    A swept frequency laser ranging system having sub-micron accuracy that employs multiple common-path heterodyne interferometers, one coupled to a calibrated delay-line for use as an absolute reference for the ranging system. An exemplary embodiment uses two laser heterodyne interferometers to create two laser beams at two different frequencies to measure distance and motions of target(s). Heterodyne fringes generated from reflections off a reference fiducial X(sub R) and measurement (or target) fiducial X(sub M) are reflected back and are then detected by photodiodes. The measured phase changes Delta phi(sub R) and Delta phi (sub m) resulting from the laser frequency swept gives target position. The reference delay-line is the only absolute reference needed in the metrology system and this provides an ultra-stable reference and simple/economical system.

  5. Laser Spectroscopy and Frequency Combs

    NASA Astrophysics Data System (ADS)

    Hänsch, Theodor W.; Picqué, Nathalie

    2013-12-01

    The spectrum of a frequency comb, commonly generated by a mode-locked femtosecond laser consists of several hundred thousand precisely evenly spaced spectral lines. Such laser frequency combs have revolutionized the art measuring the frequency of light, and they provide the long-missing clockwork for optical atomic clocks. The invention of the frequency comb technique has been motivated by precision laser spectroscopy of the simple hydrogen atom. The availability of commercial instruments is facilitating the evolution of new applications far beyond the original purpose. Laser combs are becoming powerful instruments for broadband molecular spectroscopy by dramatically improving the resolution and recording speed of Fourier spectrometers and by creating new opportunities for highly multiplexed nonlinear spectroscopy, such as two-photon spectroscopy or coherent Raman spectroscopy. Other emerging applications of frequency combs range from fundamental research in astronomy, chemistry, or attosecond science to telecommunications and satellite navigation.

  6. Spectrally interleaved, comb-mode-resolved spectroscopy using swept dual terahertz combs

    PubMed Central

    Hsieh, Yi-Da; Iyonaga, Yuki; Sakaguchi, Yoshiyuki; Yokoyama, Shuko; Inaba, Hajime; Minoshima, Kaoru; Hindle, Francis; Araki, Tsutomu; Yasui, Takeshi

    2014-01-01

    Optical frequency combs are innovative tools for broadband spectroscopy because a series of comb modes can serve as frequency markers that are traceable to a microwave frequency standard. However, a mode distribution that is too discrete limits the spectral sampling interval to the mode frequency spacing even though individual mode linewidth is sufficiently narrow. Here, using a combination of a spectral interleaving and dual-comb spectroscopy in the terahertz (THz) region, we achieved a spectral sampling interval equal to the mode linewidth rather than the mode spacing. The spectrally interleaved THz comb was realized by sweeping the laser repetition frequency and interleaving additional frequency marks. In low-pressure gas spectroscopy, we achieved an improved spectral sampling density of 2.5 MHz and enhanced spectral accuracy of 8.39 × 10−7 in the THz region. The proposed method is a powerful tool for simultaneously achieving high resolution, high accuracy, and broad spectral coverage in THz spectroscopy. PMID:24448604

  7. SNR of swept SLEDs and swept lasers for OCT.

    PubMed

    Johnson, Bart; Atia, Walid; Flanders, Dale C; Kuznetsov, Mark; Goldberg, Brian D; Kemp, Nate; Whitney, Peter

    2016-05-16

    A back-to-back comparison of a tunable narrow-band-filtered SLED (TSLED) and a swept laser are made for OCT applications. The two sources are similar in terms of sweep speed, tuning range and coherence length. A fundamental issue with a TSLED is that the RIN is proportional to 1/linewidth, meaning that the longer the coherence length, the higher the RIN and clock jitter. We show that the TSLED has an SNR limit that causes noise streaks at points of high reflection in images. The laser, which is shot noise limited, does not exhibit this effect. We add noise terms proportional to the sample power times reference power to standard swept source SNR expressions to account for the SNR limit. PMID:27409939

  8. Quantum Cascade Laser Frequency Combs

    NASA Astrophysics Data System (ADS)

    Faist, Jérôme; Villares, Gustavo; Scalari, Giacomo; Rösch, Markus; Bonzon, Christopher; Hugi, Andreas; Beck, Mattias

    2016-06-01

    It was recently demonstrated that broadband quantum cascade lasers can operate as frequency combs. As such, they operate under direct electrical pumping at both mid-infrared and THz frequencies, making them very attractive for dual-comb spectroscopy. Performance levels are continuously improving, with average powers over 100mW and frequency coverage of 100 cm-1 in the mid-infrared region. In the THz range, 10mW of average power and 600 GHz of frequency coverage are reported. As a result of the very short upper state lifetime of the gain medium, the mode proliferation in these sources arises from four-wave mixing rather than saturable absorption. As a result, their optical output is characterized by the tendency of small intensity modulation of the output power, and the relative phases of the modes to be similar to the ones of a frequency modulated laser. Recent results include the proof of comb operation down to a metrological level, the observation of a Schawlow-Townes broadened linewidth, as well as the first dual-comb spectroscopy measurements. The capability of the structure to integrate monothically nonlinear optical elements as well as to operate as a detector shows great promise for future chip integration of dual-comb systems.

  9. Monolithically integrated absolute frequency comb laser system

    DOEpatents

    Wanke, Michael C.

    2016-07-12

    Rather than down-convert optical frequencies, a QCL laser system directly generates a THz frequency comb in a compact monolithically integrated chip that can be locked to an absolute frequency without the need of a frequency-comb synthesizer. The monolithic, absolute frequency comb can provide a THz frequency reference and tool for high-resolution broad band spectroscopy.

  10. Coherent Raman spectro-imaging with laser frequency combs.

    PubMed

    Ideguchi, Takuro; Holzner, Simon; Bernhardt, Birgitta; Guelachvili, Guy; Picqué, Nathalie; Hänsch, Theodor W

    2013-10-17

    Advances in optical spectroscopy and microscopy have had a profound impact throughout the physical, chemical and biological sciences. One example is coherent Raman spectroscopy, a versatile technique interrogating vibrational transitions in molecules. It offers high spatial resolution and three-dimensional sectioning capabilities that make it a label-free tool for the non-destructive and chemically selective probing of complex systems. Indeed, single-colour Raman bands have been imaged in biological tissue at video rates by using ultra-short-pulse lasers. However, identifying multiple, and possibly unknown, molecules requires broad spectral bandwidth and high resolution. Moderate spectral spans combined with high-speed acquisition are now within reach using multichannel detection or frequency-swept laser beams. Laser frequency combs are finding increasing use for broadband molecular linear absorption spectroscopy. Here we show, by exploring their potential for nonlinear spectroscopy, that they can be harnessed for coherent anti-Stokes Raman spectroscopy and spectro-imaging. The method uses two combs and can simultaneously measure, on the microsecond timescale, all spectral elements over a wide bandwidth and with high resolution on a single photodetector. Although the overall measurement time in our proof-of-principle experiments is limited by the waiting times between successive spectral acquisitions, this limitation can be overcome with further system development. We therefore expect that our approach of using laser frequency combs will not only enable new applications for nonlinear microscopy but also benefit other nonlinear spectroscopic techniques. PMID:24132293

  11. On-chip dual-comb based on quantum cascade laser frequency combs

    SciTech Connect

    Villares, G. Wolf, J.; Kazakov, D.; Süess, M. J.; Beck, M.; Faist, J.; Hugi, A.

    2015-12-21

    Dual-comb spectroscopy is emerging as an appealing application of mid-infrared frequency combs for high-resolution molecular spectroscopy, as it leverages on the unique coherence properties of frequency combs. Here, we present an on-chip dual-comb source based on mid-infrared quantum cascade laser frequency combs. Control of the combs repetition and offset frequencies is obtained by integrating micro-heaters next to each laser. We show that a full control of the dual-comb system is possible, by measuring a multi-heterodyne beating corresponding to an optical bandwidth of 32 cm{sup −1} centered at 1330 cm{sup −1} (7.52 μm), demonstrating that this device represents a critical step towards compact dual-comb systems.

  12. Spectroscopy with Comb-Referenced Diode Lasers

    NASA Astrophysics Data System (ADS)

    Cich, Matthew; Lopez, Gary V.; Johnson, Philip M.; Sears, Trevor J.; McRaven, Christopher P.

    2010-06-01

    Extended cavity diode lasers have been stabilized by locking to components of an erbium-doped fiber laser-based frequency comb with a 250 MHz comb spacing centered at 1.5μ m. We find the Allan variance of the diode laser frequency relative to the single comb component to which it is locked is of the order of a few Hz. For the system as a whole, the absolute frequency accuracy is approximately 1.5 parts in 1012. In order to characterize the system more completely, we have recorded saturation dip absorption spectra of several transitions in the ν_1 + ν_3 combination band of acetylene near 6530 cm-1. We find good agreement with published absolute frequency measurements for these transitions, which have been used as secondary frequency standards in the past. Aside from extremely precise saturation dip measurements such as these, comb-stabilized lasers should permit excellent measurements of Doppler-broadened lineshapes, both to compare with theory and for analytical applications. Progress along these lines will be reported at the meeting. Acknowledgments: T. J. Sears gratefully acknowledges support from a Brookhaven National Laboratory program development grant that enabled this work and also support for research at Brookhaven National Laboratory which was carried out under Contract No. DE-AC02-98CH10886 with the U.S. Department of Energy and supported by its Office of Basic Energy Sciences, Division of Chemical Sciences, Geosciences and Biosciences.

  13. Diffuse optical tomography using wavelength-swept laser

    NASA Astrophysics Data System (ADS)

    Cho, Jaedu; Lim, Gukbin; Jeong, Myung Yung; Nalcioglu, Orhan; Kim, Chang-Seok; Gulsen, Gultekin

    2013-03-01

    The design and implementation of a diffuse optical tomography system using wavelength-swept laser is described. Rapid and continuous wavelength change is utilized for high speed spectral scanning from 775 nm to 875 nm optical wavelength. Maximum speed of wavelength repetition is 1 kHz and averaged output power of the wavelength-swept laser is 20 mW. A fiber-optic Sagnac interferometer is incorporated to conduct passive amplitude modulation of the wavelength-swept laser. It is shown that the wavelength-swept laser can be successfully incorporated to the DOT system, and then reduces wavelength-shifting time and hardware complexity in multi-wavelength DOT implementation.

  14. Optical Frequency Comb Generation based on Erbium Fiber Lasers

    NASA Astrophysics Data System (ADS)

    Droste, Stefan; Ycas, Gabriel; Washburn, Brian R.; Coddington, Ian; Newbury, Nathan R.

    2016-06-01

    Optical frequency combs have revolutionized optical frequency metrology and are being actively investigated in a number of applications outside of pure optical frequency metrology. For reasons of cost, robustness, performance, and flexibility, the erbium fiber laser frequency comb has emerged as the most commonly used frequency comb system and many different designs of erbium fiber frequency combs have been demonstrated. We review the different approaches taken in the design of erbium fiber frequency combs, including the major building blocks of the underlying mode-locked laser, amplifier, supercontinuum generation and actuators for stabilization of the frequency comb.

  15. Fully referenced single-comb interferometry using optical sampling by laser-cavity tuning.

    PubMed

    Potvin, Simon; Boudreau, Sylvain; Deschênes, Jean-Daniel; Genest, Jérôme

    2013-01-10

    The correction of setup and laser instabilities in a single-comb interferometric measurement using optical sampling by laser-cavity tuning is investigated. A two-reference solution that allows full correction of the interferogram is presented. The technique is compared to a slightly simpler one-reference correction. For the one-reference case, all the subtleties involved in this partial correction and the dependence between the achievable measurement accuracy and the setup parameters are highlighted. The parameters considered are the comb bandwidth, the laser-frequency noise, the required spectral resolution, the cavity scan speed, and the length of the delay line. For both referencing approaches, experimental results using a fiber delay line of 10 km and a 100 MHz mode-locked laser with its repetition rate swept at 500 Hz are shown. PMID:23314642

  16. FBG interrogation method based on wavelength-swept laser

    NASA Astrophysics Data System (ADS)

    Qin, Chuan; Zhao, Jianlin; Jiang, Biqiang; Rauf, Abdul; Wang, Donghui; Yang, Dexing

    2013-06-01

    Wavelength-swept laser technique is an active demodulation method which integrates laser source and detecting circuit together to achieve compact size. The method also has the advantages such as large demodulation range, high accuracy, and comparatively high speed. In this paper, we present a FBG interrogation method based on wavelength-swept Laser, in which an erbium-doped fiber is used as gain medium and connected by a WDM to form a ring cavity, a fiber FP tunable filter is inserted in the loop for choosing the laser frequency and a gas absorption cell is adopted as a frequency reference. The laser wavelength is swept by driving the FP filter. If the laser wavelength matches with that of FBG sensors, there will be some strong reflection peak signals. Detecting such signals with the transmittance signal after the gas absorption cell synchronously and analyzing them, the center wavelengths of the FBG sensors are calculated out at last. Here, we discuss the data processing method based on the frequency reference, and experimentally study the swept laser characteristics. Finally, we adopt this interrogator to demodulate FBG stress sensors. The results show that, the demodulation range almost covers C+L band, the resolution and accuracy can reach about 1pm or less and 5pm respectively. So it is very suitable for most FBG measurements.

  17. Microresonator-based comb generation without an external laser source.

    PubMed

    Johnson, Adrea R; Okawachi, Yoshitomo; Lamont, Michael R E; Levy, Jacob S; Lipson, Michal; Gaeta, Alexander L

    2014-01-27

    We demonstrate a fiber-microresonator dual-cavity architecture with which we generate 880 nm of comb bandwidth without the need for a continuous-wave pump laser. Comb generation with this pumping scheme is greatly simplified as compared to pumping with a single frequency laser, and the generated combs are inherently robust due to the intrinsic feedback mechanism. Temporal and radio frequency (RF) characterization show a regime of steady comb formation that operates with reduced RF amplitude noise. The dual-cavity design is capable of being integrated on-chip and offers the potential of a turn-key broadband multiple wavelength source. PMID:24515147

  18. SLEDs and Swept Source Laser Technology for OCT

    NASA Astrophysics Data System (ADS)

    Duelk, Marcus; Hsu, Kevin

    EXALOS offers broadband and high-power superluminescent light-emitting diodes (SLEDs) and high-speed wavelength-swept lasers, covering various visible and near-infrared wavelength regions (390-1,700 nm). These diverse wavelengths are realized in different semiconductor material systems such as GaN, GaAs, or InP. Those light sources are used in various fields such as navigation, optical coherence tomography (OCT), metrology, sensing, and microscopy. Detailed discussions on SLED characteristics and key swept-source OCT system design parameters are presented.

  19. Stabilization of femtosecond laser frequency combs with subhertz residual linewidths.

    PubMed

    Bartels, A; Oates, C W; Hollberg, L; Diddams, S A

    2004-05-15

    We demonstrate that femtosecond laser frequency combs (FLFCs) can have a subhertz linewidth across their entire emission spectra when they are phase locked to a reference laser with a similarly narrow linewidth. Correspondingly, the coherence time of the comb components relative to the reference laser can be of the order of a few seconds. Thus we are able to detect high-contrast spectral interferograms at up to 10-s integration time between two FLFCs locked to a common optical reference. PMID:15181992

  20. Dual-comb spectroscopy based on quantum-cascade-laser frequency combs.

    PubMed

    Villares, Gustavo; Hugi, Andreas; Blaser, Stéphane; Faist, Jérôme

    2014-01-01

    Dual-comb spectroscopy performed in the mid-infrared-where molecules have their strongest rotovibrational absorption lines-offers the promise of high spectral resolution broadband spectroscopy with very short acquisition times (μs) and no moving parts. Recently, we demonstrated frequency comb operation of a quantum-cascade-laser. We now use that device in a compact, dual-comb spectrometer. The noise properties of the heterodyne beat are close to the shot noise limit. Broadband (15 cm(-1)) high-resolution (80 MHz) absorption spectroscopy of both a GaAs etalon and water vapour is demonstrated, showing the potential of quantum-cascade-laser frequency combs as the basis for a compact, all solid-state, broadband chemical sensor. PMID:25307936

  1. SNR of swept SLEDs and swept lasers for OCT (Conference Presentation)

    NASA Astrophysics Data System (ADS)

    Johnson, Bart C.; Atia, Walid; Flanders, Dale; Kuznetsov, Mark; Goldberg, Brian; Kemp, Nate; Whitney, Peter

    2016-03-01

    A back-to-back comparison of a tunable narrow-band SLED (TSLED) and a swept laser are made for OCT applications. Both are 1310 nm sources sweeping at 50 kHz over a 100 nm tuning range and have similar coherence lengths. The TSLED consists of a seed SOA and two amplification SOAs. The ASE is filtered twice by a tunable MEMS Fabry Perot in a polarization multiplexed double-pass arrangement on either side of the middle SOA. This allows very long coherence lengths to be achieved. A fundamental issue with a SLED is that the RIN is proportional to 1/Linewidth, meaning that the longer the coherence length, the higher the RIN. High RIN also leads to increased clock jitter. Most swept source SNR calculations assume that the noise is independent of the amplitude of the signal light: The higher the signal, the higher the SNR. We show that in the case of the TSLED, that the high signal RIN and clock jitter give rise to additional noises that scale with signal power. This leads to an SNR limit in the case of the TSLED: The higher the signal, the higher the noise, so the SNR reaches a limit. While the TSLED has respectable sensitivity, the SNR limit causes noise streaks in an image where the A-line has a high reflectivity point. The laser, which is shot noise limited, does not exhibit this effect. This is illustrated with SNR data and side-by-side images taken with the two sources.

  2. Characterization of FBG sensor interrogation based on a FDML wavelength swept laser

    PubMed Central

    Jung, Eun Joo; Kim, Chang-Seok; Jeong, Myung Yung; Kim, Moon Ki; Jeon, Min Yong; Jung, Woonggyu; Chen, Zhongping

    2012-01-01

    In this study, we develop an ultra-fast fiber Bragg grating sensor system that is based on the Fourier domain mode-locked (FDML) swept laser. A FDML wavelength swept laser has many advantages compared to the conventional wavelength swept laser source, such as high-speed interrogation, narrow spectral sensitivity, and high phase stability. The newly developed FDML wavelength swept laser shows a superior performance of a high scan rate of 31.3 kHz and a broad scan range of over 70 nm simultaneously. The performance of the grating sensor interrogating system using a FDML wavelength swept laser is characterized in both static and dynamic strain responses. PMID:18852764

  3. Quantum cascade laser combs: effects of modulation and dispersion.

    PubMed

    Villares, Gustavo; Faist, Jérôme

    2015-01-26

    Frequency comb formation in quantum cascade lasers is studied theoretically using a Maxwell-Bloch formalism based on a modal decomposition, where dispersion is considered. In the mid-infrared, comb formation persists in the presence of weak cavity dispersion (500 fs2 mm-1) but disappears when much larger values are used (30'000 fs2 mm-1). Active modulation at the round-trip frequency is found to induce mode-locking in THz devices, where the upper state lifetime is in the tens of picoseconds. Our results show that mode-locking based on four-wave mixing in broadband gain, low dispersion cavities is the most promising way of achieving broadband quantum cascade laser frequency combs. PMID:25835922

  4. Laser frequency comb techniques for precise astronomical spectroscopy

    NASA Astrophysics Data System (ADS)

    Murphy, Michael T.; Locke, Clayton R.; Light, Philip S.; Luiten, Andre N.; Lawrence, Jon S.

    2012-05-01

    Precise astronomical spectroscopic analyses routinely assume that individual pixels in charge-coupled devices (CCDs) have uniform sensitivity to photons. Intra-pixel sensitivity (IPS) variations may already cause small systematic errors in, for example, studies of extra-solar planets via stellar radial velocities and cosmological variability in fundamental constants via quasar spectroscopy, but future experiments requiring velocity precisions approaching ˜1 cm s-1 will be more strongly affected. Laser frequency combs have been shown to provide highly precise wavelength calibration for astronomical spectrographs, but here we show that they can also be used to measure IPS variations in astronomical CCDs in situ. We successfully tested a laser frequency comb system on the Ultra-High-Resolution Facility spectrograph at the Anglo-Australian Telescope. By modelling the two-dimensional comb signal recorded in a single CCD exposure, we find that the average IPS deviates by <8 per cent if it is assumed to vary symmetrically about the pixel centre. We also demonstrate that a series of comb exposures with absolutely known offsets between them can yield tighter constraints on symmetric IPS variations from ˜100 pixels. We discuss measurement of asymmetric IPS variations and absolute wavelength calibration of astronomical spectrographs and CCDs using frequency combs.

  5. Development of fast FBG interrogator with wavelength-swept laser

    NASA Astrophysics Data System (ADS)

    Yamaguchi, Tatsuya; Shinoda, Yukitaka

    2015-05-01

    The objective of this research is the construction of a structural health monitoring system that uses fiber Bragg grating (FBG) to determine the health of structures. We develop fast FBG interrogator for real-time measurement of the reflected wavelength of a multipoint FBG to monitor the broadband vibration of a structure. This FBG interrogator, which combines a wavelength-swept laser and a real-time measurement system is capable of measuring wavelength within a standard deviation of 2×10-3 nm or less. We have demonstrated that the FBG interrogator is able to measure vibration that has a resonance frequency of 440 Hz at intervals of 0.1 ms with a multipoint FBG.

  6. Coherent combs in ionization by intense and short laser pulses

    NASA Astrophysics Data System (ADS)

    Krajewska, K.; Kamiński, J. Z.

    2016-03-01

    Photoionization of positive ions by a train of intense, short laser pulses is investigated within the relativistic strong field approximation, using the velocity gauge. The formation of broad peak structures in the high-energy domain of photoelectrons is observed and interpreted. The emergence of coherent photoelectron energy combs within these structures is demonstrated, and it is interpreted as the consequence of the Fraunhofer-type interference/diffraction of probability amplitudes of ionization from individual pulses comprising the train. Extensions to the coherent angular combs are also studied, and effects related to the radiation pressure are presented.

  7. Wideband Raman-Pumped Wavelength-Swept Laser for Optical Coherence Tomography Application

    NASA Astrophysics Data System (ADS)

    Xu, Jianbing; Ou, Haiyan; Xu, Xing; Yang, Victor Xiao Dong; Chui, Po Ching; Kin-Yip Wong, Kenneth

    2013-06-01

    We demonstrate a new wavelength-swept laser based on fiber Raman amplification (FRA), achieved by multiplexing three different pump lasers at wavelengths of 1455, 1475, and 1509 nm. The obtained sweeping bandwidth was from 1526.1 to 1637.9 nm, which was as wide as 111.8 nm. It is the widest hitherto demonstrated based on FRA. We also present the use of this swept laser in the application scenario of optical coherence tomography (OCT). This scheme paves the way for fiber Raman amplification to be employed as a promising source for generating a wideband swept source for OCT application.

  8. Progress Report on a Portable TI:SAPPHIRE Comb Laser with Frequencies Referring to Cesium Atom Two-Photon Transitions

    NASA Astrophysics Data System (ADS)

    Cheng, Wang-Yau; Wu, Chien-Ming; Liu, Tz-Wei; Chen, Yo-Huan

    2010-06-01

    A portable Ti:sapphire comb laser would contribute significantly to generalize comb-laser applications, such as the astro-comb missions or other interdisciplinary collaborations. To develop a portable comb laser, three barriers lie ahead: one is to miniaturize and robotize the frequency reference system of the comb laser; the second is to ensure the long-term frequency accuracy without satellite connection, and the third is to miniaturize the pumping laser system. We developed two hand-size cesium-stabilized diode lasers at 822 nm and 884 nm to serve as frequency references for a comb laser and we carried out a comb-laser-based CPT experiment with one single cesium cell that might offer a locking procedure for long-term comb laser accuracy. We will also report our plans and progress on a fiber laser pumped Ti:sapphire comb laser.

  9. Extended-Cavity Semiconductor Wavelength-Swept Laser for Biomedical Imaging

    PubMed Central

    Yun, S. H.; Boudoux, C.; Pierce, M. C.; de Boer, J. F.; Tearney, G. J.; Bouma, B. E.

    2010-01-01

    We demonstrate a compact high-power rapidly swept wavelength tunable laser source based on a semiconductor optical amplifier and an extended-cavity grating filter. The laser produces excellent output characteristics for biomedical imaging, exhibiting >4-mW average output power, <0.06-nm instantaneous linewidth, and >80-dB noise extinction with its center wavelength swept over 100 nm at 1310 nm at variable repetition rates up to 500 Hz. PMID:20640193

  10. Target micro-displacement measurement by a "comb" structure of intensity distribution in laser plasma propulsion

    NASA Astrophysics Data System (ADS)

    Zheng, Z. Y.; Zhang, S. Q.; Gao, L.; Gao, H.

    2015-05-01

    A "comb" structure of beam intensity distribution is designed and achieved to measure a target displacement of micrometer level in laser plasma propulsion. Base on the "comb" structure, the target displacement generated by nanosecond laser ablation solid target is measured and discussed. It is found that the "comb" structure is more suitable for a thin film target with a velocity lower than tens of millimeters per second. Combing with a light-electric monitor, the `comb' structure can be used to measure a large range velocity.

  11. Active laser ranging with frequency transfer using frequency comb

    NASA Astrophysics Data System (ADS)

    Zhang, Hongyuan; Wei, Haoyun; Yang, Honglei; Li, Yan

    2016-05-01

    A comb-based active laser ranging scheme is proposed for enhanced distance resolution and a common time standard for the entire system. Three frequency combs with different repetition rates are used as light sources at the two ends where the distance is measured. Pulse positions are determined through asynchronous optical sampling and type II second harmonic generation. Results show that the system achieves a maximum residual of 379.6 nm and a standard deviation of 92.9 nm with 2000 averages over 23.6 m. Moreover, as for the frequency transfer, an atom clock and an adjustable signal generator, synchronized to the atom clock, are used as time standards for the two ends to appraise the frequency deviation introduced by the proposed system. The system achieves a residual fractional deviation of 1.3 × 10-16 for 1 s, allowing precise frequency transfer between the two clocks at the two ends.

  12. A single comb laser source for short reach WDM interconnects

    NASA Astrophysics Data System (ADS)

    Wojcik, Gregory L.; Yin, Dongliang; Kovsh, Alexey R.; Gubenko, Alexey E.; Krestnikov, Igor L.; Mikhrin, Sergey S.; Livshits, Daniil A.; Fattal, David A.; Fiorentino, Marco; Beausoleil, Raymond G.

    2009-02-01

    High-channel-count WDM will eventually be used for short reach optical interconnects since it maximizes link bandwidth and efficiency. An impediment to adoption is the fact that each WDM wavelength currently requires its own DFB laser. The alternative is a single, multi-wavelength laser, but noise, size and/or expense make existing options impractical. In contrast, a new low-noise, diode comb laser based on InAs/GaAs quantum dots provides a practical and timely alternative, albeit in the O-band. Samples are being evaluated in short reach WDM development systems. Tests show this type of Fabry-Perot laser permits >10 Gb/s error-free modulation of 10 to over 50 separate channels, as well as potential for 1.25 Gb/s direct modulation. The paper describes comb laser requirements, noise measurements for external and direct modulation, O-band issues, transmitter photonic circuitry and components, future CMP applications, and optical couplers that may help drive down packaging costs to below a dollar.

  13. k-domain linearization of wavelength-swept laser for optical coherence tomography

    NASA Astrophysics Data System (ADS)

    Lee, Byoung Chang; Jeon, Min Yong; Eom, Tae Joong

    2011-03-01

    We propose a new method for k-domain linearization using fiber Bragg gratings (FBGs) in a wavelength-swept source for optical coherence tomography (OCT). A wavelength-swept source with a scanning fiber Fabry-Perot tunable filter is constructed using a conventional ring laser cavity. Five FBGs are used to recalibrate the nonlinear response from the wavelength-swept source. We achieved good quality sample imaging using the k-domain linearization algorithm based on FBGs. The sensitivity at 2 mm is improved by more than 10 dB after k-domain linearization.

  14. Three-dimensional surface phase imaging based on integrated thermo-optic swept laser

    NASA Astrophysics Data System (ADS)

    Kim, Hyo Jin; Cho, Jaedu; Noh, Young-Ouk; Oh, Min-Cheol; Chen, Zhongping; Kim, Chang-Seok

    2014-03-01

    We developed an optical frequency domain imaging (OFDI) system based on an integrated thermo-optic swept laser to achieve three-dimensional surface imaging. The wavelength was swept by applying a heating signal to a thermo-optic polymeric waveguide. The sub-micrometer surface profile was converted from the three-dimensional phase information of the OFDI system on various samples used as resolution targets with a step height of 120 nm.

  15. Frequency comb generation by CW laser injection into a quantum-dot mode-locked laser.

    PubMed

    Pinkert, T J; Salumbides, E J; Tahvili, M S; Ubachs, W; Bente, E A J M; Eikema, K S E

    2012-09-10

    We report on frequency comb generation at 1.5 μm by injection of a CW laser in a hybridly mode-locked InAs/InP two-section quantum-dot laser (HMLQDL). The generated comb has > 60 modes spaced by ∼ 4.5 GHz and a -20 dBc width of > 100 GHz (23 modes) at > 30 dB signal to background ratio. Comb generation was observed with the CW laser (red) detuned more than 20 nm outside the HMLQDL spectrum, spanning a large part of the gain spectrum of the quantum dot material. It is shown that the generated comb is fully coherent with the injected CW laser and RF frequency used to drive the hybrid mode-locking. This method of comb generation is of interest for the creation of small and robust frequency combs for use in optical frequency metrology, high-frequency (> 100 GHz) RF generation and telecommunication applications. PMID:23037259

  16. Development of femtosecond optical frequency comb laser tracker

    NASA Astrophysics Data System (ADS)

    Yang, Ju-qing; Zhou, Wei-hu; Dong, Deng-feng; Zhang, Zi-li; Lao, Da-bao; Ji, Rong-yi; Wang, Da-yong

    2016-01-01

    A new type femtosecond laser tracker is one high precision measurement instrument with urgent need in science research region and industrial manufacture field. This paper focuses on the operational principle and the structure development of the femtosecond laser tracer, and the method of error compensation as well. The system modules were studied and constructed. The femtosecond frequency comb module was firstly analyzed and developed. The femtosecond laser frequency comb performed perfectly high precise distance measurement for laser tracker. The experimental result showed that the stability of repetition rate reached 3.0×10-12@1s and the stability of carrier envelop offset reached 1.0×10-10@1s. The initial experiment showed that measurement error was less than 1ppm. Later the error compensation module was introduced, and the optoelectronic aiming and tracking control module was built. The actual test result showed that the stability of miss distance was better than 2.0 μm, the tracking speed could reach 2m/s.

  17. Precision Spectroscopy of Hydrogen and Femtosecond Laser Frequency Combs

    NASA Astrophysics Data System (ADS)

    Udem, Thomas

    2006-03-01

    A femtosecond frequency comb is a simple and compact tool that allows the phase coherent connection of the radio frequency domain (below 100 GHz) with the optical domain (above 200 THz). It greatly simplified high precision optical frequency measurements and provides the long awaited clockwork mechanism for an all-optical atomic clock. We have used such a frequency comb to measure the absolute frequency of the 1S-2S two-photon transition in atomic hydrogen, i.e. comparing it with the Cs ground state hyperfine splitting. By comparing data taken in 2003 with earlier measurements in 1999 we can set an upper limit on the variation of the 1S-2S transition frequency of (-29 ±57) Hz within 44 months. To derive limits on the drift rates of fundamental constant such as the fine structure constant, we combine these measurements with other optical frequency measurements in Hg^+ and in Yb^+ performed at NIST, Boulder/USA and at PTB, Braunschweig/Germany respectively. This combined method gives precise and separate restrictions for the fractional time variation of the fine structure constant and the Cs nuclear magnetic moment measured in Bohr magnetons. The latter is a measure of the drift rate of the strong interaction. We also report on efforts to convert the frequency comb technology to much shorter wavelength. Based on intra cavity high harmonic generation an XUV (up to 60 nm) frequency comb is generated with a repetition rate of more than 100 MHz useful for high resolution laser spectroscopy in this region.

  18. Comb-referenced laser distance interferometer for industrial nanotechnology.

    PubMed

    Jang, Yoon-Soo; Wang, Guochao; Hyun, Sangwon; Kang, Hyun Jay; Chun, Byung Jae; Kim, Young-Jin; Kim, Seung-Woo

    2016-01-01

    A prototype laser distance interferometer is demonstrated by incorporating the frequency comb of a femtosecond laser for mass-production of optoelectronic devices such as flat panel displays and solar cell devices. This comb-referenced interferometer uses four different wavelengths simultaneously to enable absolute distance measurement with the capability of comprehensive evaluation of the measurement stability and uncertainty. The measurement result reveals that the stability reaches 3.4 nm for a 3.8 m distance at 1.0 s averaging, which further reduces to 0.57 nm at 100 s averaging with a fractional stability of 1.5 × 10(-10). The uncertainty is estimated to be in a 10(-8) level when distance is measured in air due to the inevitable ambiguity in estimating the refractive index, but it can be enhanced to a 10(-10) level in vacuum. PMID:27558016

  19. Comb-referenced laser distance interferometer for industrial nanotechnology

    PubMed Central

    Jang, Yoon-Soo; Wang, Guochao; Hyun, Sangwon; Kang, Hyun Jay; Chun, Byung Jae; Kim, Young-Jin; Kim, Seung-Woo

    2016-01-01

    A prototype laser distance interferometer is demonstrated by incorporating the frequency comb of a femtosecond laser for mass-production of optoelectronic devices such as flat panel displays and solar cell devices. This comb-referenced interferometer uses four different wavelengths simultaneously to enable absolute distance measurement with the capability of comprehensive evaluation of the measurement stability and uncertainty. The measurement result reveals that the stability reaches 3.4 nm for a 3.8 m distance at 1.0 s averaging, which further reduces to 0.57 nm at 100 s averaging with a fractional stability of 1.5 × 10−10. The uncertainty is estimated to be in a 10−8 level when distance is measured in air due to the inevitable ambiguity in estimating the refractive index, but it can be enhanced to a 10−10 level in vacuum. PMID:27558016

  20. Direct frequency comb two-photon laser cooling and trapping

    NASA Astrophysics Data System (ADS)

    Long, Xueping; Jayich, Andrew; Campbell, Wesley C.

    2016-05-01

    Generating and manipulating high energy photons for spectroscopy on electric dipole transitions of atoms and molecules with deeply bound valence electrons is difficult. Further, laser cooling of such species is even more challenging for lack of laser power. A possible solution is to drive two-photon transitions. This may alleviate the photon energy problem and open the door to cold, trapped samples of highly desirable species with tightly bound electrons. We perform a proof of principle experiment with rubidium by driving a two-photon transition with an optical frequency comb. We perform optical cooling and extend this technique to trapping, where we are able to make a magneto-optical trap in one dimension. This work is supported by the National Science Foundation CAREER program.

  1. High performance tunnel injection quantum dot comb laser

    SciTech Connect

    Lee, C.-S.; Guo Wei; Basu, Debashish; Bhattacharya, Pallab

    2010-03-08

    A high-speed multiwavelength quantum dot comb laser, grown by molecular beam epitaxy, is demonstrated. The device is characterized with a 75.9 nm (full width at half maximum) and a 91.4 nm (DELTA{sub -15dB}) wide lasing spectrum. There are 105 and 185 simultaneously emitted longitudinal modes with a maximum channel intensity nonuniformity of less than 3 dB in the spectral range of 1231-1252 nm and 1274-1311 nm, respectively, for a laser with 1040 mum cavity length. The channel spacing can be tuned with cavity length and remains invariant in the temperature range of 300-323 K. The small signal modulation bandwidth is 7.5 GHz.

  2. Calibration of an echelle spectrograph with an astro-comb: a laser frequency comb with very high repetition rate

    NASA Astrophysics Data System (ADS)

    Phillips, David F.; Glenday, Alex; Li, Chih-Hao; Furesz, Gabor; Benedick, Andrew J.; Chang, Guoqing N.; Chen, Li-Jin; Korzennik, Sylvain; Sasselov, Dimitar; Kaertner, Franz X.; Szentgyorgyi, Andrew; Walsworth, Ronald L.

    2012-09-01

    Searches for extrasolar planets using precision radial velocity (PRV) techniques are approaching Earth-like planet sensitivity, however require an improvement of one order of magnitude to identify earth-mass planets in the habitable zone of sun-like stars. A key limitation is spectrograph calibration. An astro-comb, an octave-spanning laser frequency comb and a Fabry-Pérot cavity, producing evenly spaced frequencies with large wavelength coverage, is a promising tool for improved wavelength calibration. We demonstrate the calibration of a high-resolution astrophysical spectrograph below the 1 m/s level in the 8000-9000 Å and 4200 Å spectral bands.

  3. Wide Tuning Range Wavelength-Swept Laser With Two Semiconductor Optical Amplifiers

    PubMed Central

    Oh, W. Y.; Yun, S. H.; Tearney, G. J.; Bouma, B. E.

    2010-01-01

    We demonstrate a wide tuning range high-speed wavelength-swept semiconductor laser based on a polygon scanning filter that is common to two laser cavities. Linear wavelength tuning was achieved over 145 nm around 1310 nm at a tuning repetition rate of 20 kHz. The wavelength tuning filter is expandable to accommodate multiple semiconductor optical amplifiers for further widening of the laser wavelength tuning range. PMID:20651947

  4. Wavelength-swept Tm-doped fiber laser operating in the two-micron wavelength band.

    PubMed

    Tokurakawa, M; Daniel, J M O; Chenug, C S; Liang, H; Clarkson, W A

    2014-08-25

    A wavelength-swept thulium-doped silica fiber laser using an intracavity rotating slotted-disk wavelength scanning filter in combination with an intracavity solid etalon for passive control of temporal and spectral profiles is reported. The laser yielded a wavelength swept output in a step-wise fashion with each laser pulse separated from the previous pulse by a frequency interval equal to the free-spectral-range of the etalon and with an instantaneous linewidth of <0.05 nm. Scanning ranges from 1905 nm to 2049 nm for a cladding-pumping laser configuration, and from 1768 nm to 1956 nm for a core-pumping laser configuration were achieved at average output powers up to ~1 W. PMID:25321211

  5. High-performance, vibration-immune, fiber-laser frequency comb.

    PubMed

    Baumann, Esther; Giorgetta, Fabrizio R; Nicholson, Jeffrey W; Swann, William C; Coddington, Ian; Newbury, Nathan R

    2009-03-01

    We demonstrate an environmentally robust optical frequency comb based on a polarization-maintaining, all-fiber, figure-eight laser. The comb is phase locked to a cavity-stabilized cw laser by use of an intracavity electro-optic phase modulator yielding 1.6 MHz feedback bandwidth. This high bandwidth provides close to shot-noise-limited residual phase noise between the comb and cw reference laser of -94 dBc/Hz from 20 Hz to 200 kHz and an integrated in-loop phase noise of 32 mrad from 1 Hz to 1 MHz. Moreover, the comb remains phase locked under significant mechanical vibrations of over 1 g. This level of environmental robustness is an important step toward a fieldable fiber frequency comb. PMID:19252577

  6. Calibration of an astrophysical spectrograph below 1 m/s using a laser frequency comb

    NASA Astrophysics Data System (ADS)

    Phillips, David F.; Glenday, Alexander G.; Li, Chih-Hao; Cramer, Claire; Furesz, Gabor; Chang, Guoqing; Benedick, Andrew J.; Chen, Li-Jin; Kärtner, Franz X.; Korzennik, Sylvain; Sasselov, Dimitar; Szentgyorgyi, Andrew; Walsworth, Ronald L.

    2012-06-01

    We deployed two wavelength calibrators based on laser frequency combs ("astro-combs") at an astronomical telescope. One astro-comb operated over a 100 nm band in the deep red (∼ 800 nm) and a second operated over a 20 nm band in the blue (∼ 400 nm). We used these red and blue astro-combs to calibrate a high-resolution astrophysical spectrograph integrated with a 1.5 m telescope, and demonstrated calibration precision and stability suffici ent to enable detection of changes in stellar radial velocity < 1 m/s.

  7. Calibration of an astrophysical spectrograph below 1 m/s using a laser frequency comb.

    PubMed

    Phillips, David F; Glenday, Alexander G; Li, Chih-Hao; Cramer, Claire; Furesz, Gabor; Chang, Guoqing; Benedick, Andrew J; Chen, Li-Jin; Kärtner, Franz X; Korzennik, Sylvain; Sasselov, Dimitar; Szentgyorgyi, Andrew; Walsworth, Ronald L

    2012-06-18

    We deployed two wavelength calibrators based on laser frequency combs ("astro-combs") at an astronomical telescope. One astro-comb operated over a 100 nm band in the deep red (∼ 800 nm) and a second operated over a 20 nm band in the blue (∼ 400 nm). We used these red and blue astro-combs to calibrate a high-resolution astrophysical spectrograph integrated with a 1.5 m telescope, and demonstrated calibration precision and stability sufficient to enable detection of changes in stellar radial velocity < 1 m/s. PMID:22714437

  8. Skin friction measurements by laser interferometry in swept shock wave/turbulent boundary-layer interactions

    NASA Technical Reports Server (NTRS)

    Kim, Kwang-Soo; Settles, Gary S.

    1988-01-01

    The laser interferometric skin friction meter was used to measure wall shear stress distributions in two interactions of fin-generated swept shock waves with turbulent boundary layers. The basic research configuration was an unswept sharp-leading-edge fin of variable angle mounted on a flatplate. The results indicate that such measurements are practical in high-speed interacting flows, and that a repeatability of + or - 6 percent or better is possible. Marked increases in wall shear were observed in both swept interactions tested.

  9. Solar oscillations and the search for Venus enabled by a laser frequency comb

    NASA Astrophysics Data System (ADS)

    Phillips, David F.; Glenday, Alexander G.; Li, Chih-Hao; Langellier, Nicholas; Chang, Guoqing; Furesz, Gabor; Kaertner, Franz X.; Sasselov, Dimitar; Szentgyorgyi, Andrew; Walsworth, Ronald L.

    2015-05-01

    We have recently demonstrated sub-m/s sensitivity in measuring the radial velocity (RV) between the Earth and Sun using a simple, home-built solar telescope feeding the HARPS-N spectrograph at the Italian National Telescope calibrated with our green astro-comb. The green astro-comb is a laser frequency comb optimized for calibrating astrophysical spectrographs. We plan, in the coming year, to use the astro-comb calibrated spectrograph and solar telescope to detect the solar RV signal induced by Venus and thus demonstrate sensitivity of these instruments to detect terrestrial exoplanets. Here, we will present the astro-comb, results from the astro-comb calibrating the HARPS-N exoplanet searcher spectrograph, solar RV stability and plans for observing the signature of Venus.

  10. Phase-locked, erbium-fiber-laser-based frequency comb in the near infrared.

    PubMed

    Washburn, Brian R; Diddams, Scott A; Newbury, Nathan R; Nicholson, Jeffrey W; Yan, Man F; Jørgensen, Carsten G

    2004-02-01

    A phase-locked frequency comb in the near infrared is demonstrated with a mode-locked, erbium-doped, fiber laser whose output is amplified and spectrally broadened in dispersion-flattened, highly nonlinear optical fiber to span from 1100 to >2200 nm. The supercontinuum output comprises a frequency comb with a spacing set by the laser repetition rate and an offset by the carrier-envelope offset frequency, which is detected with the standard f-to-2f heterodyne technique. The comb spacing and offset frequency are phase locked to a stable rf signal with a fiber stretcher in the laser cavity and by control of the pump laser power, respectively. This infrared comb permits frequency metrology experiments in the near infrared in a compact, fiber-laser-based system. PMID:14759041

  11. 115 kHz tuning repetition rate ultrahigh-speed wavelength-swept semiconductor laser

    PubMed Central

    Oh, W. Y.; Yun, S. H.; Tearney, G. J.; Bouma, B. E.

    2009-01-01

    We demonstrate an ultrahigh-speed wavelength-swept semiconductor laser using a polygon-based wavelength scanning filter. With a polygon rotational speed of 900 revolutions per second, a continuous wavelength tuning rate of 9200 nm/ms and a tuning repetition rate of 115 kHz were achieved. The wavelength tuning range of the laser was 80 nm centered at 1325 nm, and the average polarized output power was 23 mW. PMID:16350273

  12. Breathing laser as an inertia-free swept source for high-quality ultrafast optical bioimaging.

    PubMed

    Wei, Xiaoming; Xu, Jingjiang; Xu, Yiqing; Yu, Luoqin; Xu, Jianbing; Li, Bowen; Lau, Andy K S; Wang, Xie; Zhang, Chi; Tsia, Kevin K; Wong, Kenneth K Y

    2014-12-01

    We demonstrate an all-fiber breathing laser as inertia-free swept source (BLISS), with an ultra-compact design, for the emerging ultrafast bioimaging modalities. The unique feature of BLISS is its broadband wavelength-swept operation (∼60  nm) with superior temporal stability in terms of both long term (0.08 dB over 27 h) and shot-to-shot power variations (2.1%). More importantly, it enables a wavelength sweep rate of >10  MHz (∼7×10⁸  nm/s)—orders-of-magnitude faster than the existing swept sources based on mechanical or electrical tuning techniques. BLISS thus represents a practical and new generation of swept source operating in the unmet megahertz swept-rate regime that aligns with the pressing need for scaling the optical bioimaging speed in ultrafast phenomena study or high-throughput screening applications. To showcase its utility in high-speed optical bioimaging, we here employ BLISS for ultrafast time-stretch microscopy and multi-MHz optical coherence tomography of the biological specimen at a single-shot line-scan rate or A-scan rate of 11.5 MHz. PMID:25490629

  13. Noise dynamics of a prism-based Cr:forsterite laser frequency comb

    NASA Astrophysics Data System (ADS)

    Wu, Shun; Washburn, Brian; Corwin, Kristan; Tillman, Karl

    2010-03-01

    Mode-locked Cr:forsterite lasers are of significant interest as infrared frequency combs due to their ability to generate stable high repetition rate femtosecond pulses. However, self-referenced Cr:forsterite frequency combs tend to exhibit wide carrier-envelope offset frequency (f0) linewidths. These large f0 linewidths can be attributed to significant frequency noise across the comb's spectral bandwidth and result in broad comb teeth. We have stabilized a prism-based Cr:forsterite frequency comb and observed narrowing of the f0 linewidth from ˜1 MHz down to <100 kHz when a knife edge is inserted into the intracavity beam as a spectral filter. This can also be further reduced after phase-locking the comb to a low-phase noise rf oscillator. Thus, the introduction of an intracavity knife edge significantly reduces the frequency noise of the system and enables more effective stabilization of the entire comb. A theoretical model has been used to investigate the noise dynamics of the phase-stabilized comb system. It includes: the pump laser power (P), the frequency dependence of the f0 response to pump power changes ((df0/dP)(ν)), and the frequency dependence of the femtosecond laser's relative intensity noise, RIN(ν). Supported by AFOSR FA9950-05-1-0304 and NSF ECS-0449295

  14. Stabilized frequency comb with a self-referenced femtosecond Cr:forsterite laser.

    PubMed

    Kim, K; Washburn, B R; Wilpers, G; Oates, C W; Hollberg, L; Newbury, N R; Diddams, S A; Nicholson, J W; Yan, M F

    2005-04-15

    A frequency comb is generated with a Cr:forsterite femtosecond laser, spectrally broadened through a highly nonlinear optical fiber to span from 1.0 to 2.2 ,m, and stabilized using the f-to-2f self-referencing technique. The repetition rate and the carrier-envelope offset frequency are stabilized to a hydrogen maser, calibrated by a cesium atomic fountain clock. Simultaneous frequency measurement of a 657-nm cw laser by use of the stabilized frequency combs from this Cr:forsterite system and a Ti:sapphire laser agree at the 10(-13) level. The frequency noise of the comb components is observed at 1064, 1314, and 1550 nm by comparing the measured beat frequencies between cw lasers and the supercontinuum frequency combs. PMID:15865403

  15. Wide and fast wavelength-swept fiber lasers based on dispersion tuning and their application to optical coherence tomography

    NASA Astrophysics Data System (ADS)

    Yamashita, Shinji; Takubo, Yuya

    2013-12-01

    We recently proposed a new class of wavelength-swept lasers for swept-source optical coherence tomography (SS-OCT). It uses the same gain medium with the conventional swept lasers, but does not require any tunable filters. It is based on a principle called "dispersion tuning", in which a highly dispersive medium is inserted in the laser cavity, and loss/gain modulation is applied to mode-lock the laser. Since the cavity contains no mechanical components, such as tunable filters, we could achieve the very high sweep rate. In this review paper, we describe the principle of the dispersion-tuned swept lasers in detail and present our recent work on the application to the SS-OCT system.

  16. An Optical Frequency Comb Tied to GPS for Laser Frequency/Wavelength Calibration.

    PubMed

    Stone, Jack A; Egan, Patrick

    2010-01-01

    Optical frequency combs can be employed over a broad spectral range to calibrate laser frequency or vacuum wavelength. This article describes procedures and techniques utilized in the Precision Engineering Division of NIST (National Institute of Standards and Technology) for comb-based calibration of laser wavelength, including a discussion of ancillary measurements such as determining the mode order. The underlying purpose of these calibrations is to provide traceable standards in support of length measurement. The relative uncertainty needed to fulfill this goal is typically 10(-8) and never below 10(-12), very modest requirements compared to the capabilities of comb-based frequency metrology. In this accuracy range the Global Positioning System (GPS) serves as an excellent frequency reference that can provide the traceable underpinning of the measurement. This article describes techniques that can be used to completely characterize measurement errors in a GPS-based comb system and thus achieve full confidence in measurement results. PMID:27134794

  17. An Optical Frequency Comb Tied to GPS for Laser Frequency/Wavelength Calibration

    PubMed Central

    Stone, Jack A.; Egan, Patrick

    2010-01-01

    Optical frequency combs can be employed over a broad spectral range to calibrate laser frequency or vacuum wavelength. This article describes procedures and techniques utilized in the Precision Engineering Division of NIST (National Institute of Standards and Technology) for comb-based calibration of laser wavelength, including a discussion of ancillary measurements such as determining the mode order. The underlying purpose of these calibrations is to provide traceable standards in support of length measurement. The relative uncertainty needed to fulfill this goal is typically 10−8 and never below 10−12, very modest requirements compared to the capabilities of comb-based frequency metrology. In this accuracy range the Global Positioning System (GPS) serves as an excellent frequency reference that can provide the traceable underpinning of the measurement. This article describes techniques that can be used to completely characterize measurement errors in a GPS-based comb system and thus achieve full confidence in measurement results. PMID:27134794

  18. Picosecond pulses from wavelength-swept continuous-wave Fourier domain mode-locked lasers

    NASA Astrophysics Data System (ADS)

    Eigenwillig, Christoph M.; Wieser, Wolfgang; Todor, Sebastian; Biedermann, Benjamin R.; Klein, Thomas; Jirauschek, Christian; Huber, Robert

    2013-05-01

    Ultrafast lasers have a crucial function in many fields of science; however, up to now, high-energy pulses directly from compact, efficient and low-power semiconductor lasers are not available. Therefore, we introduce a new approach based on temporal compression of the continuous-wave, wavelength-swept output of Fourier domain mode-locked lasers, where a narrowband optical filter is tuned synchronously to the round-trip time of light in a kilometre-long laser cavity. So far, these rapidly swept lasers enabled orders-of-magnitude speed increase in optical coherence tomography. Here we report on the generation of ~60-70 ps pulses at 390 kHz repetition rate. As energy is stored optically in the long-fibre delay line and not as population inversion in the laser-gain medium, high-energy pulses can now be generated directly from a low-power, compact semiconductor-based oscillator. Our theory predicts subpicosecond pulses with this new technique in the future.

  19. Simultaneous 1310/1550 dual-band swept laser source and fiber-based dual-band common-path swept source optical coherence tomography

    NASA Astrophysics Data System (ADS)

    Mao, Youxin; Chang, Shoude; Murdock, Erroll; Flueraru, Costel

    2011-08-01

    A simultaneous two wavelength band swept laser source and a fiber-based dual-band common-path swept source optical coherence tomography is reported. Simultaneous 1310/1550 dual-wavelength tuning is performed by using two fiber-ring cavities with corresponding optical semiconductor amplifier as their gain mediums and two narrowband optical filters with a single dual-window polygonal scanner. Measured average output powers of 60 mW and 27 mW have been achieved for 1310 and 1550 nm bands, respectively, while the two wavelengths were swept simultaneously from 1227 nm to 1387 nm for 1310 nm band and from 1519 nm to 1581 nm for 1550 nm band at an A-scan rate of 65 kHz. A broadband 1310/1550 wavelength-division multiplexing is used for coupling two wavelengths into a common-path single-mode GRIN-lensed fiber probe to form a dual-band common-path swept-source optical coherence tomography. Simultaneous OCT imaging at 1310 and 1550 nm is achieved by using a depth ratio correction method. This technique allows potentially for in vivo endoscopic high-speed functional OCT imaging with high quality spectroscopic contrast with low computational costs. On the other hand, the common path configuration is able to reject common mode noise and potentially implement high stability quantitative phase measurements.

  20. Selection and amplification of modes of an optical frequency comb using a femtosecond laser injection-locking technique

    SciTech Connect

    Moon, H. S.; Kim, E. B.; Park, S. E.; Park, C. Y.

    2006-10-30

    The authors have demonstrated the selection and the amplification of the components of an optical frequency comb using a femtosecond laser injectionlocking technique. The author used a mode-locked femtosecond Ti:sapphire laser as the master laser and a single-mode diode laser as the slave laser. The femtosecond laser injection-locking technique was applied to a filter for mode selection of the optical frequency comb and an amplifier for amplification of the selected mode. The authors could obtain the laser source selected only the desired mode of the optical frequency comb and amplified the power of the selected modes several thousand times.

  1. Numerical investigation into the injection-locking phenomena of gain switched lasers for optical frequency comb generation

    SciTech Connect

    Ó Dúill, Sean P. Anandarajah, Prince M.; Zhou, Rui; Barry, Liam P.

    2015-05-25

    We present detailed numerical simulations of the laser dynamics that describe optical frequency comb formation by injection-locking a gain-switched laser. The typical rate equations for semiconductor lasers including stochastic carrier recombination and spontaneous emission suffice to show the injection-locking behavior of gain switched lasers, and we show how the optical frequency comb evolves starting from the free-running state, right through the final injection-locked state. Unlike the locking of continuous wave lasers, we show that the locking range for gain switched lasers is considerably greater because injection locking can be achieved by injecting at frequencies close to one of the comb lines. The quality of the comb lines is formally assessed by calculating the frequency modulation (FM)-noise spectral density and we show that under injection-locking conditions the FM-noise spectral density of the comb lines tend to that of the maser laser.

  2. Frequency-comb-assisted broadband precision spectroscopy with cascaded diode lasers.

    PubMed

    Liu, Junqiu; Brasch, Victor; Pfeiffer, Martin H P; Kordts, Arne; Kamel, Ayman N; Guo, Hairun; Geiselmann, Michael; Kippenberg, Tobias J

    2016-07-01

    Frequency-comb-assisted diode laser spectroscopy, employing both the accuracy of an optical frequency comb and the broad wavelength tuning range of a tunable diode laser, has been widely used in many applications. In this Letter, we present a novel method using cascaded frequency agile diode lasers, which allows us to extend the measurement bandwidth to 37.4 THz (1355-1630 nm) at megahertz resolution with scanning speeds above 1 THz/s. It is demonstrated as a useful tool to characterize a broadband spectrum for molecular spectroscopy, and in particular it enables us to characterize the dispersion of integrated microresonators up to the 4th-order. PMID:27367120

  3. Traceability of laser frequency/wavelength calibration through the frequency comb at Inmetro

    NASA Astrophysics Data System (ADS)

    Silva, I. L. M.; Couceiro, I. B.; Torres, M. A. C.; Costa, P. A.; Grieneisen, H. P. H.

    2016-07-01

    The acquisition of a femtosecond laser comb by the Optical Metrology Division of Inmetro now allows for carrying out high precision calibrations of optical frequencies for lasers which are used as standards of the length unit with gauge block interferometers. The frequency comb is operated as an optical frequency synthesizer and is presently linked to the time unit by a 10 MHz oscillator which is disciplined by GPS. Laser frequencies are determined with accuracy in the range of few parts in 1012. This measurement method now links the length unit, meter, to the SI-second attending the recommendation by the BIPM.

  4. Mid-infrared frequency comb based on a quantum cascade laser.

    PubMed

    Hugi, Andreas; Villares, Gustavo; Blaser, Stéphane; Liu, H C; Faist, Jérôme

    2012-12-13

    Optical frequency combs act as rulers in the frequency domain and have opened new avenues in many fields such as fundamental time metrology, spectroscopy and frequency synthesis. In particular, spectroscopy by means of optical frequency combs has surpassed the precision and speed of Fourier spectrometers. Such a spectroscopy technique is especially relevant for the mid-infrared range, where the fundamental rotational-vibrational bands of most light molecules are found. Most mid-infrared comb sources are based on down-conversion of near-infrared, mode-locked, ultrafast lasers using nonlinear crystals. Their use in frequency comb spectroscopy applications has resulted in an unequalled combination of spectral coverage, resolution and sensitivity. Another means of comb generation is pumping an ultrahigh-quality factor microresonator with a continuous-wave laser. However, these combs depend on a chain of optical components, which limits their use. Therefore, to widen the spectroscopic applications of such mid-infrared combs, a more direct and compact generation scheme, using electrical injection, is preferable. Here we present a compact, broadband, semiconductor frequency comb generator that operates in the mid-infrared. We demonstrate that the modes of a continuous-wave, free-running, broadband quantum cascade laser are phase-locked. Combining mode proliferation based on four-wave mixing with gain provided by the quantum cascade laser leads to a phase relation similar to that of a frequency-modulated laser. The comb centre carrier wavelength is 7 micrometres. We identify a narrow drive current range with intermode beat linewidths narrower than 10 hertz. We find comb bandwidths of 4.4 per cent with an intermode stability of less than or equal to 200 hertz. The intermode beat can be varied over a frequency range of 65 kilohertz by radio-frequency injection. The large gain bandwidth and independent control over the carrier frequency offset and the mode spacing

  5. Ultra broadband microwave frequency combs generated by an optical pulse-injected semiconductor laser.

    PubMed

    Juan, Yu-Shan; Lin, Fan-Yi

    2009-10-12

    We have demonstrated and characterized the generation of ultra broadband microwave frequency combs with an optical pulse-injected semiconductor laser. Through optical pulse injection, the microwave frequency combs generated in the slave laser (SL) have bandwidths greater than 20 GHz within a +/-5 dB amplitude variation, which is almost 3-fold of the 7 GHz relaxation oscillation frequency of the laser used. The line spacing of the comb is tunable from 990 MHz to 2.6 GHz, determined by the repetition frequency of the injection optical pulses produced by the master laser (ML) with optoelectronic feedback. At an offset frequency of 200 kHz, a single sideband (SSB) phase noise of -60 dBc/kHz (-90 dBc/Hz estimated) in the 1(st) harmonic is measured while a noise suppression relative to the injected regular pulsing state of the ML of more than 25 dB in the 17(th) harmonic is achieved. A pulsewidth of 29 ps and a ms timing jitter of 18.7 ps are obtained in the time domain for the microwave frequency comb generated. Further stabilization is realized by modulating the ML at the fundamental frequency of the injected regular pulsing state. The feasibility of utilizing the generated microwave frequency comb in frequency conversion and signal broadcasting is also explored. The conversion gain of each channel increases linearly as the signal power increases with a ratio of about 0.81 dB/dBm. PMID:20372590

  6. Monolithically integrated low linewidth comb source using gain switched slotted Fabry-Perot lasers.

    PubMed

    Alexander, J K; Morrissey, P E; Yang, H; Yang, M; Marraccini, P J; Corbett, B; Peters, F H

    2016-04-18

    A monolithically integrated low linewidth optical comb is demonstrated by gain switching of a three-section laser device. The device consists of a slave and master section separated by a shared slotted mirror section. Wavelength tunability has been demonstrated by varying the electrical bias of each section. The number of comb lines is shown to almost double with the addition of optical injection from the master section into the slave. The unmodulated device has a full width half max linewidth of ∼ 500 kHz, while the comb line set were measured to be ∼ 600 kHz, with little degradation as a result of gain switching. The FSR (free spectral range) of the demonstrated comb is 4 GHz, which is tunable within the bandwidth of the device, with a central wavelength of 1580.3 nm. PMID:27137237

  7. A Precision Radial Velocity Pathfinder Instrument in the H Band with a Laser Frequency Comb

    NASA Astrophysics Data System (ADS)

    Terrien, Ryan; Mahadevan, S.; Ramsey, L.; Bender, C.; Redman, S.; Osterman, S.; Diddams, S.; Ycas, G.; Quinlan, F.; Botzer, B.

    2011-01-01

    We describe changes to the warm-bench, fiber-fed, Penn State Pathfinder instrument that enabled us to test the ability to recover precision radial velocities in the H-band. The use of thermal blocking filters that cut off at 1.7 microns allows us to observe in the H-band by blocking the overwhelming thermal flux beyond 2 microns. A PK-50 window provides further suppression of this thermal flux. We also describe the observations, reduction, and results from an August 2010 test run of this instrument with a 25 GHz NIST laser frequency comb calibration system. We obtained radial velocities of several bright stars with on-sky observation with the laser comb. Our results demonstrate the potential of our testbed configuration for obtaining precision radial velocities in the NIR, as well as the utility of laser frequency combs as wavelength calibrators in this wavelength regime.

  8. Combined tunable filters based swept laser source for optical coherence tomography

    NASA Astrophysics Data System (ADS)

    Chen, Minghui; Ding, Zhihua; Wang, Cheng; Huang, Yimei; Chen, Rong; Song, Chengli

    2013-03-01

    We demonstrate a novel ultra-broad tunable bandwidth and narrow instantaneous line-width swept laser source using combined tunable filters working at 1290 nm center wavelength for application in optical coherence tomography. The combined filters consist of a fiber Fabry-Perot tunable filter (FFP-TF) and a polygon mirror with scanning grating based filter. The FFP-TF has the narrow free spectral range (FSR) but ultra-high spectral resolution (narrow instantaneous bandwidth) driven at high frequency far from resonant frequency. The polygon filter in the Littrow configuration is composed of fiber collimator, polygon mirror driven by function generator, and diffractive grating with low groove. Polygon filter coarsely tunes with wide turning range and then FFP-TF finely tunes with narrow band-pass filtering. In contrast to traditional method using single tunable filter, the trade-off between bandwidth and instantaneous line-width is alleviated. The combined filters can realize ultra wide scan range and fairly narrow instantaneous bandwidth simultaneously. Two semiconductor optical amplifiers (SOA) in the parallel manner are used as the gain medium. The wide bandwidth could be obtained by these parallel SOAs to be suitable for sufficient wide range of the polygon filter's FSR because each SOA generates its own spectrum independently. The proposed swept laser source provides an edge-to-edge scanning range of 180 nm covering 1220 to 1400 nm with instantaneous line-width of about 0.03 nm at sweeping rate of 23.3 kHz. The swept laser source with combined filters offers broadband tunable range with narrow instantaneous line-width, which especially benefits for high resolution and deep imaging depth optical frequency domain imaging.

  9. Multiheterodyne spectroscopy with optical frequency combs generated from a continuous-wave laser.

    PubMed

    Long, D A; Fleisher, A J; Douglass, K O; Maxwell, S E; Bielska, K; Hodges, J T; Plusquellic, D F

    2014-05-01

    Dual-drive Mach-Zehnder modulators were utilized to produce power-leveled optical frequency combs (OFCs) from a continuous-wave laser. The resulting OFCs contained up to 50 unique frequency components and spanned more than 200 GHz. Simple changes to the modulation frequency allowed for agile control of the comb spacing. These OFCs were then utilized for broadband, multiheterodyne measurements of CO2 using both a multipass cell and an optical cavity. This technique allows for robust measurements of trace gas species and alleviates much of the cost and complexity associated with the use of femtosecond OFCs produced with mode-locked pulsed lasers. PMID:24784078

  10. Adaptive sampling dual terahertz comb spectroscopy using dual free-running femtosecond lasers

    PubMed Central

    Yasui, Takeshi; Ichikawa, Ryuji; Hsieh, Yi-Da; Hayashi, Kenta; Cahyadi, Harsono; Hindle, Francis; Sakaguchi, Yoshiyuki; Iwata, Tetsuo; Mizutani, Yasuhiro; Yamamoto, Hirotsugu; Minoshima, Kaoru; Inaba, Hajime

    2015-01-01

    Terahertz (THz) dual comb spectroscopy (DCS) is a promising method for high-accuracy, high-resolution, broadband THz spectroscopy because the mode-resolved THz comb spectrum includes both broadband THz radiation and narrow-line CW-THz radiation characteristics. In addition, all frequency modes of a THz comb can be phase-locked to a microwave frequency standard, providing excellent traceability. However, the need for stabilization of dual femtosecond lasers has often hindered its wide use. To overcome this limitation, here we have demonstrated adaptive-sampling THz-DCS, allowing the use of free-running femtosecond lasers. To correct the fluctuation of the time and frequency scales caused by the laser timing jitter, an adaptive sampling clock is generated by dual THz-comb-referenced spectrum analysers and is used for a timing clock signal in a data acquisition board. The results not only indicated the successful implementation of THz-DCS with free-running lasers but also showed that this configuration outperforms standard THz-DCS with stabilized lasers due to the slight jitter remained in the stabilized lasers. PMID:26035687

  11. Spectrally encoded slit confocal microscopy using a wavelength-swept laser

    NASA Astrophysics Data System (ADS)

    Kim, Soocheol; Hwang, Jaehyun; Heo, Jung; Ryu, Suho; Lee, Donghak; Kim, Sang-Hoon; Oh, Seung Jae; Joo, Chulmin

    2015-03-01

    We present an implementation of spectrally encoded slit confocal microscopy. The method employs a rapid wavelength-swept laser as the light source and illuminates a specimen with a line focus that scans through the specimen as the wavelength sweeps. The reflected light from the specimen is imaged with a stationary line scan camera, in which the finite pixel height serves as a slit aperture. This scanner-free operation enables a simple and cost-effective implementation in a small form factor, while allowing for the three-dimensional imaging of biological samples.

  12. A fiber-optic epoxy cure monitoring technique by using a wavelength-swept laser

    NASA Astrophysics Data System (ADS)

    Kim, Hyunjin; Kim, Dae-gil; Sampath, Umesh; Song, Minho

    2015-07-01

    An epoxy cure monitoring system has been constructed by combining fiber grating sensors and Fresnel reflection monitoring. The sensors measure strain and refractive index variations during the curing process, indicating the onset of gelification, the progress, and the end of curing. We used a wavelength-swept laser source to address both types of sensors. The signals from different sensors could be easily separated, resulting in simple optical setup and increased efficiency. The fiber grating sensors are demodulated by a spectrometer. The output fluctuation in the Fresnel reflection was compensated by referencing it with the tapped output of light source.

  13. Programmable high speed (~1MHz) Vernier-mode-locked frequency-swept laser for OCT imaging

    NASA Astrophysics Data System (ADS)

    Kourogi, M.; Kawamura, Y.; Yasuno, Y.; Oyaizu, H.; Miyao, H.; Imai, K.

    2008-02-01

    We propose and demonstrate a programmable high-speed, frequency-swept laser for swept-source optical coherence tomography (SS-OCT). This new technique is based on Vernier effect of two pieces of Fabry-Perot electro-optic modulators. This technique offers a non-mechanical optical filter with high resolution and wide tuning range. By applying it to a Fourier domain mode-locked laser, such sweeps are generated. The Vernier effect filter can be modulated by arbitrary wave forms, thus this laser source can eliminate the rescaling process which is the main bottle-neck of the operation time in SS-OCT by applying frequency sweep to equidistant spacing in frequency. Effective repetition frequencies of 100kHz~1MHz are demonstrated with a tuning range of 17THz (140nm) at 1550nm center wavelength. OCT imaging of in vivo human sweat duct with A-line rate of 100kHz and 300kHz are also demonstrated. The resolution of 12μm~ is realized without rescaling process. We present an analysis which suggests design approaches for optimization performance.

  14. Frequency Swept Diode-pumped Single Frequency TM,Ho:YLiF Laser for spaceborne Doppler Lidar

    NASA Technical Reports Server (NTRS)

    McGuckin, B. T.; Menzies, R. T.; Esproles, C.

    1993-01-01

    Optical heterodyne experiments involving the photomixing of two single frequency, deode-pumped thulium holmium yttrium lithium flouride lasers are described. Operated in external frquency stabilization loops, the lasers exhibit 1MHz short term stability, and are photomixed and offset-locked at 140 MHz. Summation of sine wave modulation onto the PZT control voltage on one laser results in frequency swept operation over a continuous tuning range of 160 MHz.

  15. Study on high coupling efficiency Er-doped fiber laser for femtosecond optical frequency comb

    NASA Astrophysics Data System (ADS)

    Pang, Lihui; Liu, Wenjun; Han, Hainian; Wei, Zhiyi

    2016-09-01

    The femtosecond laser is crucial to the operation of the femtosecond optical frequency comb. In this paper, a passively mode-locked erbium-doped fiber laser is presented with 91.4 fs pulse width and 100.8 MHz repetition rate, making use of the nonlinear polarized evolution effect. Using a 976 nm pump laser diode, the average output power is 16 mW from the coupler and 27 mW from the polarization beam splitter at the pump power of 700 mW. The proposed fiber laser can offer excellent temporal purity in generated pulses with high power, and provide a robust source for fiber-based frequency combs and supercontinuum generation well suited for industrial applications.

  16. Wide and fast wavelength-swept fiber lasers based on dispersion tuning for real-time OCT

    NASA Astrophysics Data System (ADS)

    Yamashita, S.; Takubo, Y.

    2014-05-01

    Swept-Source Optical coherence tomography (SS-OCT) is a powerful tool for fast medical imaging. For the real-time 3D imaging, the wide tuning range over 100 nm and fast sweep rate over 100 kHz are typically required. We recently proposed a new wavelength-swept laser for SS-OCT. It is based on a principle called dispersion tuning. Since the cavity contains no mechanical components, such as tunable filters, we could achieve the very high sweep rate. In this review paper, we describe the principle of the dispersion-tuned swept lasers in detail and present our recent works on the application to the SS-OCT system.

  17. Coherent frequency combs produced by self frequency modulation in quantum cascade lasers

    SciTech Connect

    Khurgin, J. B.; Dikmelik, Y.; Hugi, A.; Faist, J.

    2014-02-24

    One salient characteristic of Quantum Cascade Laser (QCL) is its very short τ ∼ 1 ps gain recovery time that so far thwarted the attempts to achieve self-mode locking of the device into a train of single pulses. We show theoretically that four wave mixing, combined with the short gain recovery time causes QCL to operate in the self-frequency-modulated regime characterized by a constant power in time domain and stable coherent comb in the frequency domain. Coherent frequency comb may enable many potential applications of QCL's in sensing and measurement.

  18. Application of Laser Frequency Combs and Nitrogen Vacancy Diamond Magnetometers to Searches for New Physics

    NASA Astrophysics Data System (ADS)

    Phillips, D. F.; Walsworth, R. L.

    2014-01-01

    Searches for new physics often benefit from improved technologies. Here we discuss possible applications of two emerging technologies to searches for physics beyond the Standard Model. First, laser frequency combs enable broad spectral coverage and coherent conversion between optical and RF signals. We are investigating tests of the nonminimal Standard-Model Extension using frequency combs coupled to broadband optical cavities. Second, nitrogen vacancy centers in diamond enable precision nanoscale magnetometry with applications from imaging to quantum science. We are investigating their use in searches for short-range spin-spin couplings.

  19. Optical Frequency Combs From Semiconductor Lasers and Applications in Ultrawideband Signal Processing and Communications

    NASA Astrophysics Data System (ADS)

    Delfyett, Peter J.; Gee, Sangyoun; Choi, Myoung-Taek; Izadpanah, Hossein; Lee, Wangkuen; Ozharar, Sarper; Quinlan, Franklyn; Yilmaz, Tolga

    2006-07-01

    Modelocked semiconductor lasers are used to generate a set of phase-locked optical frequencies on a periodic grid. The periodic and phase coherent nature of the optical frequency combs makes it possible for the realization of high-performance optical and RF arbitrary-waveform synthesis. In addition, the resulting optical frequency components can be used for communication applications relying on direct detection, dense wavelength division multiplexing (WDM), coherent-detection WDM, optical time-division multiplexing, and optical code division multiple access. This paper highlights the recent results in the use of optical frequency combs generated from semiconductors for ultrawideband signal processing and communication applications.

  20. Real-time dual-comb spectroscopy with a free-running bidirectionally mode-locked fiber laser

    NASA Astrophysics Data System (ADS)

    Mehravar, S.; Norwood, R. A.; Peyghambarian, N.; Kieu, K.

    2016-06-01

    Dual-comb technique has enabled exciting applications in high resolution spectroscopy, precision distance measurements, and 3D imaging. Major advantages over traditional methods can be achieved with dual-comb technique. For example, dual-comb spectroscopy provides orders of magnitude improvement in acquisition speed over standard Fourier-transform spectroscopy while still preserving the high resolution capability. Wider adoption of the technique has, however, been hindered by the need for complex and expensive ultrafast laser systems. Here, we present a simple and robust dual-comb system that employs a free-running bidirectionally mode-locked fiber laser operating at telecommunication wavelength. Two femtosecond frequency combs (with a small difference in repetition rates) are generated from a single laser cavity to ensure mutual coherent properties and common noise cancellation. As the result, we have achieved real-time absorption spectroscopy measurements without the need for complex servo locking with accurate frequency referencing, and relatively high signal-to-noise ratio.

  1. Doppler cooling with coherent trains of laser pulses and a tunable velocity comb

    SciTech Connect

    Ilinova, Ekaterina; Ahmad, Mahmoud; Derevianko, Andrei

    2011-09-15

    We explore the possibility of decelerating and Doppler cooling an ensemble of two-level atoms by a coherent train of short, nonoverlapping laser pulses. We derive analytical expressions for mechanical force exerted by the train. In frequency space the force pattern reflects the underlying frequency comb structure. The pattern depends strongly on the ratio of the atomic lifetime to the repetition time between the pulses and pulse area. For example, in the limit of short lifetimes, the frequency-space peaks of the optical force wash out. We propose to tune the carrier-envelope offset frequency to follow the Doppler-shifted detuning as atoms decelerate; this leads to compression of atomic velocity distribution about comb teeth and results in a ''velocity comb''--a series of narrow equidistant peaks in the velocity space.

  2. Solar radial velocity variations and the search for Venus enabled by a laser frequency comb

    NASA Astrophysics Data System (ADS)

    Phillips, David F.; Dumusque, Xavier; Li, Chih-Hao; Glenday, Alexander; Sasselov, Dimitar; Szentgyorgyi, Andrew; Walsworth, Ronald L.

    2016-05-01

    We have recently demonstrated 50 cm/s sensitivity in measuring the radial velocity (RV) between the Earth and Sun using a simple, compact solar telescope feeding the HARPS-N spectrograph at the Italian National Telescope calibrated with our green astro-comb. The green astro-comb is a laser frequency comb optimized for calibrating astrophysical spectrographs. We have been operating the solar telescope to detect the RV signal of the Sun as a star for the past year both to study RV jitter associated with stellar (solar) fluctuations and to demonstrate sensitivity of these instruments to detect terrestrial exoplanets. In this talk I will present results from calibrating the HARPS-N exoplanet searcher spectrograph, solar RV stability, and the current status of our search for the signature of Venus.

  3. FBG sensor system based on wavelength-swept active mode-locking laser with RSOA gain medium

    NASA Astrophysics Data System (ADS)

    Kim, Hyo-jin; Lee, Hwi Don; Jeong, Myong Yung; Kim, Chang-Seok; Lee, Ju Han

    2011-05-01

    We performed an experiment of wavelength-swept laser based on active mode-locking on reflective semiconductor optical amplifier (RSOA). Since this laser does not have a wavelength-selecting filter, it can achieve a high sweeping speed and reduce the component cost and size. Compared to the conventional SOA gain medium, RSOA shows a merit of higher efficiency of cross gain modulation due to the twice propagation of active gain region. We applied this laser to Fiber Bragg grating (FBG) strain sensor system which can have faster data acquisition speed than conventional wavelength-swept laser method. The linear response of FBG peak for the applied strain is monitored using the proposed laser source.

  4. Multimodal ophthalmic imaging using swept source spectrally encoded scanning laser ophthalmoscopy and optical coherence tomography

    NASA Astrophysics Data System (ADS)

    Malone, Joseph D.; El-Haddad, Mohamed T.; Tye, Logan A.; Majeau, Lucas; Godbout, Nicolas; Rollins, Andrew M.; Boudoux, Caroline; Tao, Yuankai K.

    2016-03-01

    Scanning laser ophthalmoscopy (SLO) and optical coherence tomography (OCT) benefit clinical diagnostic imaging in ophthalmology by enabling in vivo noninvasive en face and volumetric visualization of retinal structures, respectively. Spectrally encoding methods enable confocal imaging through fiber optics and reduces system complexity. Previous applications in ophthalmic imaging include spectrally encoded confocal scanning laser ophthalmoscopy (SECSLO) and a combined SECSLO-OCT system for image guidance, tracking, and registration. However, spectrally encoded imaging suffers from speckle noise because each spectrally encoded channel is effectively monochromatic. Here, we demonstrate in vivo human retinal imaging using a swept source spectrally encoded scanning laser ophthalmoscope and OCT (SSSESLO- OCT) at 1060 nm. SS-SESLO-OCT uses a shared 100 kHz Axsun swept source, shared scanner and imaging optics, and are detected simultaneously on a shared, dual channel high-speed digitizer. SESLO illumination and detection was performed using the single mode core and multimode inner cladding of a double clad fiber coupler, respectively, to preserve lateral resolution while improving collection efficiency and reducing speckle contrast at the expense of confocality. Concurrent en face SESLO and cross-sectional OCT images were acquired with 1376 x 500 pixels at 200 frames-per-second. Our system design is compact and uses a shared light source, imaging optics, and digitizer, which reduces overall system complexity and ensures inherent co-registration between SESLO and OCT FOVs. En face SESLO images acquired concurrent with OCT cross-sections enables lateral motion tracking and three-dimensional volume registration with broad applications in multivolume OCT averaging, image mosaicking, and intraoperative instrument tracking.

  5. A wavelength-tunable fiber laser based on a twin-core fiber comb filter

    NASA Astrophysics Data System (ADS)

    Zou, Hui; Lou, Shuqin; Yin, Guolu

    2013-02-01

    A wavelength-tunable fiber laser based on a twin-core fiber (TCF) comb filter is proposed and demonstrated. The TCF comb filter is fabricated by splicing a 0.85 m long TCF between two standard single mode fibers (SMFs) and with exhibits a good linear strain characteristic with a sensitivity of 1.23 pm/μɛ. The wavelength of the laser can be linearly tuned from 1558.04 nm to 1553.62 nm by applying an axial strain to the TCF comb filter. The optical signal-to-noise ratio (OSNR) of the fiber laser reaches 45 dB. The 3 dB bandwidth is 0.02 nm. The fluctuation of the laser peak in the output power and the wavelength is less than 0.5 dB and within 0.05 nm, respectively. The fiber laser has the advantages of having a simple structure and stable operation under room temperature.

  6. Real-Time Trace Gas Sensing of Fluorocarbons using a Swept-wavelength External Cavity Quantum Cascade Laser

    SciTech Connect

    Phillips, Mark C.; Taubman, Matthew S.; Bernacki, Bruce E.; Cannon, Bret D.; Stahl, Robert D.; Schiffern, John T.; Myers, Tanya L.

    2014-05-04

    We present results demonstrating real-time sensing of four different fluorocarbons at low-ppb concentrations using an external cavity quantum cascade laser (ECQCL) operating in a swept-wavelength configuration. The ECQCL was repeatedly swept over its full tuning range at a 20 Hz rate with a scan rate of 3535 cm-1/s, and a detailed characterization of the ECQCL scan stability and repeatability is presented. The sensor was deployed on a mobile automotive platform to provide spatially resolved detection of fluorocarbons in outdoor experiments. Noise-equivalent detection limits of 800-1000 parts-per-trillion (ppt) are demonstrated for 1 s integration times.

  7. Wavelength shifting of intra-cavity photons: Adiabatic wavelength tuning in rapidly wavelength-swept lasers.

    PubMed

    Jirauschek, Christian; Huber, Robert

    2015-07-01

    We analyze the physics behind the newest generation of rapidly wavelength tunable sources for optical coherence tomography (OCT), retaining a single longitudinal cavity mode during operation without repeated build up of lasing. In this context, we theoretically investigate the currently existing concepts of rapidly wavelength-swept lasers based on tuning of the cavity length or refractive index, leading to an altered optical path length inside the resonator. Specifically, we consider vertical-cavity surface-emitting lasers (VCSELs) with microelectromechanical system (MEMS) mirrors as well as Fourier domain mode-locked (FDML) and Vernier-tuned distributed Bragg reflector (VT-DBR) lasers. Based on heuristic arguments and exact analytical solutions of Maxwell's equations for a fundamental laser resonator model, we show that adiabatic wavelength tuning is achieved, i.e., hopping between cavity modes associated with a repeated build up of lasing is avoided, and the photon number is conserved. As a consequence, no fundamental limit exists for the wavelength tuning speed, in principle enabling wide-range wavelength sweeps at arbitrary tuning speeds with narrow instantaneous linewidth. PMID:26203373

  8. Wavelength shifting of intra-cavity photons: Adiabatic wavelength tuning in rapidly wavelength-swept lasers

    PubMed Central

    Jirauschek, Christian; Huber, Robert

    2015-01-01

    We analyze the physics behind the newest generation of rapidly wavelength tunable sources for optical coherence tomography (OCT), retaining a single longitudinal cavity mode during operation without repeated build up of lasing. In this context, we theoretically investigate the currently existing concepts of rapidly wavelength-swept lasers based on tuning of the cavity length or refractive index, leading to an altered optical path length inside the resonator. Specifically, we consider vertical-cavity surface-emitting lasers (VCSELs) with microelectromechanical system (MEMS) mirrors as well as Fourier domain mode-locked (FDML) and Vernier-tuned distributed Bragg reflector (VT-DBR) lasers. Based on heuristic arguments and exact analytical solutions of Maxwell’s equations for a fundamental laser resonator model, we show that adiabatic wavelength tuning is achieved, i.e., hopping between cavity modes associated with a repeated build up of lasing is avoided, and the photon number is conserved. As a consequence, no fundamental limit exists for the wavelength tuning speed, in principle enabling wide-range wavelength sweeps at arbitrary tuning speeds with narrow instantaneous linewidth. PMID:26203373

  9. Experimental investigation of a supersonic swept ramp injector using laser-induced iodine fluorescence

    NASA Technical Reports Server (NTRS)

    Hartfield, Roy J.; Hollo, Steven D.; Mcdaniel, James C.

    1990-01-01

    Planar measurements of injectant mole fraction and temperature have been conducted in a nonreacting supersonic combustor configured with underexpanded injection in the base of a swept ramp. The temperature measurements were conducted with a Mach 2 test section inlet in streamwise planes perpendicular to the test section wall on which the ramp was mounted. Injection concentration measurements, conducted in cross flow planes with both Mach 2 and Mach 2.9 free stream conditions, dramatically illustrate the domination of the mixing process by streamwise vorticity generated by the ramp. These measurements, conducted using a nonintrusive optical technique (laser-induced iodine fluorescence), provide an accurate and extensive experimental data base for the validation of computation fluid dynamic codes for the calculation of highly three-dimensional supersonic combustor flow fields.

  10. High-speed and long-time FBG interrogation system using wavelength swept laser

    NASA Astrophysics Data System (ADS)

    Yamaguchi, Tatsuya; Shinoda, Yukitaka

    2015-05-01

    The purpose of this research is the development of a system for fabricating high-speed and long-time measurements of wide-band vibration using fiber Bragg gratings (FBGs) to determine the health of structures. We developed a real-time FBG interrogation system using wavelength swept laser. This system can perform real-time measurement of reflected wavelength from a multiple FBG at a temporal resolution of 0.1 ms. The authors also constructed a database system for managing the data obtained from high-speed and long-time measurement. This database system manages data using a relational database and transfers information on FBG reflected wavelengths obtained from this measurement system via the local network. We have demonstrated that this system is able to measure reflected wavelengths from a multipoint FBG at a temporal resolution of 0.1 ms over 24 hours, it was shown that this system could also monitor instantaneously applied high-speed vibrations.

  11. Molecular fingerprinting with the resolved modes of a femtosecond laser frequency comb.

    PubMed

    Diddams, Scott A; Hollberg, Leo; Mbele, Vela

    2007-02-01

    The control of the broadband frequency comb emitted from a mode-locked femtosecond laser has permitted a wide range of scientific and technological advances--ranging from the counting of optical cycles for next-generation atomic clocks to measurements of phase-sensitive high-field processes. A unique advantage of the stabilized frequency comb is that it provides, in a single laser beam, about a million optical modes with very narrow linewidths and absolute frequency positions known to better than one part in 10(15) (ref. 5). One important application of this vast array of highly coherent optical fields is precision spectroscopy, in which a large number of modes can be used to map internal atomic energy structure and dynamics. However, an efficient means of simultaneously identifying, addressing and measuring the amplitude or relative phase of individual modes has not existed. Here we use a high-resolution disperser to separate the individual modes of a stabilized frequency comb into a two-dimensional array in the image plane of the spectrometer. We illustrate the power of this technique for high-resolution spectral fingerprinting of molecular iodine vapour, acquiring in a few milliseconds absorption images covering over 6 THz of bandwidth with high frequency resolution. Our technique for direct and parallel accessing of stabilized frequency comb modes could find application in high-bandwidth spread-spectrum communications with increased security, high-resolution coherent quantum control, and arbitrary optical waveform synthesis with control at the optical radian level. PMID:17287805

  12. Simultaneous low noise radio frequency tone and narrow linewidth optical comb generation from a regeneratively mode-locked laser

    NASA Astrophysics Data System (ADS)

    Ozdur, Ibrahim; Ozharar, Sarper; Delfyett, Peter J.

    2014-10-01

    A regeneratively mode-locked laser with simultaneous low noise radio frequency (RF) tone and optical comb generation is presented. The laser does not need any external RF signal and emits a pulse train at ˜10 GHz repetition rate with a 1.5-ps optical pulse width after compression. The generated RF tone has a signal-to-noise ratio of 121 dB/Hz and an RF fluctuation of 10-9 over 0.1 s. The optical frequency comb spacing is also at ˜10 GHz and the optical comb tooth has a linewidth of <1 kHz.

  13. Wide-bandwidth phase lock between a CW laser and a frequency comb based on a feed-forward configuration.

    PubMed

    Sala, T; Gatti, D; Gambetta, A; Coluccelli, N; Galzerano, G; Laporta, P; Marangoni, M

    2012-07-01

    Wide-bandwidth phase lock between the tooth of a frequency comb and a CW extended-cavity diode laser at 1.55 μm is achieved by the use of an acousto-optical frequency shifter in a feed-forward configuration. The coherence properties of the comb are efficiently transferred to the CW laser, whose linewidth is narrowed down to the ∼10 KHz comb level. A maximum control bandwidth of ∼0.6 MHz has been experimentally achieved, limited by the transit time of the acoustic wave inside the frequency shifter. PMID:22743465

  14. Phase-sensitive optical coherence tomography-based vibrometry using a highly phase-stable akinetic swept laser source

    SciTech Connect

    Applegate, Brian E.; Park, Jesung; Carbajal, Esteban; Oghalai, John S.

    2015-12-31

    Phase-sensitive Optical Coherence Tomography (PhOCT) is an emerging tool for in vivo investigation of the vibratory function of the intact middle and inner ear. PhOCT is able to resolve micron scale tissue morphology in three dimensions as well as measure picometer scale motion at each spatial position. Most PhOCT systems to date have relied upon the phase stability offered by spectrometer detection. On the other hand swept laser source based PhOCT offers a number of advantages including balanced detection, long imaging depths, and high imaging speeds. Unfortunately the inherent phase instability of traditional swept laser sources has necessitated complex user developed hardware/software solutions to restore phase sensitivity. Here we present recent results using a prototype swept laser that overcomes these issues. The akinetic swept laser is electronically tuned and precisely controls sweeps without any mechanical movement, which results in high phase stability. We have developed an optical fiber based PhOCT system around the akinetic laser source that had a 1550 nm center wavelength and a sweep rate of 140 kHz. The stability of the system was measured to be 4.4 pm with a calibrated reflector, thus demonstrating near shot noise limited performance. Using this PhOCT system, we have acquired structural and vibratory measurements of the middle ear in a mouse model, post mortem. The quality of the results suggest that the akinetic laser source is a superior laser source for PhOCT with many advantages that greatly reduces the required complexity of the imaging system.

  15. Phase-sensitive optical coherence tomography-based vibrometry using a highly phase-stable akinetic swept laser source

    NASA Astrophysics Data System (ADS)

    Applegate, Brian E.; Park, Jesung; Carbajal, Esteban; Oghalai, John S.

    2015-12-01

    Phase-sensitive Optical Coherence Tomography (PhOCT) is an emerging tool for in vivo investigation of the vibratory function of the intact middle and inner ear. PhOCT is able to resolve micron scale tissue morphology in three dimensions as well as measure picometer scale motion at each spatial position. Most PhOCT systems to date have relied upon the phase stability offered by spectrometer detection. On the other hand swept laser source based PhOCT offers a number of advantages including balanced detection, long imaging depths, and high imaging speeds. Unfortunately the inherent phase instability of traditional swept laser sources has necessitated complex user developed hardware/software solutions to restore phase sensitivity. Here we present recent results using a prototype swept laser that overcomes these issues. The akinetic swept laser is electronically tuned and precisely controls sweeps without any mechanical movement, which results in high phase stability. We have developed an optical fiber based PhOCT system around the akinetic laser source that had a 1550 nm center wavelength and a sweep rate of 140 kHz. The stability of the system was measured to be 4.4 pm with a calibrated reflector, thus demonstrating near shot noise limited performance. Using this PhOCT system, we have acquired structural and vibratory measurements of the middle ear in a mouse model, post mortem. The quality of the results suggest that the akinetic laser source is a superior laser source for PhOCT with many advantages that greatly reduces the required complexity of the imaging system.

  16. Impact of dispersion on amplitude and frequency noise in a Yb-fiber laser comb.

    PubMed

    Nugent-Glandorf, Lora; Johnson, Todd A; Kobayashi, Yohei; Diddams, Scott A

    2011-05-01

    We describe a Yb-fiber-based laser comb, with a focus on the relationship between the net-cavity dispersion and frequency noise on the comb. While tuning the net-cavity dispersion from anomalous to normal, we measure the relative intensity noise, offset frequency (f(CEO)) linewidth, and the resulting frequency noise spectrum on the f(CEO). We find that the laser operating at zero net-cavity dispersion has many advantages, including an approximately 100× reduction in free-running f(CEO) linewidth and frequency noise power spectral density when compared to the normal-dispersion regime. At the zero-dispersion point, we demonstrate a phase-locked f(CEO) beat with low residual noise. PMID:21540933

  17. Laser Frequency Comb Supported Stellar Radial Velocity Determination in the NIR: Initial Results.

    NASA Astrophysics Data System (ADS)

    Osterman, Steve; Diddams, S.; Quinlan, F.; Ycas, G.; Mahadevan, S.; Ramsey, L.; Bender, C.; Terrien, R.; Botzer, B.; Redman, S.

    2011-09-01

    The laser frequency comb presents the potential for a revolutionary increase in radial velocity precision by providing a calibration reference of unprecedented quality in terms of wavelength knowledge, repeatability, number, density and regularity of lines. Promising first steps have been taken leading to the derivation of stellar radial velocities in the NIR H band, a wavelength range well suited to the observation of M dwarfs. These stars, with low mass and low luminosity, are the most prevalent class of stars within 10 parsecs and can be expected to yield a higher reflex velocity for a terrestrial mass planet in the liquid water habitable zone than would be the case with a more massive star such as our own. We present the design and both laboratory and on-sky performance of an H-band laser frequency comb used in conjunction with the Penn State Pathfinder testbed spectrograph and discuss lessons learned and plans for follow on testing.

  18. Performance of a laser frequency comb calibration system with a high-resolution solar echelle spectrograph

    NASA Astrophysics Data System (ADS)

    Doerr, H.-P.; Kentischer, T. J.; Steinmetz, T.; Probst, R. A.; Franz, M.; Holzwarth, R.; Udem, Th.; Hänsch, T. W.; Schmidt, W.

    2012-09-01

    Laser frequency combs (LFC) provide a direct link between the radio frequency (RF) and the optical frequency regime. The comb-like spectrum of an LFC is formed by exact equidistant laser modes, whose absolute optical frequencies are controlled by RF-references such as atomic clocks or GPS receivers. While nowadays LFCs are routinely used in metrological and spectroscopic fields, their application in astronomy was delayed until recently when systems became available with a mode spacing and wavelength coverage suitable for calibration of astronomical spectrographs. We developed a LFC based calibration system for the high-resolution echelle spectrograph at the German Vacuum Tower Telescope (VTT), located at the Teide observatory, Tenerife, Canary Islands. To characterize the calibration performance of the instrument, we use an all-fiber setup where sunlight and calibration light are fed to the spectrograph by the same single-mode fiber, eliminating systematic effects related to variable grating illumination.

  19. Resonant light scattering of a laser frequency comb by a quantum dot

    NASA Astrophysics Data System (ADS)

    Konthasinghe, K.; Peiris, M.; Muller, A.

    2014-08-01

    We investigate the spectral and temporal properties of light scattered near resonantly by a single quantum dot when the incident laser field is a frequency comb consisting of a superposition of monochromatic waves equidistant in frequency. Such fields encompass those generated by, e.g., a periodically pulsed laser. A general theoretical treatment for the calculation of first- and second-order correlation functions is given which takes account of spectral diffusion through a slowly varying detuning from resonance, permitting accurate comparison with experiments. We explore the two distinct regimes in which the frequency-comb separation is either larger or smaller than the radiative decay rate. We verify the validity of our calculations by a comparison with experimental data for the case of a bichromatic field and discuss the manifestation of phase coherence between the incoming field and the scattered single-photon wave packet.

  20. High-speed dispersion-tuned wavelength-swept fiber laser using a reflective SOA and a chirped FBG.

    PubMed

    Takubo, Yuya; Yamashita, Shinji

    2013-02-25

    We present a high-speed wavelength-swept fiber laser based on a dispersion tuning method using a reflective semiconductor optical amplifier (RSOA) and a chirped fiber Bragg grating (CFBG). By using these devices, the cavity length can be shortened drastically. The short cavity improves the laser performance at high sweep rates over 200 kHz. We achieve a sweep range of 60 nm and an output power of 8.4 mW at 100 kHz sweep. We applied the dispersion-tuned fiber laser to the swept-source OCT system and successfully obtained OCT images of an adhesive tape at up to 250 kHz sweep rate. PMID:23482047

  1. A Fiber Bragg Grating Sensor Interrogation System Based on a Linearly Wavelength-Swept Thermo-Optic Laser Chip

    PubMed Central

    Lee, Hyung-Seok; Lee, Hwi Don; Kim, Hyo Jin; Cho, Jae Du; Jeong, Myung Yung; Kim, Chang-Seok

    2014-01-01

    A linearized wavelength-swept thermo-optic laser chip was applied to demonstrate a fiber Bragg grating (FBG) sensor interrogation system. A broad tuning range of 11.8 nm was periodically obtained from the laser chip for a sweep rate of 16 Hz. To measure the linear time response of the reflection signal from the FBG sensor, a programmed driving signal was directly applied to the wavelength-swept laser chip. The linear wavelength response of the applied strain was clearly extracted with an R-squared value of 0.99994. To test the feasibility of the system for dynamic measurements, the dynamic strain was successfully interrogated with a repetition rate of 0.2 Hz by using this FBG sensor interrogation system. PMID:25177803

  2. A near infrared laser frequency comb for high precision Doppler planet surveys

    NASA Astrophysics Data System (ADS)

    Osterman, S.; Diddams, S.; Quinlan, F.; Bally, J.; Ge, J.; Ycas, G.

    2011-07-01

    Perhaps the most exciting area of astronomical research today is the study of exoplanets and exoplanetary systems, engaging the imagination not just of the astronomical community, but of the general population. Astronomical instrumentation has matured to the level where it is possible to detect terrestrial planets orbiting distant stars via radial velocity (RV) measurements, with the most stable visible light spectrographs reporting RV results the order of 1 m/s. This, however, is an order of magnitude away from the precision needed to detect an Earth analog orbiting a star such as our sun, the Holy Grail of these efforts. By performing these observations in near infrared (NIR) there is the potential to simplify the search for distant terrestrial planets by studying cooler, less massive, much more numerous class M stars, with a tighter habitable zone and correspondingly larger RV signal. This NIR advantage is undone by the lack of a suitable high precision, high stability wavelength standard, limiting NIR RV measurements to tens or hundreds of m/s [1, 2]. With the improved spectroscopic precision provided by a laser frequency comb based wavelength reference producing a set of bright, densely and uniformly spaced lines, it will be possible to achieve up to two orders of magnitude improvement in RV precision, limited only by the precision and sensitivity of existing spectrographs, enabling the observation of Earth analogs through RV measurements. We discuss the laser frequency comb as an astronomical wavelength reference, and describe progress towards a near infrared laser frequency comb at the National Institute of Standards and Technology and at the University of Colorado where we are operating a laser frequency comb suitable for use with a high resolution H band astronomical spectrograph.

  3. TECHNICAL NOTE: Development of fiber Bragg grating sensor system using wavelength-swept fiber laser

    NASA Astrophysics Data System (ADS)

    Ryu, Chi-Young; Hong, Chang-Sun

    2002-06-01

    Fiber Bragg grating (FBG) sensors based on the wavelength division multiplexing technology are ideally suited for structural health monitoring. In many applications, it is desirable to form several arrays of optical fiber sensors to monitor the response of structures. In the present study, we constructed an improved FBG sensor system using a wavelength-swept fiber laser which exhibits high output power for several sensor arrays. A fiber cavity etalon was also fabricated for the calibration of the nonlinear output wavelength of a laser and for scaling the information in the wavelength domain for signal processing. The constructed FBG sensor system with the fiber cavity etalon and a reference FBG was applied for strain measurements of a laminated composite panel under axial compressive loading. In order to monitor the structural strain in real time, the signal-processing program was constructed using LabVIEW software for storing and visualizing data from the FBG sensors. Experiments showed that the constructed FBG sensor system and the real-time signal-processing program could successfully monitor the strain of composite laminates. This improved FBG sensor system could be useful for large structures which require a large number of sensor arrays.

  4. Characterization of wavelength-swept active mode locking fiber laser based on reflective semiconductor optical amplifier

    NASA Astrophysics Data System (ADS)

    Lee, Hwi Don; Lee, Ju Han; Yung Jeong, Myung; Kim, Chang-Seok

    2011-07-01

    The static and dynamic characteristics of a wavelength-swept active mode locking (AML) fiber laser are presented in both the time-region and wavelength-region. This paper shows experimentally that the linewidth of a laser spectrum and the bandwidth of the sweeping wavelength are dependent directly on the length and dispersion of the fiber cavity as well as the modulation frequency and sweeping rate under the mode-locking condition. To achieve a narrower linewidth, a longer length and higher dispersion of the fiber cavity as well as a higher order mode locking condition are required simultaneously. For a broader bandwidth, a lower order of the mode locking condition is required using a lower modulation frequency. The dynamic sweeping performance is also analyzed experimentally to determine its applicability to optical coherence tomography imaging. It is shown that the maximum sweeping rate can be improved by the increased free spectral range from the shorter length of the fiber cavity. A reflective semiconductor optical amplifier (RSOA) was used to enhance the modulation and dispersion efficiency. Overall a triangular electrical signal can be used instead of the sinusoidal signal to sweep the lasing wavelength at a high sweeping rate due to the lack of mechanical restrictions in the wavelength sweeping mechanism.

  5. Frequency Combs

    NASA Astrophysics Data System (ADS)

    Hänsch, Theodor W.; Picqué, Nathalie

    Much of modern research in the field of atomic, molecular, and optical science relies on lasers, which were invented some 50 years ago and perfected in five decades of intense research and development. Today, lasers and photonic technologies impact most fields of science and they have become indispensible in our daily lives. Laser frequency combs were conceived a decade ago as tools for the precision spectroscopy of atomic hydrogen. Through the development of optical frequency comb techniques, technique a setup of the size 1 ×1 m2, good for precision measurements of any frequency, and even commercially available, has replaced the elaborate previous frequency-chain schemes for optical frequency measurements, which only worked for selected frequencies. A true revolution in optical frequency measurements has occurred, paving the way for the creation of all-optical clocks clock with a precision that might approach 10-18. A decade later, frequency combs are now common equipment in all frequency metrology-oriented laboratories. They are also becoming enabling tools for an increasing number of applications, from the calibration of astronomical spectrographs to molecular spectroscopy. This chapter first describes the principle of an optical frequency comb synthesizer. Some of the key technologies to generate such a frequency comb are then presented. Finally, a non-exhaustive overview of the growing applications is given.

  6. >400 kHz repetition rate wavelength-swept laser and application to high-speed optical frequency domain imaging

    PubMed Central

    Oh, Wang-Yuhl; Vakoc, Benjamin J.; Shishkov, Milen; Tearney, Guillermo J.; Bouma, Brett E.

    2010-01-01

    We demonstrate a high-speed wavelength-swept laser with a tuning range of 104 nm (1228–1332 nm) and a repetition rate of 403 kHz. The design of the laser utilizes a high-finesse polygon-based wavelength-scanning filter and a short-length unidirectional ring resonator. Optical frequency domain imaging of the human skin in vivo is presented using this laser, and the system shows sensitivity of higher than 98 dB with single-side ranging depth of 1.7 mm over 4 dB sensitivity roll-off. PMID:20808369

  7. Spectral-domain OCT imaging using a spectrally flexible wavelength-swept fiber laser based on dispersion tuning

    NASA Astrophysics Data System (ADS)

    Takubo, Y.; Yamashita, S.

    2014-05-01

    The broadband source with the arbitrary spectrum based on dispersion tuning technique was demonstrated. While a dispersion-tuned wavelength-swept laser is capable of fast and widely wavelength sweep, it can also be used as a broadband spectrally-flexible source by controlling the sweep waveform. It is the first demonstration of spectrallytunable source to the best of our knowledge. We used the dispersion-tuned laser as a broadband source for SD-OCT system by synchronizing sweep rate of a laser and exposure time of a CCD camera in SD-OCT system. We successfully obtained the images of an adhesive tape and a human finger.

  8. Stellar radial velocities using a laser frequency comb: Application and observations in the near infrared

    NASA Astrophysics Data System (ADS)

    Osterman, Steve

    2011-04-01

    The laser frequency comb presents the potential for a revolutionary increase in radial velocity precision by providing a calibration reference of unprecedented quality in terms of wavelength knowledge, repeatability, number, density, and regularity of lines. However, implementation has proven challenging, particularly in the near infrared. Nevertheless, with the right combination of comb and instrument, promising first steps have been taken, allowing for the derivation of stellar radial velocities in a wavelength range which is well suited to the observation of M dwarfs. These stars, with low mass and low luminosity, are the most prevalent class of stars within 10 parsecs and can be expected to yield a higher reflex velocity for a terrestrial mass planet in the liquid water habitable zone than would be the case with a more massive star such as our own. We present the design and both laboratory and on-sky performance of an H-band laser frequency comb used in conjunction with the Penn State Pathfinder testbed spectrograph and discuss lessons learned and plans for follow on testing with both the Pathfinder and the CSHELL instruments.

  9. A rapid, dispersion-based wavelength-stepped and wavelength-swept laser for optical coherence tomography

    PubMed Central

    Tozburun, Serhat; Siddiqui, Meena; Vakoc, Benjamin J.

    2014-01-01

    Abstract: Optical-domain subsampling enables Fourier-domain OCT imaging at high-speeds and extended depth ranges while limiting the required acquisition bandwidth. To perform optical-domain subsampling, a wavelength-stepped rather than a wavelength-swept source is required. This preliminary study introduces a novel design for a rapid wavelength-stepped laser source that uses dispersive fibers in combination with a fast lithium-niobate modulator to achieve wavelength selection. A laser with 200 GHz wavelength-stepping and a sweep rate of 9 MHz over a 94 nm range at a center wavelength of 1550 nm is demonstrated. A reconfiguration of this source design to a continuous wavelength-swept light for conventional Fourier-domain OCT is also demonstrated. PMID:24663631

  10. First Stellar Radial Velocities with a Laser Frequency Comb: Observations in the NIR H Band

    NASA Astrophysics Data System (ADS)

    Osterman, Steve; Diddams, S.; Quinlan, F.; Ycas, G.; Mahadevan, S.; Ramsey, L.; Bender, C.; Redman, S.; Terrien, R.; Botzer, B.

    2011-01-01

    Advances in high precision radial velocity spectroscopy have been hindered by the lack of suitable wavelength references. This has been especially the case in the infrared where until recently radial velocity precision has been limited to 50-100m/s, hindering investigations such as the search for extrasolar planets orbiting cooler M stars at these wavelengths. To redress deficiency this we have developed a 25GHz laser frequency comb spanning the H band and suitable for use with spectrographs with spectral resolution in the range of 40,000 - 60,000, with RV precision limited by instrument stability and object S/N rather than by the lack of a suitable wavelength standard. We will present CU/NIST frequency comb performance and results obtained using the Pennsylvania State University's Pathfinder Spectrograph on the Hobby Eberly Telescope and will discuss lessons learned.

  11. A Laser Frequency Comb System for Absolute Calibration of the VTT Echelle Spectrograph

    NASA Astrophysics Data System (ADS)

    Doerr, H.-P.; Steinmetz, T.; Holzwarth, R.; Kentischer, T.; Schmidt, W.

    2012-10-01

    A wavelength calibration system based on a laser frequency comb (LFC) was developed in a co-operation between the Kiepenheuer-Institut für Sonnenphysik, Freiburg, Germany and the Max-Planck-Institut für Quantenoptik, Garching, Germany for permanent installation at the German Vacuum Tower Telescope (VTT) on Tenerife, Canary Islands. The system was installed successfully in October 2011. By simultaneously recording the spectra from the Sun and the LFC, for each exposure a calibration curve can be derived from the known frequencies of the comb modes that is suitable for absolute calibration at the meters per second level. We briefly summarize some topics in solar physics that benefit from absolute spectroscopy and point out the advantages of LFC compared to traditional calibration techniques. We also sketch the basic setup of the VTT calibration system and its integration with the existing echelle spectrograph.

  12. Frequency comb offset dynamics of SESAM modelocked thin disk lasers.

    PubMed

    Emaury, Florian; Diebold, Andreas; Klenner, Alexander; Saraceno, Clara J; Schilt, Stéphane; Südmeyer, Thomas; Keller, Ursula

    2015-08-24

    We present a detailed study of the carrier-envelope offset (CEO) frequency dynamics of SESAM modelocked thin disk lasers (TDLs) pumped by kW-class highly transverse multimode pump diodes with a typical M(2) value of 200-300, and give guidelines for future frequency stabilization of multi-100-W oscillators. We demonstrate CEO frequency detection with > 30 dB signal-to-noise ratio with a resolution bandwidth of 100 kHz from a SESAM modelocked Yb:YAG TDL delivering 140 W average output power with 748-fs pulses at 7-MHz pulse repetition rate. We compare with a low-power CEO frequency stabilized Yb:CALGO TDL delivering 2.1 W with 77-fs pulses at 65 MHz. For both lasers, we perform a complete noise characterization, measure the relevant transfer functions (TFs) and compare them to theoretical models. The measured TFs are used to determine the propagation of the pump noise step-by-step through the system components. From the noise propagation analysis, we identify the relative intensity noise (RIN) of the pump diode as the main contribution to the CEO frequency noise. The resulting noise levels are not excessive and do not prevent CEO frequency stabilization. More importantly, the laser cavity dynamics are shown to play an essential role in the CEO frequency dynamics. The cavity TFs of the two lasers are very different which explains why at this point a tight CEO frequency lock can be obtained with the Yb:CALGO TDL but not with the Yb:YAG TDL. For CEO stabilization laser cavities should exhibit high damping of the relaxation oscillations by nonlinear intra-cavity elements, for example by operating a SESAM in the roll-over regime. Therefore the optimum SESAM operation point is a trade-off between enough damping and avoiding multiple pulsing instabilities. Additional cavity components could be considered for supplementary damping independent of the SESAM operation point. PMID:26368160

  13. Wavelength-swept lasers and their application to fiber optic sensors

    NASA Astrophysics Data System (ADS)

    Jeon, Min Yong; Ko, Myeong Ock; Choi, Byeong Kwon; Kwon, Yong Seok

    2014-10-01

    The wavelength swept laser (WSL) is a promising optical source in optical coherence tomography, optical fiber sensor, and optical beat source generation. It is demonstrated by employing a narrowband wavelength-scanning filter, such as a fast rotating polygonal-scanner-filter, a diffraction grating on a galvo-scan mirror, or a fiber Fabry-Perot tunable filter (FFP-TF). In this manuscript, we present our researches on the dynamic fiber-optic sensors. Two kinds of WSLs are used to demonstrate the dynamic measurement in the fiber-optic sensors. One is the WSL using a polygon-scanner-based wavelength filter and the other is the Fourier domain mode-locked (FDML) WSL using a FFP-TF. The dynamic fiber Bragg grating (FBG) sensor interrogation up to 2 kHz by using the WSL with a polygonscanner- based wavelength filter is reported. And by using the FDML WSL with a FFP-TF, we demonstrate a resonance FBG sensor interrogation. As another application of the WSL, we successfully measure a dynamic modulation frequency of the applied electric field using a nematic liquid crystal Fabry-Perot etalon.

  14. Characterization of a swept external cavity quantum cascade laser for rapid broadband spectroscopy and sensing.

    PubMed

    Brumfield, Brian E; Taubman, Matthew S; Suter, Jonathan D; Phillips, Mark C

    2015-10-01

    The performance of a rapidly swept external cavity quantum cascade laser (ECQCL) system combined with an open-path Herriott cell was evaluated for time-resolved measurements of chemical species with broad and narrow absorption spectra. A spectral window spanning 1278 - 1390 cm(-1) was acquired at a 200 Hz acquisition rate, corresponding to a tuning rate of 2x10(4) cm(-1)/s, with a spectral resolution of 0.2 cm(-1). The capability of the ECQCL to measure < 100 ppbv changes in nitrous oxide (N(2)O) and 1,1,1,2-tetrafluoroethane (F134A) concentrations on millisecond timescales was demonstrated in simulated plume studies with releases near the open-path Herriott cell. Absorbance spectra measured using the ECQCL system exhibited noise-equivalent absorption coefficients of 5x10(-9) cm(-1)Hz(-1/2). For a spectrum acquisition time of 5 ms, noise-equivalent concentrations (NEC) for N(2)O and F134A were measured to be 70 and 16 ppbv respectively, which improved to sub-ppbv levels with averaging to 100 s. Noise equivalent column densities of 0.64 and 0.25 ppmv × m in 1 sec are estimated for N(2)O and F134A. PMID:26480072

  15. Dynamic Sensor Interrogation Using Wavelength-Swept Laser with a Polygon-Scanner-Based Wavelength Filter

    PubMed Central

    Kwon, Yong Seok; Ko, Myeong Ock; Jung, Mi Sun; Park, Ik Gon; Kim, Namje; Han, Sang-Pil; Ryu, Han-Cheol; Park, Kyung Hyun; Jeon, Min Yong

    2013-01-01

    We report a high-speed (∼2 kHz) dynamic multiplexed fiber Bragg grating (FBG) sensor interrogation using a wavelength-swept laser (WSL) with a polygon-scanner-based wavelength filter. The scanning frequency of the WSL is 18 kHz, and the 10 dB scanning bandwidth is more than 90 nm around a center wavelength of 1,540 nm. The output from the WSL is coupled into the multiplexed FBG array, which consists of five FBGs. The reflected Bragg wavelengths of the FBGs are 1,532.02 nm, 1,537.84 nm, 1,543.48 nm, 1,547.98 nm, and 1,553.06 nm, respectively. A dynamic periodic strain ranging from 500 Hz to 2 kHz is applied to one of the multiplexed FBGs, which is fixed on the stage of the piezoelectric transducer stack. Good dynamic performance of the FBGs and recording of their fast Fourier transform spectra have been successfully achieved with a measuring speed of 18 kHz. The signal-to-noise ratio and the bandwidth over the whole frequency span are determined to be more than 30 dB and around 10 Hz, respectively. We successfully obtained a real-time measurement of the abrupt change of the periodic strain. The dynamic FBG sensor interrogation system can be read out with a WSL for high-speed and high-sensitivity real-time measurement. PMID:23899934

  16. A Y+J Band Laser Frequency Comb for the Habitable Zone Planet Finder

    NASA Astrophysics Data System (ADS)

    Osterman, Steve; Ycas, G. G.; Diddams, S. A.; Bender, C. F.; Donaldson, C. L.; Mahadevan, S.; Quinlan, F.; Ramsey, L. W.

    2013-01-01

    The Habitable Zone Planet Finder (HPF) scheduled for deployment to the Hobby-Eberly Telescope in late 2015 will extend the radial velocity search for exoplanets into the near infrared by providing a high precision, stabilized near infrared spectrograph spanning the Y+J bands (0.98-1.3μm) with 50,000 resolution. Working in the near infrared will allow the HPF to study cooler, lower mass stars than is possible with the current generation of optical spectrographs. In order to extend the precision of the HPF to lower minimum RV signatures we are proposing to develop a deployable, fully autonomous version of the Y+J band laser frequency comb currently in operation at the NIST Time and Frequency Division in Boulder, Colorado. The Y+J comb is derived from the H band (1.45-1.7μm) comb which was successfully demonstrated at the Hobby-Eberly Telescope in 2010. The deployed version will leverage off of existing hardware and demonstrated technology. We present instrument architecture and current performance as well as results of long term stability tests, filter modeling, modal noise reduction results and predicted end-to-end performance.

  17. From a discrete to a continuous model for interpulse interference with a frequency-comb laser

    SciTech Connect

    Zeitouny, M. G.; Cui, M.; Bhattacharya, N.; Urbach, H. P.; Berg, S. A. van den; Janssen, A. J. E. M.

    2010-08-15

    We have investigated correlation patterns generated by a frequency-comb laser in a dispersive unbalanced Michelson interferometer and apply the developed formalism to the case of distance metrology. Due to group velocity dispersion, the position of the brightest fringe of the correlation pattern, which is used for distance determination, cannot be derived by simply using the definition of group refractive index of the dispersive medium. It is shown that the discrete spectrum of the optical frequency comb gives rise to correlation functions which can be represented by a series, namely a discrete correlation series. We have developed a general formalism, valid for any pulse train, extending the discrete model to a continuous model of cross-correlation functions using the Poisson summation. Our model is relevant for any offset and repetition frequency of the frequency comb. From the continuous cross-correlation model we show that, even for a homogeneous dispersive medium the position of the brightest fringe varies nonlinearly for small delay distances and stabilizes for longer ones. We have compared the theoretical results to measurements of pulse propagation in air for path-lengths up to 200 m.

  18. Comb-calibrated frequency-modulated continuous-wave ladar for absolute distance measurements.

    PubMed

    Baumann, Esther; Giorgetta, Fabrizio R; Coddington, Ian; Sinclair, Laura C; Knabe, Kevin; Swann, William C; Newbury, Nathan R

    2013-06-15

    We demonstrate a comb-calibrated frequency-modulated continuous-wave laser detection and ranging (FMCW ladar) system for absolute distance measurements. The FMCW ladar uses a compact external cavity laser that is swept quasi-sinusoidally over 1 THz at a 1 kHz rate. The system simultaneously records the heterodyne FMCW ladar signal and the instantaneous laser frequency at sweep rates up to 3400 THz/s, as measured against a free-running frequency comb (femtosecond fiber laser). Demodulation of the ladar signal against the instantaneous laser frequency yields the range to the target with 1 ms update rates, bandwidth-limited 130 μm resolution and a ~100 nm accuracy that is directly linked to the counted repetition rate of the comb. The precision is <100 nm at the 1 ms update rate and reaches ~6 nm for a 100 ms average. PMID:23938965

  19. Tuneable dual-comb spectrometer based on commercial femtosecond lasers and reference cell for optical frequency calibration

    NASA Astrophysics Data System (ADS)

    Portuondo-Campa, E.; Bennès, J.; Balet, L.; Kundermann, S.; Merenda, F.; Boer, G.; Lecomte, S.

    2016-07-01

    Two commercial femtosecond laser sources have been used to implement a dual-comb spectrometer tuneable across a spectral range from 1.5 to 2.2 μm. The optical linewidth of the comb modes was characterized for different time scales in order to estimate the achievable spectral resolution for an optimal acquisition time. The transmission spectra of three different gas samples were recorded, demonstrating good agreement with reference data. Frequency axis calibration was provided via the parallel monitoring of a reference sample. This technique allows an accurate calibration of the frequency axis of the spectrometer, with no need for stabilization or optical referencing of the frequency combs. Our set-up represents a good compromise for a compact and versatile dual-comb spectrometer based on commercially available parts with possible applications in trace-gas monitoring, remote sensing and spectroscopy of short-lived processes.

  20. Generation of optical frequency combs in a fiber-ring/microresonator laser system.

    PubMed

    Guo, Changlei; Che, Kaijun; Xu, Huiying; Zhang, Pan; Tang, Deyu; Ren, Changyan; Luo, Zhengqian; Cai, Zhiping

    2016-06-01

    We propose and experimentally demonstrate a simple scheme for generating optical frequency combs (OFCs) in a fiber-ring/microresonator laser system. The ultrahigh Q whispering gallery mode microresonator is employed both as a mode reflection mirror to generate erbium lasing and as a Kerr-nonlinearity initiator that introduces optical parametric oscillation signals to form OFCs. By controlling the coupling position between the fiber taper and microresonator, optimizing the fiber polarization, as well as the pump power from a 974 nm laser diode (LD), versatile OFCs can be tuned out from single-wavelength states. The OFCs have single, multiple, or combined free spectral ranges. In addition, a Raman-gain-assisted OFC is also observed with a bandwidth of ∼230  nm. This LD-pumped and multifunctional laser system could find applications in precision spectroscopy, biochemical sensing, and optical fiber communication systems. PMID:27244418

  1. Developing Stabilized Lasers, Measuring their Frequencies, demoting the Metre, inventing the Comb, and further consequences

    NASA Astrophysics Data System (ADS)

    Hall, John L.

    2010-02-01

    Michelson's 1907 proposal to define the SI Metre in terms of an optical wavelength was realized only in 1960, based on a ^86Krypton discharge lamp. The same year saw the cw HeNe laser arrive and a future redefinition based on laser technology assured. Separation in the late 60's of the laser's gain and spectral-reference-gas functions led to unprecedented levels of laser frequency stability and reproducibility. In addition to HeNe:CH4 system at 3392 nm and HeNe:I2 at 633 nm, systems at 514 nm and 10600 nm were studied. Absolute frequency measurement became the holy grail and some NBS team experiences will be shared. We measured both frequency and wavelength in 1972, and so obtained a speed of light value, improved 100-fold in accuracy. During the next decade, the NBS value of c was confirmed by other national labs, and frequency metrology was extended to the 473 THz (633 nm) Iodine-based wavelength standard. This frequency to ˜10 digit accuracy was obtained in 1983, thus setting the stage for redefining the SI Metre. By consensus choice the value 299 792 458 m/s was adopted for the speed of light, effectively reducing the Metre to a derived SI quantity. Knowledge of the frequency of the particular laser being utilized was controlled by International intercomparisons, but the need for a fast and accurate means to make these laser frequency measurements was obvious. Creative proposals by H"ansch and by Chebotayev were to use ultra-fast repetitive pulses to create an ``Optical Comb,'' but it was years before any technical basis existed to implement their Fourier dreams. Finally, in 1999 the last needed capability was demonstrated -- continuum production at 100 MHz rates and non-destructive power levels. By May 2000 phase-locked combs were operational in both Garching and Boulder, substantially accelerated by their collaborative interactions. Within 18 months all the known proposed ``optical frequency standards'' had been accurately measured via Comb techniques. )

  2. The AC-Stark Effect in Nitric Oxide Induced by Rapidly Swept Continuous Wave Quantum Cascade Lasers

    SciTech Connect

    Duxbury, Geoffrey; Kelly, James F.; Blake, Thomas A.; Langford, Nigel

    2012-05-07

    A large AC Stark effect has been observed when nitric oxide, at low pressure in a long optical path (100 m) Herriot cell, is subjected to infrared radiation from a rapidly swept, continuous wave infrared quantum cascade laser. As the frequency sweep rate of the laser is increased, an emission signal induced by rapid passage, occurs after the laser frequency has passed through the resonance of a molecular absorption line. At very high sweep rates a laser field-induced splitting of the absorptive part of the signal is observed, due to the AC Stark effect. This splitting is related to the Autler-Townes mixing of the hyperfine transitions, which lie within the lambda doublet components of the transition, under the Doppler broadened envelope.

  3. Narrow linewidth laser system realized by linewidth transfer using a fiber-based frequency comb for the magneto-optical trapping of strontium.

    PubMed

    Akamatsu, Daisuke; Nakajima, Yoshiaki; Inaba, Hajime; Hosaka, Kazumoto; Yasuda, Masami; Onae, Atsushi; Hong, Feng-Lei

    2012-07-01

    A narrow linewidth diode laser system at 689 nm is realized by phase-locking an extended cavity diode laser to one tooth of a narrow linewidth optical frequency comb. The optical frequency comb is phase-locked to a narrow linewidth laser at 1064 nm, which is frequency stabilized to a high-finesse optical cavity. We demonstrate the magneto-optical trapping of Sr using an intercombination transition with the developed laser system. PMID:22772290

  4. Monolithic CEO-stabilization scheme-based frequency comb from an octave-spanning laser

    NASA Astrophysics Data System (ADS)

    Zi-Jiao, Yu; Hai-Nian, Han; Yang, Xie; Hao, Teng; Zhao-Hua, Wang; Zhi-Yi, Wei

    2016-04-01

    We demonstrate a carrier-envelope phase-stabilized octave-spanning oscillator based on the monolithic scheme. A wide output spectrum extending from 480 nm to 1050 nm was generated directly from an all-chirped mirror Ti:sapphire laser. After several improvements, the carrier-envelope offset (CEO) beat frequency accessed nearly 60 dB under a resolution of 100 kHz. Using a feedback system with 50-kHz bandwidth, we compressed the residual phase noise to 55 mrad (integrated from 1 Hz to 1 MHz) for the stabilized CEO, corresponding to 23-as timing jitter at the central wavelength of 790 nm. This is, to the best of our knowledge, the smallest timing jitter achieved among the existing octave-spanning laser based frequency combs. Project supported by the National Basic Research Program of China (Grant No. 2012CB821304) and the National Natural Science Foundation of China (Grant Nos. 11078022 and 61378040).

  5. Self-similar pulse evolution in a fiber laser with a comb-like dispersion-decreasing fiber.

    PubMed

    Tang, Yuxing; Liu, Zhanwei; Fu, Walter; Wise, Frank W

    2016-05-15

    We demonstrate an erbium fiber laser with self-similar pulse evolution inside a comb-like dispersion-decreasing fiber. We show numerically and experimentally that the comb-like dispersion-decreasing fiber works as well as an ideal one, and offers major practical advantages. The existence of a nonlinear attractor is verified by the invariant pulse chirp over a wide range of net cavity dispersion in experiments. The laser generates 1.3 nJ pulses with parabolic shapes and linear chirps, which can be dechirped to 37 fs. Comb-like dispersion-decreasing fiber should enable the generation of high-energy few-cycle pulses directly from a fiber oscillator. PMID:27176985

  6. Stabilization of a self-referenced, prism-based, Cr:forsterite laser frequency comb using an intracavity prism

    SciTech Connect

    Tillman, Karl A.; Thapa, Rajesh; Knabe, Kevin; Wu Shun; Lim, Jinkang; Washburn, Brian R.; Corwin, Kristan L.

    2009-12-20

    The frequency comb from a prism-based Cr:forsterite laser has been frequency stabilized using intracavity prism insertion and pump power modulation. Absolute frequency measurements of a CW fiber laser stabilized to the P(13) transition of acetylene demonstrate a fractional instability of {approx}2x10{sup -11} at a 1 s gate time, limited by a commercial Global Positioning System (GPS)-disciplined rubidium oscillator. Additionally, absolute frequency measurements made simultaneously using a second frequency comb indicate relative instabilities of 3x10{sup -12} for both combs for a 1 s gate time. Estimations of the carrier-envelope offset frequency linewidth based on relative intensity noise and the response dynamics of the carrier-envelope offset to pump power changes confirm the observed linewidths.

  7. A laser frequency comb that enables radial velocity measurements with a precision of 1 cm s(-1).

    PubMed

    Li, Chih-Hao; Benedick, Andrew J; Fendel, Peter; Glenday, Alexander G; Kärtner, Franz X; Phillips, David F; Sasselov, Dimitar; Szentgyorgyi, Andrew; Walsworth, Ronald L

    2008-04-01

    Searches for extrasolar planets using the periodic Doppler shift of stellar spectral lines have recently achieved a precision of 60 cm s(-1) (ref. 1), which is sufficient to find a 5-Earth-mass planet in a Mercury-like orbit around a Sun-like star. To find a 1-Earth-mass planet in an Earth-like orbit, a precision of approximately 5 cm s(-1) is necessary. The combination of a laser frequency comb with a Fabry-Pérot filtering cavity has been suggested as a promising approach to achieve such Doppler shift resolution via improved spectrograph wavelength calibration, with recent encouraging results. Here we report the fabrication of such a filtered laser comb with up to 40-GHz (approximately 1-A) line spacing, generated from a 1-GHz repetition-rate source, without compromising long-term stability, reproducibility or spectral resolution. This wide-line-spacing comb, or 'astro-comb', is well matched to the resolving power of high-resolution astrophysical spectrographs. The astro-comb should allow a precision as high as 1 cm s(-1) in astronomical radial velocity measurements. PMID:18385734

  8. Echelle spectrograph calibration with a frequency comb based on a harmonically mode-locked fiber laser: a proposal.

    PubMed

    McFerran, J J

    2009-05-10

    Details for constructing an astronomical frequency comb suitable as a wavelength reference for échelle spectrographs associated with optical telescopes are outlined. The source laser for the frequency comb is a harmonically mode-locked fiber laser with a central wavelength of 1.56 microm. The means of producing a repetition rate greater than 7 GHz and a peak optical power of approximately 8 kW are discussed. Conversion of the oscillator light into the visible can occur through a two-step process of (i) nonlinear conversion in periodically poled lithium niobate and (ii) spectral broadening in photonic crystal fiber. While not necessarily octave spanning in spectral range to permit the use of an f -to- 2f interferometer for offset frequency control, the frequency comb can be granted accuracy by linking the mode spacing and a comb tooth to separate frequency references. The design avoids the use of a Fabry-Perot cavity to increase the mode spacing of the frequency comb; however, the level of supermode suppression and sideband asymmetry in the fiber oscillator and in the subsequent frequency conversion stages are aspects that need to be experimentally tested. PMID:19424399

  9. Echelle spectrograph calibration with a frequency comb based on a harmonically mode-locked fiber laser: a proposal

    SciTech Connect

    McFerran, J. J.

    2009-05-10

    Details for constructing an astronomical frequency comb suitable as a wavelength reference for echelle spectrographs associated with optical telescopes are outlined. The source laser for the frequency comb is a harmonically mode-locked fiber laser with a central wavelength of 1.56 {mu}m. The means of producing a repetition rate greater than 7 GHz and a peak optical power of {approx}8 kW are discussed. Conversion of the oscillator light into the visible can occur through a two-step process of (i) nonlinear conversion in periodically poled lithium niobate and (ii) spectral broadening in photonic crystal fiber. While not necessarily octave spanning in spectral range to permit the use of an f -to- 2f interferometer for offset frequency control, the frequency comb can be granted accuracy by linking the mode spacing and a comb tooth to separate frequency references. The design avoids the use of a Fabry-Perot cavity to increase the mode spacing of the frequency comb; however, the level of supermode suppression and sideband asymmetry in the fiber oscillator and in the subsequent frequency conversion stages are aspects that need to be experimentally tested.

  10. Demonstration of a near-IR line-referenced electro-optical laser frequency comb for precision radial velocity measurements in astronomy

    NASA Astrophysics Data System (ADS)

    Yi, X.; Vahala, K.; Li, J.; Diddams, S.; Ycas, G.; Plavchan, P.; Leifer, S.; Sandhu, J.; Vasisht, G.; Chen, P.; Gao, P.; Gagne, J.; Furlan, E.; Bottom, M.; Martin, E. C.; Fitzgerald, M. P.; Doppmann, G.; Beichman, C.

    2016-01-01

    An important technique for discovering and characterizing planets beyond our solar system relies upon measurement of weak Doppler shifts in the spectra of host stars induced by the influence of orbiting planets. A recent advance has been the introduction of optical frequency combs as frequency references. Frequency combs produce a series of equally spaced reference frequencies and they offer extreme accuracy and spectral grasp that can potentially revolutionize exoplanet detection. Here we demonstrate a laser frequency comb using an alternate comb generation method based on electro-optical modulation, with the comb centre wavelength stabilized to a molecular or atomic reference. In contrast to mode-locked combs, the line spacing is readily resolvable using typical astronomical grating spectrographs. Built using commercial off-the-shelf components, the instrument is relatively simple and reliable. Proof of concept experiments operated at near-infrared wavelengths were carried out at the NASA Infrared Telescope Facility and the Keck-II telescope.

  11. Demonstration of a near-IR line-referenced electro-optical laser frequency comb for precision radial velocity measurements in astronomy.

    PubMed

    Yi, X; Vahala, K; Li, J; Diddams, S; Ycas, G; Plavchan, P; Leifer, S; Sandhu, J; Vasisht, G; Chen, P; Gao, P; Gagne, J; Furlan, E; Bottom, M; Martin, E C; Fitzgerald, M P; Doppmann, G; Beichman, C

    2016-01-01

    An important technique for discovering and characterizing planets beyond our solar system relies upon measurement of weak Doppler shifts in the spectra of host stars induced by the influence of orbiting planets. A recent advance has been the introduction of optical frequency combs as frequency references. Frequency combs produce a series of equally spaced reference frequencies and they offer extreme accuracy and spectral grasp that can potentially revolutionize exoplanet detection. Here we demonstrate a laser frequency comb using an alternate comb generation method based on electro-optical modulation, with the comb centre wavelength stabilized to a molecular or atomic reference. In contrast to mode-locked combs, the line spacing is readily resolvable using typical astronomical grating spectrographs. Built using commercial off-the-shelf components, the instrument is relatively simple and reliable. Proof of concept experiments operated at near-infrared wavelengths were carried out at the NASA Infrared Telescope Facility and the Keck-II telescope. PMID:26813804

  12. Demonstration of a near-IR line-referenced electro-optical laser frequency comb for precision radial velocity measurements in astronomy

    PubMed Central

    Yi, X.; Vahala, K.; Li, J.; Diddams, S.; Ycas, G.; Plavchan, P.; Leifer, S.; Sandhu, J.; Vasisht, G.; Chen, P.; Gao, P.; Gagne, J.; Furlan, E.; Bottom, M.; Martin, E. C.; Fitzgerald, M. P.; Doppmann, G.; Beichman, C.

    2016-01-01

    An important technique for discovering and characterizing planets beyond our solar system relies upon measurement of weak Doppler shifts in the spectra of host stars induced by the influence of orbiting planets. A recent advance has been the introduction of optical frequency combs as frequency references. Frequency combs produce a series of equally spaced reference frequencies and they offer extreme accuracy and spectral grasp that can potentially revolutionize exoplanet detection. Here we demonstrate a laser frequency comb using an alternate comb generation method based on electro-optical modulation, with the comb centre wavelength stabilized to a molecular or atomic reference. In contrast to mode-locked combs, the line spacing is readily resolvable using typical astronomical grating spectrographs. Built using commercial off-the-shelf components, the instrument is relatively simple and reliable. Proof of concept experiments operated at near-infrared wavelengths were carried out at the NASA Infrared Telescope Facility and the Keck-II telescope. PMID:26813804

  13. Method for independent and continuous tuning of N lasers phase-locked to the same frequency comb

    NASA Astrophysics Data System (ADS)

    Gunton, Will; Semczuk, Mariusz; Madison, Kirk W.

    2015-09-01

    We present a method of phase-locking any number of continuous-wave lasers to an optical frequency comb (OFC) that enables independent frequency positioning and control of each laser while still maintaining lock to the OFC. The scheme employs an acousto-optic modulator (AOM) in a double pass configuration added to each laser before its light is compared by optical heterodyne with the comb. The only requirement is that the tuning bandwidth of the double pass AOM setup be larger than half the OFC repetition rate. We demonstrate this scheme and achieve an arbitrary frequency tuning precision, a tuning rate of 200~MHz/s and a readout precision at the 1~kHz level.

  14. Retinal, anterior segment and full eye imaging using ultrahigh speed swept source OCT with vertical-cavity surface emitting lasers

    PubMed Central

    Grulkowski, Ireneusz; Liu, Jonathan J.; Potsaid, Benjamin; Jayaraman, Vijaysekhar; Lu, Chen D.; Jiang, James; Cable, Alex E.; Duker, Jay S.; Fujimoto, James G.

    2012-01-01

    We demonstrate swept source OCT utilizing vertical-cavity surface emitting laser (VCSEL) technology for in vivo high speed retinal, anterior segment and full eye imaging. The MEMS tunable VCSEL enables long coherence length, adjustable spectral sweep range and adjustable high sweeping rate (50–580 kHz axial scan rate). These features enable integration of multiple ophthalmic applications into one instrument. The operating modes of the device include: ultrahigh speed, high resolution retinal imaging (up to 580 kHz); high speed, long depth range anterior segment imaging (100 kHz) and ultralong range full eye imaging (50 kHz). High speed imaging enables wide-field retinal scanning, while increased light penetration at 1060 nm enables visualization of choroidal vasculature. Comprehensive volumetric data sets of the anterior segment from the cornea to posterior crystalline lens surface are also shown. The adjustable VCSEL sweep range and rate make it possible to achieve an extremely long imaging depth range of ~50 mm, and to demonstrate the first in vivo 3D OCT imaging spanning the entire eye for non-contact measurement of intraocular distances including axial eye length. Swept source OCT with VCSEL technology may be attractive for next generation integrated ophthalmic OCT instruments. PMID:23162712

  15. Phase-sensitive optical coherence tomography using an Vernier-tuned distributed Bragg reflector swept laser in the mouse middle ear.

    PubMed

    Park, Jesung; Carbajal, Esteban F; Chen, Xi; Oghalai, John S; Applegate, Brian E

    2014-11-01

    Phase-sensitive optical coherence tomography (PhOCT) offers exquisite sensitivity to mechanical vibration in biological tissues. There is growing interest in using PhOCT for imaging the nanometer scale vibrations of the ear in animal models of hearing disorders. Swept-source-based systems offer fast acquisition speeds, suppression of common mode noise via balanced detection, and good signal roll-off. However, achieving high phase stability is difficult due to nonlinear laser sweeps and trigger jitter in a typical swept laser source. Here, we report on the initial application of a Vernier-tuned distributed Bragg reflector (VT-DBR) swept laser as the source for a fiber-based PhOCT system. The VT-DBR swept laser is electronically tuned and precisely controls sweeps without mechanical movement, resulting in highly linear sweeps with high wavelength stability and repeatability. We experimentally measured a phase sensitivity of 0.4 pm standard deviation, within a factor of less than 2 of the computed shot-noise limit. We further demonstrated the system by making ex vivo measurements of the vibrations of the mouse middle ear structures. PMID:25361322

  16. Analysis of the feed-forward method for the referencing of a CW laser to a frequency comb.

    PubMed

    Gatti, D; Sala, T; Gambetta, A; Coluccelli, N; Conti, G Nunzi; Galzerano, G; Laporta, P; Marangoni, M

    2012-10-22

    We report on a comprehensive theoretical and experimental analysis of the feed-forward method for external frequency stabilization of a continuous wave laser against a frequency comb. Application of the method to a distributed feedback diode laser at 1.55 μm allows line narrowing from 800 to 10 kHz, with frequency noise reduction by more than 2 decades up to a Fourier frequency of 100 kHz and a maximum control bandwidth of 0.8 MHz. The results are consistent with a relative phase fluctuation of 1.4 rad rms, as limited by uncompensated high-frequency noise of the slave laser. PMID:23187255

  17. Very high sensor-density multiplexing using a wavelength-to-time domain reflectometry approach based on a rapidly swept akinetic laser

    NASA Astrophysics Data System (ADS)

    Minneman, M. P.; Hoover, E.; Boschert, P.; Ensher, J.; Crawford, M.; Derrickson, D.; Kersey, A. D.

    2015-09-01

    We demonstrate a scheme for the interrogation of arrays of FBG sensors based on a Swept Laser Distributed Sensing system which can achieve 1000 sensors or more in a single fiber, while retaining the sensitivity and repeatability expected with FBG sensors of better than 0.5 μepsilon and 0.05 C. The system utilizes an `akinetic' wavelength swept source and an arrival time-dependent detection approach to allow potentially 1000s of very low reflectivity FBGs to be monitored via a form of Wavelength-to-Time Domain Reflectometry. We demonstrate the interrogation of 250 gratings in a system architecture designed to support 1000 gratings.

  18. All-fiber wavelength swept ring laser based on Fabry-Perot filter for optical frequency domain imaging

    PubMed Central

    Jun, Changsu; Villiger, Martin; Oh, Wang-Yuhl; Bouma, Brett E.

    2014-01-01

    Innovations in laser engineering have yielded several novel configurations for high repetition rate, broad sweep range, and long coherence length wavelength swept lasers. Although these lasers have enabled high performance frequency-domain optical coherence tomography, they are typically complicated and costly and many require access to proprietary materials or devices. Here, we demonstrate a simplified ring resonator configuration that is straightforward to construct from readily available materials at a low total cost. It was enabled by an insight regarding the significance of isolation against bidirectional operation and by configuring the sweep range of the intracavity filter to exceed its free spectral range. The design can easily be optimized to meet a range of operating specifications while yielding robust and stable performance. As an example, we demonstrate 240 kHz operation with 125 nm sweep range and >70 mW of average output power and demonstrate high quality frequency domain OCT imaging. The complete component list and directions for assembly of the laser are posted on-line at www.octresearch.org. PMID:25401614

  19. Laser skin friction measurements and CFD comparison of weak-to-strong swept shock/boundary-layer interactions

    NASA Technical Reports Server (NTRS)

    Kim, K.-S.; Lee, Y.; Alvi, F. S.; Settles, G. S.; Horstman, C. C.

    1990-01-01

    A joint experimental and computational study of skin friction in weak-to-strong swept shock wave/turbulent boundary-layer interactions has been carried out. A planar shock wave is generated by a sharp fin at angles of attack alpha = 10 deg and 16 deg at M(infinity) = 3 and 16 and 20 deg at M(infinity) = 4. Measurements are made using the Laser Interferometer Skin Friction meter, which optically detects the rate of thinning of an oil film applied to the test surface. The results show a systematic rise in the peak c(f) at the rear part of the interaction, where the separated flow atttaches. For the stronget case studied, this peak is an order of magnitude higher than the incoming freestream c(f)level.

  20. Frequency-comb-assisted precision laser spectroscopy of CHF{sub 3} around 8.6 μm

    SciTech Connect

    Gambetta, Alessio; Coluccelli, Nicola; Cassinerio, Marco; Fernandez, Toney Teddy; Gatti, Davide; Laporta, Paolo; Galzerano, Gianluca; Castrillo, Antonio; Fasci, Eugenio; Gianfrani, Livio; Ceausu-Velcescu, Adina; Santamaria, Luigi; Di Sarno, Valentina; Maddaloni, Pasquale; De Natale, Paolo

    2015-12-21

    We report a high-precision spectroscopic study of room-temperature trifluoromethane around 8.6 μm, using a CW quantum cascade laser phase-locked to a mid-infrared optical frequency comb. This latter is generated by a nonlinear down-conversion process starting from a dual-branch Er:fiber laser and is stabilized against a GPS-disciplined rubidium clock. By tuning the comb repetition frequency, several transitions falling in the υ{sub 5} vibrational band are recorded with a frequency resolution of 20 kHz. Due to the very dense spectra, a special multiple-line fitting code, involving a Voigt profile, is developed for data analysis. The combination of the adopted experimental approach and survey procedure leads to fractional accuracy levels in the determination of line center frequencies, down to 2 × 10{sup −10}. Line intensity factors, pressure broadening, and shifting parameters are also provided.

  1. Frequency-comb-assisted precision laser spectroscopy of CHF3 around 8.6 μm.

    PubMed

    Gambetta, Alessio; Coluccelli, Nicola; Cassinerio, Marco; Fernandez, Toney Teddy; Gatti, Davide; Castrillo, Antonio; Ceausu-Velcescu, Adina; Fasci, Eugenio; Gianfrani, Livio; Santamaria, Luigi; Di Sarno, Valentina; Maddaloni, Pasquale; De Natale, Paolo; Laporta, Paolo; Galzerano, Gianluca

    2015-12-21

    We report a high-precision spectroscopic study of room-temperature trifluoromethane around 8.6 μm, using a CW quantum cascade laser phase-locked to a mid-infrared optical frequency comb. This latter is generated by a nonlinear down-conversion process starting from a dual-branch Er:fiber laser and is stabilized against a GPS-disciplined rubidium clock. By tuning the comb repetition frequency, several transitions falling in the υ5 vibrational band are recorded with a frequency resolution of 20 kHz. Due to the very dense spectra, a special multiple-line fitting code, involving a Voigt profile, is developed for data analysis. The combination of the adopted experimental approach and survey procedure leads to fractional accuracy levels in the determination of line center frequencies, down to 2 × 10(-10). Line intensity factors, pressure broadening, and shifting parameters are also provided. PMID:26696053

  2. Frequency Stabilization of High-Power 3.3 μm CW Laser with a Frequency Comb System

    NASA Astrophysics Data System (ADS)

    Kuma, Susumu; Momose, Takamasa

    2010-06-01

    %TEXT OF YOUR ABSTRACT The development of optical frequency combs has enabled a broad range of lasers to be stabilized. In this study, we have developed a system to stabilize high-power CW mid-infrared (MIR) radiation at 3.3 μm using a NIR-VIS frequency comb. The mid-infrared radiation at 3.3 μm were generated as an idler of a CW OPO laser pumped by a 1.064 μm fibre laser. To stabilize the MIR radiation with a frequency comb system in 450 nm to 1.25 μm range, the pump frequency at 1.064 μm and the sum frequency of the MIR radiation and the pump radiation were locked simultaneously to the comb laser. The sum frequency of the MIR and pump radiations was generated in a PPLN crystal. With this technique, we have successfully obtained a width of better than 50 kHz at 3.3 μm with a power of more than 1 W. The stability is currently limited by the response of the PZT in an OPO cavity. Further improvement is underway. The stabilized MIR radiation at 3.3 μm can be used as a source for ultra-high-resolution spectroscopy of vibration-rotation transitions of molecules. Especially, it may be used to decrease the frequency uncertainty of the ν_3 F_2(2) component of the P(7) transition of CH_4, which is one of the optical frequency standards recommended by CIPM. Another application of frequency stabilized MIR radiation is to build-up MIR radiation in a cavity for optical manipulation and trapping of cold molecules we have proposed in New. J. Phys. 11. 055023 (2009).

  3. Optical frequency comb generator based on a monolithically integrated passive mode-locked ring laser with a Mach-Zehnder interferometer.

    PubMed

    Corral, V; Guzmán, R; Gordón, C; Leijtens, X J M; Carpintero, G

    2016-05-01

    We report the demonstration of an optical-frequency comb generator based on a monolithically integrated ring laser fabricated in a multiproject wafer run in an active/passive integration process in a generic foundry using standardized building blocks. The device is based on a passive mode-locked ring laser architecture, which includes a Mach-Zehnder interferometer to flatten the spectral shape of the comb output. This structure allows monolithic integration with other optical components, such as optical filters for wavelength selection, or dual wavelength lasers for their stabilization. The results show a -10  dB span of the optical comb of 8.7 nm (1.08 THz), with comb spacing of 10.16 GHz. We also obtain a flatness of 44 lines within a 1.8 dB power variation. PMID:27128043

  4. Fiber-laser frequency combs for the generation of tunable single-frequency laser lines, mm- and THz-waves and sinc-shaped Nyquist pulses

    NASA Astrophysics Data System (ADS)

    Schneider, Thomas

    2015-03-01

    High-quality frequency comb sources like femtosecond-lasers have revolutionized the metrology of fundamental physical constants. The generated comb consists of frequency lines with an equidistant separation over a bandwidth of several THz. This bandwidth can be broadened further to a super-continuum of more than an octave through propagation in nonlinear media. The frequency separation between the lines is defined by the repetition rate and the width of each comb line can be below 1 Hz, even without external stabilization. By extracting just one of these lines, an ultra-narrow linewidth, tunable laser line for applications in communications and spectroscopy can be generated. If two lines are extracted, the superposition of these lines in an appropriate photo-mixer produces high-quality millimeter- and THz-waves. The extraction of several lines can be used for the creation of almost-ideally sinc-shaped Nyquist pulses, which enable optical communications with the maximum-possible baud rate. Especially combs generated by low-cost, small-footprint fs-fiber lasers are very promising. However due to the resonator length, the comb frequencies have a typical separation of 80 - 100 MHz, far too narrow for the selection of single tones with standard optical filters. Here the extraction of single lines of an fs-fiber laser by polarization pulling assisted stimulated Brillouin scattering is presented. The application of these extracted lines as ultra-narrow, stable and tunable laser lines, for the generation of very high-quality mm and THz-waves with an ultra-narrow linewidth and phase noise and for the generation of sinc-shaped Nyquist pulses with arbitrary bandwidth and repetition rate is discussed.

  5. Optical frequency domain imaging with a rapidly swept laser in the 1300nm bio-imaging window

    NASA Astrophysics Data System (ADS)

    Meleppat, Ratheesh Kumar; Vadakke Matham, Murukeshan; Seah, Leong Keey

    2015-07-01

    Optical frequency domain imaging system (OFDI) in the 1300nm biological imaging window is demonstrated by using a high speed frequency swept laser source. The output of the laser with central wave length of 1320nm is continuously tuned over a bandwidth of 100nm with a repetition rate of 16 KHz. The laser source has an instantaneous coherence length of 6mm and delivers an average power of 12mW. Axial resolution ~ 6μm in the biological tissue and peak sensitivity of 110dB are achieved. The experimentally determined values of the imaging parameters such as the axial resolution, sensitivity and depth range are found to be in good agreement with the theoretically estimated values. The developed system is capable of generating the images of size 512x1024 at a rate of 20 frames per second. High resolution and high contrast images of the finger nail and anterior chamber of a pig's eye acquired using the developed OFDI system are presented, which demonstrate the feasibility of the system for in-vivo biomedical imaging applications.

  6. Line profile analysis of an astronomical spectrograph with a laser frequency comb

    NASA Astrophysics Data System (ADS)

    Zhao, Fei; Zhao, Gang; Lo Curto, Gaspare; Wang, Hui-Juan; Liu, Yu-Juan; Wang, Liang; Wang, Wei

    2014-08-01

    We present a study of the spectral line shape associated with a High Resolution Spectrograph on the 2.16 m telescope at the Xinglong Observing Station of National Astronomical Observatories, Chinese Academy of Sciences. This measurement is based on modeling the instrumental line shape obtained by unresolved modes from a Yb-fiber mode-locked laser frequency comb. With the current repetition rate of 250 MHz and 26 GHz mode spacing on the spectrograph, we find the absolute variation of the line center, 0.0597 pixel in the direction of the CCDs, and 0.00275 pixel (~3 m s-1) for relative variation in successive exposures on a short timescale. A novel double-Gaussian model is presented to improve the quality of the fit by a factor of 2.47 in a typical single exposure. We also use analysis with raw moments and central moments to characterize the change in line shape across the detector. A trend in charge transfer efficiency can be found on the E2V 4096 × 4096 CCD that provides a correction for wavelength calibration aiming to reach a level of precision for radial velocity below 1 ms-1.

  7. Wide tuning range wavelength-swept laser with a single SOA at 1020 nm for ultrahigh resolution Fourier-domain optical coherence tomography.

    PubMed

    Lee, Sang-Won; Song, Hyun-Woo; Jung, Moon-Youn; Kim, Seung-Hwan

    2011-10-24

    In this study, we demonstrated a wide tuning range wavelength-swept laser with a single semiconductor optical amplifier (SOA) at 1020 nm for ultrahigh resolution, Fourier-domain optical coherence tomography (UHR, FD-OCT). The wavelength-swept laser was constructed with an external line-cavity based on a Littman configuration. An optical wavelength selection filter consisted of a grating, a telescope, and a polygon scanner. Before constructing the optical wavelength selection filter, we observed that the optical power, the spectrum bandwidth, and the center wavelength of the SOA were affected by the temperature of the thermoelectric (TE) cooler in the SOA mount as well as the applied current. Therefore, to obtain a wide wavelength tuning range, we adjusted the temperature of the TE cooler in the SOA mount. When the temperature in the TE cooler was 9 °C, our swept source had a tuning range of 142 nm and a full-width at half-maximum (FWHM) of 121.5 nm at 18 kHz. The measured instantaneous spectral bandwidth (δλ) is 0.085 nm, which was measured by an optical spectrum analyzer with a resolution bandwidth of 0.06 nm. This value corresponds to an imaging depth of 3.1 mm in air. Additionally, the averaged optical power of our swept source was 8.2 mW. In UHR, FD/SS-OCT using our swept laser, the measured axial resolution was 4.0 μm in air corresponding to 2.9 μm in tissue (n = 1.35). The sensitivity was measured to be 93.1 dB at a depth of 100 μm. Finally, we obtained retinal images (macular and optic disk) and a corneal image. PMID:22108975

  8. Selection and amplification of a single optical frequency comb mode for laser cooling of the strontium atoms in an optical clock

    SciTech Connect

    Liu, Hui; Yin, Mojuan; Kong, Dehuan; Xu, Qinfang; Zhang, Shougang; Chang, Hong

    2015-10-12

    In this paper, we report on the active filtering and amplification of a single mode from an optical femtosecond laser comb with mode spacing of 250 MHz by optical injection of two external-cavity diode lasers operating in cascade to build a narrow linewidth laser for laser cooling of the strontium atoms in an optical lattice clock. Despite the low injection of individual comb mode of approximately 50 nW, a single comb line at 689 nm could be filtered and amplified to reach as high as 10 mW with 37 dB side mode suppression and a linewidth of 240 Hz. This method could be applied over a broad spectral band to build narrow linewidth lasers for various applications.

  9. Combining laser frequency combs and iodine cell calibration techniques for Doppler detection of exoplanets

    NASA Astrophysics Data System (ADS)

    Cahoy, Kerri; Fischer, Debra; Spronck, Julien; DeMille, David

    2010-07-01

    Exoplanets can be detected from a time series of stellar spectra by looking for small, periodic shifts in the absorption features that are consistent with Doppler shifts caused by the presence of an exoplanet, or multiple exoplanets, in the system. While hundreds of large exoplanets have already been discovered with the Doppler technique (also called radial velocity), our goal is to improve the measurement precision so that many Earth-like planets can be detected. The smaller mass and longer period of true Earth analogues require the ability to detect a reflex velocity of ~10 cm/s over long time periods. Currently, typical astronomical spectrographs calibrate using either Iodine absorptive cells or Thorium Argon lamps and achieve ~10 m/s precision, with the most stable spectrographs pushing down to ~2 m/s. High velocity precision is currently achieved at HARPS by controlling the thermal and pressure environment of the spectrograph. These environmental controls increase the cost of the spectrograph, and it is not feasible to simply retrofit existing spectrometers. We propose a fiber-fed high precision spectrograph design that combines the existing ~5000-6000 A Iodine calibration system with a high-precision Laser Frequency Comb (LFC) system from ~6000-7000 A that just meets the redward side of the Iodine lines. The scientific motivation for such a system includes: a 1000 A span in the red is currently achievable with LFC systems, combining the two calibration methods increases the wavelength range by a factor of two, and moving redward decreases the "noise" from starspots. The proposed LFC system design employs a fiber laser, tunable serial Fabry-Perot cavity filters to match the resolution of the LFC system to that of standard astronomical spectrographs, and terminal ultrasonic vibration of the multimode fiber for a stable point spread function.

  10. Generation of Kerr combs centered at 4.5 μm in crystalline microresonators pumped with quantum-cascade lasers.

    PubMed

    Savchenkov, Anatoliy A; Ilchenko, Vladimir S; Di Teodoro, Fabio; Belden, Paul M; Lotshaw, William T; Matsko, Andrey B; Maleki, Lute

    2015-08-01

    We report on the generation of mid-infrared Kerr frequency combs in high-finesse CaF2 and MgF2 whispering-gallery-mode resonators pumped with continuous-wave room-temperature quantum cascade lasers. The combs were centered at 4.5 μm, the longest wavelength to date. A frequency comb wider than one half of an octave was demonstrated when approximately 20 mW of pump power was coupled to an MgF2 resonator characterized with quality factor exceeding 10(8). PMID:26258334

  11. Traceable dual-frequency measurement of Zeeman split He-Ne lasers using an optical frequency comb locked external cavity diode laser

    NASA Astrophysics Data System (ADS)

    Wei, Haoyun; Wu, Xuejian; Zhou, Lei; Zhang, Jitao; Li, Yan

    2012-11-01

    A frequency measurement system for dual frequency He-Ne lasers is set up based on an external cavity diode laser locked to fiber femtosecond optical frequency comb using an Rb clock as a frequency standard. The frequencies of the Zeeman split orthogonal polarized lasers are measured by beating with the locked diode laser at the same time. Locking the diode laser to the 1 894 449th comb tooth, the absolute frequency of the diode laser is 473 612 190 000.0 (2.4) kHz, with a relative frequency uncertainty of 5.1×10-12. A commercial dual frequency He-Ne laser is measured to test the system, and the results show that the mean absolute frequencies of the horizontal polarized laser and the vertical polarized laser are 473 612 229 934 kHz and 473 612 232 111 kHz, respectively, with a relative Allan deviation of 5.2× 10-11 at 1 024 s, and the mean split frequency is 2.177 MHz with a standard deviation of 2 kHz.

  12. Implementation of a data processing platform for real-time distance measurement with dual-comb lasers

    NASA Astrophysics Data System (ADS)

    Ni, Kai; Xu, Mingfei; Zhou, Qian; Dong, Hao; Li, Xinghui; Wu, Guanhao

    2015-08-01

    Absolute distance measurement with dual femtosecond comb lasers has advantages of wide-range, high-accuracy and fast speed. It combines time-of-flight and interferometric measurement. The novelty of ranging method leads to new challenges in designing the data acquisition and processing hardware system. Currently there are no available real-time data processing system for dual-comb ranging. This paper introduces our recent progress on designing and implementing such a platform. Our platform mainly contains four different function modules. First, a clock module that accept a 250MHz maximum reference clock input was introduced to generate the sample clock for A/D converter, and the module's output clock can be delayed up to 20ns with a resolution of 714ps. Second, a high-speed data acquisition module with a 14-bit resolution and a 125 MSPS maximum sample rate was designed to convert the analog laser pulse signal to digital signal. Third, we built a real-time data processing module that allows an input of 16-bit data in the FPGA to calculate the distance from the digital signal within 83us. Finally, a data transmission module based on a 128MB DDR SDRAM and USB2.0 was added so that we can easily debug the platform in the PC. The performance of our system is evaluated in real-time. The test bench consists of two femtosecond laser sources, an optical fiber interferometer and our data processing system. The repetition frequencies of the two combs are around 50MHz, with frequency difference of 2.5kHz. The center wavelength of laser pulses is 1560nm. The target distance is from 0m to 3m. The experimental results show that our system can output measurement results at the rate of 2500 pts/s, and the measurement deviation is less than 10um.

  13. Multifunctional tunable multiwavelength erbium-doped fiber laser based on tunable comb filter and intensity-dependent loss modulation

    NASA Astrophysics Data System (ADS)

    Quan, Mingran; Li, Yuan; Tian, Jiajun; Yao, Yong

    2015-04-01

    A multiwavelength erbium-doped fiber laser based on tunable comb spectral filter and intensity-dependent loss modulation is proposed and experimentally demonstrated. The laser allows fine and multifunctional tunable operations of channel-spacing, peak-location, spectral-range, and wavelength-number. More specifically, channel-spacing switch from 0.4 nm to 0.2 nm and peak-location adjustment within half of free spectrum range are obtained via controlling the tunable comb filter. The wavelength-number and the spectral-range of the lasing lines can be accurately controlled by intensity-dependent loss modulation in the laser cavity, enabled by a power-symmetric nonlinear optical loop mirror. In addition, fine control over the wavelength-number at fixed spectral-range is realized by simply adjusting the pump power. More important, the tunable operation process for every type of specific parameter is individual, without influences for other output parameters. Such features of this fiber laser make it useful and convenient for the practical application.

  14. Defense of fake fingerprint attacks using a swept source laser optical coherence tomography setup

    NASA Astrophysics Data System (ADS)

    Meissner, Sven; Breithaupt, Ralph; Koch, Edmund

    2013-03-01

    The most established technique for the identification at biometric access control systems is the human fingerprint. While every human fingerprint is unique, fingerprints can be faked very easily by using thin layer fakes. Because commercial fingerprint scanners use only a two-dimensional image acquisition of the finger surface, they can only hardly differentiate between real fingerprints and fingerprint fakes applied on thin layer materials. A Swept Source OCT system with an A-line rate of 20 kHz and a lateral and axial resolution of approximately 13 μm, a centre wavelength of 1320 nm and a band width of 120 nm (FWHM) was used to acquire fingerprints and finger tips with overlying fakes. Three-dimensional volume stacks with dimensions of 4.5 mm x 4 mm x 2 mm were acquired. The layering arrangement of the imaged finger tips and faked finger tips was analyzed and subsequently classified into real and faked fingerprints. Additionally, sweat gland ducts were detected and consulted for the classification. The manual classification between real fingerprints and faked fingerprints results in almost 100 % correctness. The outer as well as the internal fingerprint can be recognized in all real human fingers, whereby this was not possible in the image stacks of the faked fingerprints. Furthermore, in all image stacks of real human fingers the sweat gland ducts were detected. The number of sweat gland ducts differs between the test persons. The typical helix shape of the ducts was observed. In contrast, in images of faked fingerprints we observe abnormal layer arrangements and no sweat gland ducts connecting the papillae of the outer fingerprint and the internal fingerprint. We demonstrated that OCT is a very useful tool to enhance the performance of biometric control systems concerning attacks by thin layer fingerprint fakes.

  15. Broadband Frequency Comb and Cw-Laser Velocity Modulation Spectroscopy of ThF+

    NASA Astrophysics Data System (ADS)

    Gresh, Dan; Cossel, Kevin; Ye, Jun; Cornell, Eric

    2015-06-01

    An experimental search for the permanent electric dipole moment of the electron (eEDM) is currently being performed using the metastable ^3Δ_1 state in trapped HfF^+ ^(^). The use of ThF^+ could significantly increase the sensitivity due to the larger effective electric field and longer ^3Δ_1 state lifetime. Previous work by the Heaven group has identified several low-lying ThF^+ electronic states; however, the ground state could not be conclusively assigned. In addition, transitions to intermediate electronic states have not been identified, but they are necessary for state detection, manipulation, and readout in an eEDM experiment. To date we have acquired 3700 wn of densely-sampled ThF^+ spectra in the 695 - 1020 nm region with frequency comb and cw-laser velocity modulation spectroscopy. With high resolution, we have accurately fit more than 20 ThF^+ vibronic transitions, including electronic states spaced by the known X-a energy separation^b. We will report on the ThF^+ ground state assignment and its implications for an eEDM experiment. H. Loh, K. C. Cossel, M. C. Grau, K.-K. Ni, E. R. Meyer, J. L. Bohn, J. Ye, E. A. Cornell, Science 342, 1220 (2013). B. J. Barker, I. O. Antonov, M. C. Heaven, K. A. Peterson, J. Chem. Phys. 136, 104305 (2012). L. C. Sinclair, K. C. Cossel, T. Coffey, J. Ye, E. A. Cornell, PRL 107, 093002 (2011). K.C. Cossel et. al., Chem. Phys. Lett. 546, 1 (2012).

  16. Rapid Swept-Wavelength External Cavity Quantum Cascade Laser for Open Path Sensing

    SciTech Connect

    Brumfield, Brian E.; Phillips, Mark C.

    2015-07-01

    A rapidly tunable external cavity quantum cascade laser system is used for open path sensing. The system permits acquisition of transient absorption spectra over a 125 cm-1 tuning range in less than 0.01 s.

  17. Low-threshold collinear parametric Raman comb generation in calcite under 532 and 1064 nm picosecond laser pumping

    NASA Astrophysics Data System (ADS)

    Smetanin, S. N.; Jelínek, M., Jr.; Kubeček, V.; Jelínková, H.

    2015-09-01

    Optimal conditions of low-threshold collinear parametric Raman comb generation in calcite (CaCO3) are experimentally investigated under 20 ps laser pulse excitation, in agreement with the theoretical study. The collinear parametric Raman generation of the highest number of Raman components in the short calcite crystals corresponding to the optimal condition of Stokes-anti-Stokes coupling was achieved. At the excitation wavelength of 1064 nm, using the optimum-length crystal resulted in the effective multi-octave frequency Raman comb generation containing up to five anti-Stokes and more than four Stokes components (from 674 nm to 1978 nm). The 532 nm pumping resulted in the frequency Raman comb generation from the 477 nm 2nd anti-Stokes up to the 692 nm 4th Stokes component. Using the crystal with a non-optimal length leads to the Stokes components generation only with higher thresholds because of the cascade-like stimulated Raman scattering with suppressed parametric coupling.

  18. Optical Frequency Metrology of an Iodine-Stabilized He-Ne Laser Using the Frequency Comb of a Quantum-Interference-Stabilized Mode-Locked Laser

    PubMed Central

    Smith, Ryan P.; Roos, Peter A.; Wahlstrand, Jared K.; Pipis, Jessica A.; Rivas, Maria Belmonte; Cundiff, Steven T.

    2007-01-01

    We perform optical frequency metrology of an iodine-stabilized He-Ne laser using a mode-locked Ti:sapphire laser frequency comb that is stabilized using quantum interference of photocurrents in a semiconductor. Using this technique, we demonstrate carrier-envelope offset frequency fluctuations of less than 5 mHz using a 1 s gate time. With the resulting stable frequency comb, we measure the optical frequency of the iodine transition [127I2 R(127) 11-5 i component] to be 473 612 214 712.96 ± 0.66 kHz, well within the uncertainty of the CIPM recommended value. The stability of the quantum interference technique is high enough such that it does not limit the measurements. PMID:27110472

  19. Linear FBG interrogation with a wavelength-swept fiber laser and a volume phase grating spectrometer

    NASA Astrophysics Data System (ADS)

    Kim, Hyunjin; Song, Minho

    2011-05-01

    We propose a novel FBG (fiber Bragg grating) sensor system that uses a tunable wavelength laser and a volume phase grating spectrometer. The effect of nonlinear wavelength scanning and uneven power profile of the fiber laser, which substantially degrades the measurement accuracy, is minimized by using a spectrometer demodulation. The constructed sensor system showed linear output according to the Bragg wavelength variation, and showed much higher signal-to-noise ratio compared to the conventional spectrometer demodulation which used much dimmer broadband light sources.

  20. A frequency-stabilized Yb:KYW femtosecond laser frequency comb and its application to low-phase-noise microwave generation

    NASA Astrophysics Data System (ADS)

    Meyer, Stephanie A.; Fortier, Tara M.; Lecomte, Steve; Diddams, Scott A.

    2013-09-01

    We present an optically stabilized Yb:KYW fs-laser frequency comb. We use an f-2 f nonlinear interferometer to measure the carrier envelope offset frequency ( f 0) and the heterodyne beatnote between the comb and a stable CW laser at 1068 nm to detect fluctuations in the comb repetition rate (). Both of these degrees of freedom of the comb are then controlled using phase-locked loops. As a demonstration of the frequency-stabilized comb, we generate low-phase-noise 10 GHz microwaves through detection of the pulse train on a high bandwidth photodiode. The phase noise of the resulting 10 GHz microwaves was -99 dBc/Hz at 1 Hz and the corresponding Allen deviation was <2.6 × 10-15 at 1 s, measured by comparison to an independently stabilized Ti:sapphire frequency comb. This room-temperature, optically based source of microwaves has close-to-carrier phase noise comparable to the very best cryogenic microwave oscillators.

  1. Diode-pumped Yb:KYW femtosecond laser frequency comb with stabilized carrier-envelope offset frequency

    NASA Astrophysics Data System (ADS)

    Meyer, S. A.; Squier, J. A.; Diddams, S. A.

    2008-06-01

    We describe the detection and stabilization of the carrier envelope offset (CEO) frequency of a diode-pumped Yb:KYW (ytterbium-doped potassium yttrium tungstate) femtosecond oscillator that is spectrally centered at 1033 nm. The system consists of a diode-pumped, passively mode-locked femtosecond laser that produces 290 fs pulses at a repetition rate of 160 MHz. These pulses are first amplified, spectrally broadened and temporally compressed to 80 fs, and then launched into microstructured fiber to produce an octave-spanning spectrum. An f-2f nonlinear interferometer is employed with the broadened spectrum to detect and stabilize the CEO frequency through feedback to the pump laser current. These results demonstrate that such a Yb-doped tungstate laser can provide an efficient, compact, high-repetition-rate optical frequency comb with coverage from 650-1450 nm.

  2. Real-Time Determination of Absolute Frequency in Continuous-Wave Terahertz Radiation with a Photocarrier Terahertz Frequency Comb Induced by an Unstabilized Femtosecond Laser

    NASA Astrophysics Data System (ADS)

    Minamikawa, Takeo; Hayashi, Kenta; Mizuguchi, Tatsuya; Hsieh, Yi-Da; Abdelsalam, Dahi Ghareab; Mizutani, Yasuhiro; Yamamoto, Hirotsugu; Iwata, Tetsuo; Yasui, Takeshi

    2016-05-01

    A practical method for the absolute frequency measurement of continuous-wave terahertz (CW-THz) radiation uses a photocarrier terahertz frequency comb (PC-THz comb) because of its ability to realize real-time, precise measurement without the need for cryogenic cooling. However, the requirement for precise stabilization of the repetition frequency ( f rep) and/or use of dual femtosecond lasers hinders its practical use. In this article, based on the fact that an equal interval between PC-THz comb modes is always maintained regardless of the fluctuation in f rep, the PC-THz comb induced by an unstabilized laser was used to determine the absolute frequency f THz of CW-THz radiation. Using an f rep-free-running PC-THz comb, the f THz of the frequency-fixed or frequency-fluctuated active frequency multiplier chain CW-THz source was determined at a measurement rate of 10 Hz with a relative accuracy of 8.2 × 10-13 and a relative precision of 8.8 × 10-12 to a rubidium frequency standard. Furthermore, f THz was correctly determined even when fluctuating over a range of 20 GHz. The proposed method enables the use of any commercial femtosecond laser for the absolute frequency measurement of CW-THz radiation.

  3. Stable multi-wavelength PM-EDF linear cavity laser employing a TCF fiber comb filter and an SNOLM

    NASA Astrophysics Data System (ADS)

    Zou, Hui; Lou, Shuqin; Su, Wei; Wang, Xin; Han, Bolin

    2013-10-01

    We propose and demonstrate a stable multi-wavelength polarization-maintaining erbium-doped fiber (PM-EDF) linear cavity laser by using a twin-core fiber (TCF) comb filter and a symmetric nonlinear optical loop mirror (SNOLM). Using a homemade TCF, we fabricate a TCF comb filter with a channel spacing of 0.29 nm. By adjusting the polarization controllers (PCs) carefully, the polarization hole-burning effect in the PM-EDF is enhanced and intensity-dependent loss is produced by a nonlinear polarization rotation effect in the SNOLM. As a result, the homogeneous broadening gain medium is effectively reduced, and the mode competition of the EDF is distinctly suppressed. With only 100 mW pump power, up to 52-wavelength stable outputs with channel spacing of 0.29 nm have been achieved at room temperature. The power fluctuation and wavelength shift for each lasing wavelength are less than 0.1 dB and 0.02 nm in an hour, respectively. Experimental results illustrate that the proposed structure of a fiber laser can realize multi-wavelength outputs with high stability at lower pump power.

  4. VCSEL Swept Light Sources

    NASA Astrophysics Data System (ADS)

    Jayaraman, Vijaysekhar; Jiang, James; Potsaid, Benjamin; Robertson, Martin; Heim, Peter J. S.; Burgner, Christopher; John, Demis; Cole, Garrett D.; Grulkowski, Ireneusz; Fujimoto, James G.; Davis, Anjul M.; Cable, Alex E.

    Wavelength-swept light sources are widely recognized as a critical enabling technology for swept source optical coherence tomography (SS-OCT). In recent years, amplified micro-electromechanical systems tunable vertical cavity surface-emitting lasers (MEMS-VCSELs) have emerged as a high performance swept source, providing a unique combination of of wide tuning range, high maximum sweep rate, variable sweep rate, long dynamic coherence length enabled by dynamic mode-hop-free single mode operation, high optical power, and excellent imaging quality. Other important parameters provided by these devices include operation in a stable polarization state, low output power ripple, and linearized wavelength sweeping. This work describes MEMS-VCSEL device design, fabrication, and performance for devices in the 1050nm band relevant to ophthalmic imaging, and the 1310nm band relevant to vascular, skin, and anatomic imaging. Tuning ranges achieved include 100 nm at 1050nm and 150nm at 1310, with the latter result representing the widest tuning range of any MEMS-VCSEL at any wavelength. Both 1050 and 1310nm devices have enabled record imaging speed, record imaging range, and enhanced SS-OCT imaging.

  5. Large-bandwidth two-color free-electron laser driven by a comb-like electron beam

    NASA Astrophysics Data System (ADS)

    Ronsivalle, C.; Anania, M. P.; Bacci, A.; Bellaveglia, M.; Chiadroni, E.; Cianchi, A.; Ciocci, F.; Dattoli, G.; Di Giovenale, D.; Di Pirro, G.; Ferrario, M.; Gatti, G.; Giannessi, L.; Mostacci, A.; Musumeci, P.; Palumbo, L.; Petralia, A.; Petrillo, V.; Pompili, R.; Rau, J. V.; Rossi, A. R.; Vaccarezza, C.; Villa, F.

    2014-03-01

    We discuss a two-color SASE free-electron laser (FEL) amplifier where the time and energy separation of two separated radiation pulses are controlled by manipulation of the electron beam phase space. Two electron beamlets with adjustable time and energy spacing are generated in an RF photo-injector illuminating the cathode with a comb-like laser pulse followed by RF compression in the linear accelerator. We review the electron beam manipulation technique to generate bunches with time and energy properties suitable for driving two-color FEL radiation. Experimental measurements at the SPARC-LAB facility illustrate the flexibility of the scheme for the generation of two-color FEL spectra.

  6. Direct comparison of two cold-atom-based optical frequency standards by using a femtosecond-laser comb.

    PubMed

    Vogel, K R; Diddams, S A; Oates, C W; Curtis, E A; Rafac, R J; Itano, W M; Bergquist, J C; Fox, R W; Lee, W D; Wells, J S; Hollberg, L

    2001-01-15

    With a fiber-broadened, femtosecond-laser frequency comb, the 76-THz interval between two laser-cooled optical frequency standards was measured with a statistical uncertainty of 2x10(-13) in 5 s , to our knowledge the best short-term instability thus far reported for an optical frequency measurement. One standard is based on the calcium intercombination line at 657 nm, and the other, on the mercury ion electric-quadrupole transition at 282 nm. By linking this measurement to the known Ca frequency, we report a new frequency value for the Hg(+) clock transition with an improvement in accuracy of ~10(5) compared with its best previous measurement. PMID:18033520

  7. Dimensional metrology using the optical comb of a mode-locked laser

    NASA Astrophysics Data System (ADS)

    Jin, Jonghan

    2016-02-01

    In the field of dimensional metrology, significant technical challenges have been encountered with regard to large-scale object assembly, satellite positioning, control of the long-distance precision stage, and inspections of large steps or deep holes on semiconductor devices and multi-layered display panels. The key elements required are high speeds, a long dynamic measurable range, and good precision of measurements, and conventional methods can scarcely meet such requirements simultaneously. Promisingly, the advent of the optical comb has opened up numerous possibilities to break through practical limits by exploiting several of its unique features. These include inter-mode interference, a wide spectral bandwidth with a long coherence length and well-defined longitudinal modes. In this review, various dimensional metrological methods using the optical comb are introduced, describing their basic principles and applications in scientific as well as industrial areas.

  8. Self referenced Yb-fiber-laser frequency comb using a dispersion micromanaged tapered holey fiber.

    PubMed

    Pal, Parama; Knox, Wayne H; Hartl, Ingmar; Fermann, Martin E

    2007-09-17

    We demonstrate a fully stabilized frequency comb in the 1mum spectral region based on an Yb-fiber oscillator and a cladding pumped chirped pulse Yb-fiber amplifier whose output is spectrally broadened in a dispersion micromanaged holey fiber. The dispersion micromanaged fiber is used to generate efficient, low noise spectral components at 523nm which are heterodyned with the second harmonic of the amplifier output for standard f-to-2f self-referenced carrier envelope offset frequency detection. For comb stabilization we phase-lock this offset frequency and the oscillator repetition frequency simultaneously to an RF reference by feedback controlling the oscillator pump diode current and the driving voltage of an intracavity piezo-electric fiber stretcher respectively. PMID:19547582

  9. Precision absolute frequency laser spectroscopy of argon II in parallel and antiparallel geometry using a frequency comb for calibration

    NASA Astrophysics Data System (ADS)

    Lioubimov, Vladimir

    A collinear fast ion beam laser apparatus was constructed and tested. It will be used on-line to the SLOW RI radioactive beam facility in RIKEN (Japan) and as in the present experiment for precision absolute frequency measurements of astrophysically important reference lines. In the current work we conducted absolute measurements of spectral lines of Ar+ ions using parallel and antiparallel geometries. To provide a reference for the laser wavelength iodine saturation spectroscopy was used. The precision of this reference was enhanced by simultaneously observing the beat node between the spectroscopy laser and the corresponding mode of a femtosecond laser frequency comb. When performing collinear and anticollinear measurements simultaneously for the laser induced fluorescence, the exact relativistic formula for the transition frequency n0=ncoll˙n anticoll can be applied. In this geometry ion source instabilities due to pressure and anode voltage fluctuation are minimized. The procedure of fluorescence lineshapes fitting is discussed and the errors in the measurements are estimated. The result is n0 = 485, 573, 619.7 +/- 0.3MHz corresponding to Dnn = 6 x 10-10 and is an improvement of two orders of magnitude over the NIST published value.

  10. Optical frequency comb generation with a flat-top spectrum from a mode-locked Yb fiber laser

    NASA Astrophysics Data System (ADS)

    Jang, Gwang Hoon; Yoon, Tai Hyun

    2012-02-01

    We present an ultrabroadband supercontinuum (SC) frequency comb generation covering the optical spectrum more than 1.2 octave from 570 nm to 1350 nm with a near flat-top power spectrum by using a mode-locked Yb fiber laser at 1030 nm as a master oscillator (MO). The repetition rate of the MO that has a spectral-width of 28 nm is 152 MHz and is phase-locked to a reference frequency synthesizer. A power amplifier is used to boost up the output power up to 1.3 W and the positively chirped amplified pulses are compressed by using a transmission grating pair. We used a commercially-available 10-cm long photonic crystal fiber that has two zero-dispersion wavelengths at 800 nm and 1093 nm, respectively, to generate an ultrabroadband SC frequency comb. Optical spectrum depending on the frequency chirp and pulse-width of the amplified pulses are analyzed to find an optimum coupling power as well as an optimum chirp parameter. We found that a dimensionless chirp parameter of 8.6 and a pulse-width of 517 fs for a chirped Gaussian pulse resulted in the optimum spectrum width of 1.2 octave.

  11. Fast wavelength-swept dispersion-tuned fiber laser over 500kHz using a wideband chirped fiber Bragg grating

    NASA Astrophysics Data System (ADS)

    Yamashita, Shinji; Takubo, Yuya

    2011-05-01

    We proposed a wide and fast wavelength-swept fiber lasers based on the dispersion tuning for the optical coherence tomography (OCT) applications. So far, we have achieved the sweep rate of ~200kHz at the sweep bandwidth of ~180nm. The sweep rate is only limited by the photon lifetime, which is proportional to the cavity length. Since we used a dispersion compensating fiber (DCF) as the dispersive medium, the long cavity length (~100m) was the limit of the sweep rate. In this paper, we demonstrate faster sweep rate up to ~500kHz by using a wideband chirped fiber Bragg grating (CFBG).

  12. Mid-infrared quantitative spectroscopy by comb-referencing of a quantum-cascade-laser: Application to the CO2 spectrum at 4.3 μm

    NASA Astrophysics Data System (ADS)

    Gambetta, A.; Gatti, D.; Castrillo, A.; Galzerano, G.; Laporta, P.; Gianfrani, L.; Marangoni, M.

    2011-12-01

    A robust phase-lock of a quantum-cascade-laser to a near-infrared frequency-comb allows absorption spectra of a CO2 gas sample to be acquired at different pressures with extreme repeatability and accuracy by tuning the repetition-rate of the comb, thus ensuring an absolute frequency scale on the acquired spectra. The method proves useful to retrieve traceable spectroscopic parameters such as line-center frequencies, line intensity factors, pressure shift, and pressure broadening coefficients, with unprecedented quality from the metrological point of view.

  13. Effects of the Lexington LaserComb on hair regrowth in the C3H/HeJ mouse model of alopecia areata.

    PubMed

    Wikramanayake, Tongyu Cao; Rodriguez, Rosa; Choudhary, Sonal; Mauro, Lucia M; Nouri, Keyvan; Schachner, Lawrence A; Jimenez, Joaquin J

    2012-03-01

    Alopecia areata (AA) is a common autoimmune disease that presents with non-scarring alopecia. It is characterized by intra- or peri-follicular lymphocytic infiltrates composed of CD4+ and CD8+ T-cells on histology. To this day, few treatments are effective for AA. Here we present findings of using a low-level laser comb to alleviate the symptoms of AA in a C3H/HeJ mouse model for AA. Fourteen C3H/HeJ mice with induced AA were used in this study. Two were killed to confirm AA through histology. The remaining 12 mice were randomized into two groups; group I received HairMax LaserComb (wavelength: 655 nm, beam diameter <5 mm; divergence 57 mrad; nine lasers) for 20 s daily, three times per week for a total of 6 weeks; group II was treated similarly, except that the laser was turned off (sham-treated). After 6 weeks of LaserComb treatment, hair regrowth was observed in all the mice in group I (laser-treated) but none in group II (sham-treated). On histology, increased number of anagen hair follicles was observed in laser-treated mice. On the other hand, sham-treated mice demonstrated hair follicles in the telogen phase with no hair shaft. LaserComb seems to be an effective and convenient device for the treatment of AA in the C3H/HeJ mouse model. Human studies are required to determine the efficacy and safety of this device for AA therapy. PMID:21739260

  14. Absolute distance measurement by multi-heterodyne interferometry using a frequency comb and a cavity-stabilized tunable laser.

    PubMed

    Wu, Hanzhong; Zhang, Fumin; Liu, Tingyang; Balling, Petr; Qu, Xinghua

    2016-05-20

    In this paper, we develop a multi-heterodyne system capable of absolute distance measurement using a frequency comb and a tunable diode laser locked to a Fabry-Perot cavity. In a series of subsequent measurements, numerous beat components can be obtained by downconverting the optical frequency into the RF region with multi-heterodyne interferometry. The distances can be measured via the mode phases with a series of synthetic wavelengths. The comparison with the reference interferometer shows an agreement within 1.5 μm for the averages of five measurements and 2.5 μm for the single measurement, which is at the 10-8 relative precision level. PMID:27411152

  15. Comb-locked cavity ring-down spectrometer

    NASA Astrophysics Data System (ADS)

    Gatti, Davide; Sala, Tommaso; Gotti, Riccardo; Cocola, Lorenzo; Poletto, Luca; Prevedelli, Marco; Laporta, Paolo; Marangoni, Marco

    2015-02-01

    Extreme frequency accuracy and high sensitivity are obtained with a novel comb-locked cavity-ring-down spectrometer operating in the near-infrared from 1.5 to 1.63 μm. A key feature of our approach is the tight frequency locking of the probe laser to the comb, ensuring very high reproducibility and accuracy to the frequency axis upon scanning the comb repetition rate, as well as an efficient light injection into a length-swept high-finesse passive cavity containing the gas sample. Spectroscopic tests on the (30012) ← (00001) P14e line of CO2 at ˜1.57 μm demonstrate an accuracy of ˜17 kHz on the line center frequency in a Doppler broadening regime over the time scale of about 5 min, corresponding to four consecutive spectral scans of the absorption line. Over a single scan, which consists of 1500 spectral points over 75 s, the limit of detection is as low as 5.7 × 10-11 cm-1.

  16. High-precision molecular interrogation by direct referencing of a quantum-cascade-laser to a near-infrared frequency comb.

    PubMed

    Gatti, D; Gambetta, A; Castrillo, A; Galzerano, G; Laporta, P; Gianfrani, L; Marangoni, M

    2011-08-29

    This work presents a very simple yet effective way to obtain direct referencing of a quantum-cascade-laser at 4.3 μm to a near-IR frequency-comb. Precise tuning of the comb repetition-rate allows the quantum-cascade-laser to be scanned across absorption lines of a CO2 gaseous sample and line profiles to be acquired with extreme reproducibility and accuracy. By averaging over 50 acquisitions, line-centre frequencies are retrieved with an uncertainty of 30 kHz in a linear interaction regime. The extension of this methodology to other lines and molecules, by the use of widely tunable extended-cavity quantum-cascade-lasers, paves the way to a wide availability of high-quality and traceable spectroscopic data in the most crucial region for molecular detection and interrogation. PMID:21935118

  17. Efficient generation of twin photons at telecom wavelengths with 2.5 GHz repetition-rate-tunable comb laser.

    PubMed

    Jin, Rui-Bo; Shimizu, Ryosuke; Morohashi, Isao; Wakui, Kentaro; Takeoka, Masahiro; Izumi, Shuro; Sakamoto, Takahide; Fujiwara, Mikio; Yamashita, Taro; Miki, Shigehito; Terai, Hirotaka; Wang, Zhen; Sasaki, Masahide

    2014-01-01

    Efficient generation and detection of indistinguishable twin photons are at the core of quantum information and communications technology (Q-ICT). These photons are conventionally generated by spontaneous parametric down conversion (SPDC), which is a probabilistic process, and hence occurs at a limited rate, which restricts wider applications of Q-ICT. To increase the rate, one had to excite SPDC by higher pump power, while it inevitably produced more unwanted multi-photon components, harmfully degrading quantum interference visibility. Here we solve this problem by using recently developed 10 GHz repetition-rate-tunable comb laser, combined with a group-velocity-matched nonlinear crystal, and superconducting nanowire single photon detectors. They operate at telecom wavelengths more efficiently with less noises than conventional schemes, those typically operate at visible and near infrared wavelengths generated by a 76 MHz Ti Sapphire laser and detected by Si detectors. We could show high interference visibilities, which are free from the pump-power induced degradation. Our laser, nonlinear crystal, and detectors constitute a powerful tool box, which will pave a way to implementing quantum photonics circuits with variety of good and low-cost telecom components, and will eventually realize scalable Q-ICT in optical infra-structures. PMID:25524646

  18. Self-referencable frequency comb from a 170-fs, 1.5-μm solid-state laser oscillator

    NASA Astrophysics Data System (ADS)

    Stumpf, M. C.; Pekarek, S.; Oehler, A. E. H.; Südmeyer, T.; Dudley, J. M.; Keller, U.

    2010-05-01

    We report measurement of the first carrier-envelope offset (CEO) frequency signal from a spectrally broadened ultrafast solid-state laser oscillator operating in the 1.5 μm spectral region. The f-to-2 f CEO frequency beat signal is 49 dB above the noise floor (100-kHz resolution bandwidth) and the free-running linewidth of 3.6 kHz is significantly better than typically obtained by ultrafast fiber laser systems. We used a SESAM mode-locked Er:Yb:glass laser generating 170-fs pulses at a 75 MHz pulse repetition rate with 110-mW average power. It is pumped by one standard telecom-grade 980-nm diode consuming less than 1.5 W of electrical power. Without any further pulse compression and amplification, a coherent octave-spanning frequency comb is generated in a polarization-maintaining highly-nonlinear fiber (PM-HNLF). The fiber length was optimized to yield a strong CEO frequency beat signal between the outer Raman soliton and the spectral peak of the dispersive wave within the supercontinuum. The polarization-maintaining property of the supercontinuum fiber was crucial; comparable octave-spanning supercontinua from two non-PM fibers showed higher intensity noise and poor coherence. A stable CEO-beat was observed even with pulse durations above 200 fs. Achieving a strong CEO frequency signal from relatively long pulses with moderate power levels substantially relaxes the demands on the driving laser, which is particularly important for novel gigahertz diode-pumped solid-state and semiconductor lasers.

  19. Swept Light Sources

    NASA Astrophysics Data System (ADS)

    Johnson, Bart; Atia, Walid; Kuznetsov, Mark; Cook, Christopher; Goldberg, Brian; Wells, Bill; Larson, Noble; McKenzie, Eric; Melendez, Carlos; Mallon, Ed; Woo, Seungbum; Murdza, Randal; Whitney, Peter; Flanders, Dale

    A 1060 nm OEM laser "engine", manufactured by Axsun Technologies, is described. It consists of a swept laser and control electronics coupled with a balanced receiver, k-clock, and a 550 MS/s data acquisition board. The laser's passive mode-locking behavior induced by the rapid wavelength sweep is discussed. As they pass though the gain medium, each pulse is shifted to longer wavelength due to the rise in refractive index associated with gain depletion. New, longer wavelengths, are thus created by nonlinear means rather than by building up anew from spontaneous emission. This nonlinear mechanism enables low noise operation and fast sweep rates. The so-called "coherence revival" phenomenon associated with interference between neighboring mode-locked pulses, is discussed. Typical laser and system data is shown, including k-clock frequency, trigger waveform, pulsed and average output powers and RIN. Receiver and DAQ board noise performance is quantified. The laser RIN is estimated to be lower than -150 dB/Hz. A typical shot-noise-limited sensitivity of 103 dB is achieved for 1.9 mW sample power. The engine is designed for ophthalmic imaging and retinal images from prototype commercial systems are presented.

  20. Interference peak detection based on FPGA for real-time absolute distance ranging with dual-comb lasers

    NASA Astrophysics Data System (ADS)

    Ni, Kai; Dong, Hao; Zhou, Qian; Xu, Mingfei; Li, Xinghui; Wu, Guanhao

    2015-08-01

    Absolute distance measurement using dual femtosecond comb lasers can achieve higher accuracy and faster measurement speed, which makes it more and more attractive. The data processing flow consists of four steps: interference peak detection, fast Fourier transform (FFT), phase fitting and compensation of index of refraction. A realtime data processing system based on Field-Programmable Gate Array (FPGA) for dual-comb ranging has been newly developed. The design and implementation of the interference peak detection algorithm by FPGA and Verilog language is introduced in this paper, which is viewed as the most complicated part and an important guarantee for system precision and reliability. An adaptive sliding window for scanning is used to detect peaks. In the process of detection, the algorithm stores 16 sample data as a detection unit and calculates the average of each unit. The average result is used to determine the vertical center height of the sliding window. The algorithm estimates the noise intensity of each detection unit, and then calculates the average of the noise strength of successive 128 units. The noise average is used to calculate the signal to noise ratio of the current working environment, which is used to adjust the height of the sliding window. This adaptive sliding window helps to eliminate fake peaks caused by noise. The whole design is based on the way of pipeline, which can improves the real-time throughput of the overall peak detection module. Its execution speed is up to 140MHz in the FPGA, and the peak can be detected in 16 clock cycle when it appears.

  1. Efficient optical frequency-comb generator

    NASA Astrophysics Data System (ADS)

    Bell, A. S.; McFarlane, G. M.; Riis, E.; Ferguson, A. I.

    1995-06-01

    We have demonstrated a method that efficiently transfers the power from a single-frequency laser into a wideband frequency comb. The comb was produced by a 2.7-GHz electro-optic modulator in a resonant optical cavity. A coupled cavity technique was used to transfer 8.5% of the laser power into a comb with a span of 400 modes, or more than 1 THz.

  2. Ultra-low phase-noise microwave generation using a diode-pumped solid-state laser based frequency comb and a polarization-maintaining pulse interleaver.

    PubMed

    Portuondo-Campa, Erwin; Buchs, Gilles; Kundermann, Stefan; Balet, Laurent; Lecomte, Steve

    2015-12-14

    We report ultra-low phase-noise microwave generation at a 9.6 GHz carrier frequency from optical frequency combs based on diode-pumped solid-state lasers emitting at telecom wavelength and referenced to a common cavity-stabilized continuous-wave laser. Using a novel fibered polarization-maintaining pulse interleaver, a single-oscillator phase-noise floor of -171 dBc/Hz at 10 MHz offset frequency has been measured with commercial PIN InGaAs photodiodes, constituting a record for this type of detector. Also, a direct optical measurement of the stabilized frequency combs' timing jitter was performed using a balanced optical cross correlator, allowing for an identification of the origin of the phase-noise limitations in the system. PMID:26699033

  3. Ultrafast electrooptic dual-comb interferometry.

    PubMed

    Durán, Vicente; Tainta, Santiago; Torres-Company, Victor

    2015-11-16

    Dual-comb interferometry is a particularly compelling technique that relies on the phase coherence of two laser frequency combs for measuring broadband complex spectra. This method is rapidly advancing the field of optical spectroscopy and empowering new applications, from nonlinear microscopy to laser ranging. Up to now, most dual-comb interferometers were based on modelocked lasers, whose repetition rates have restricted the measurement speed to ~kHz. Here we demonstrate a dual-comb interferometer that is based on electrooptic frequency combs and measures consecutive complex spectra at an ultra-high refresh rate of 25 MHz. These results pave the way for novel scientific and metrology applications of frequency comb generators beyond the realm of molecular spectroscopy, where the measurement of ultrabroadband waveforms is of paramount relevance. PMID:26698533

  4. A stable multi-wavelength PM-EDF laser based on a nonlinear amplifying loop mirror and a TCF comb filter

    NASA Astrophysics Data System (ADS)

    Zou, Hui; Lou, Shuqin; Su, Wei; Han, Bolin

    2014-01-01

    A stable multi-wavelength polarization-maintaining erbium-doped fiber (PM-EDF) ring cavity laser employing a twin-core fiber (TCF) comb filter and a nonlinear amplifying loop mirror (NALM) is proposed and demonstrated. By appropriately adjusting the polarization controllers, the NALM as an amplitude equalizer can effectively reduce the mode competition caused by the homogeneous broadening gain medium in the PM-EDF. Under 150 mW pump power, up to 26 wavelength outputs within a 3 dB bandwidth are achieved and their signal-to-noise ratio (SNR) is 39.5 dB. Besides, the TCF comb filter is experimentally fabricated using a length of 0.78 m TCF spliced between two segments of the single-mode fiber. The transmission spectra of the filter in experimental measurements are in accord with the results of theoretical analysis, and its wavelength spacing is 0.29 nm. Meanwhile, the power fluctuation and wavelength shift are within 0.1 dB and 0.02 nm, respectively. The experimental results indicate that the proposed multi-wavelength fiber laser performs with high stability at room temperature. In addition, the multi-wavelength laser with the TCF comb filter can offer more wavelengths in a 3 dB spectral range and higher SNR than one using a Sagnac loop filter, and the length of the filter is also reduced by more than six times.

  5. Mid-infrared frequency combs

    NASA Astrophysics Data System (ADS)

    Schliesser, Albert; Picqué, Nathalie; Hänsch, Theodor W.

    2012-07-01

    Laser frequency combs are coherent light sources that emit a broad spectrum of discrete, evenly spaced narrow lines whose absolute frequency can be measured to within the accuracy of an atomic clock. Their development in the near-infrared and visible domains has revolutionized frequency metrology while also providing numerous unexpected opportunities in other fields such as astronomy and attosecond science. Researchers are now exploring how to extend frequency comb techniques to the mid-infrared spectral region. Versatile mid-infrared frequency comb generators based on novel laser gain media, nonlinear frequency conversion or microresonators promise to significantly expand the applications of frequency combs. In particular, novel approaches to molecular spectroscopy in the 'fingerprint region', with dramatically improved precision, sensitivity, recording time and/or spectral bandwidth may lead to new discoveries in the various fields relevant to molecular science.

  6. Red, Green, and Blue Astro-combs

    NASA Astrophysics Data System (ADS)

    Phillips, David; Glenday, Alex; Li, Chih-Hao; Korzennik, Sylvain; Noah Chang, Guoqing; Chen, Li-Jin; Benedick, Andrew; Kaertner, Franz; Sasselov, Dimitar; Szentgyorgyi, Andrew; Walsworth, Ronald

    2011-06-01

    Searches for extrasolar planets using the periodic Doppler shift of stellar lines are approaching Earth-like planet sensitivity. Astro-combs, a combination of an octave spanning femtosecond laser and a mode-filtering cavity provide a likely route to increased calibration precision and accuracy. We present results from three astro-combs operating in the red/near-IR, green and blue spectral ranges. Light from a 1-GHz, octave-spanning Ti:Sapphire laser is filtered by a Fabry-Perot Cavity (FPC) constructed from Doubly-Chirped Mirrors to produce a red astro-comb with 100 nm of optical bandwidth. This astro-comb has calibrated an astrophysical spectrograph at the 1 m/s level. In the blue astro-comb, Ti:Sapphire comb light, doubled in a BBO crystal is filtered to 50 GHz mode spacing with an FPC. The blue astro-comb has performed 50 cm/s calibrations. In the ``green'' astro-comb, light from the 1 GHz Ti:Sapphire comb laser is broadened in a photonic crystal fiber optimized to produce light in the green. This 1-GHz spaced green light is then filtered to roughly 40 GHz via an FPC with zero group delay dispersion mirrors, providing approximately 50 nm of astro-comb light centered near 550 nm.

  7. Injection-locked semiconductor laser-based frequency comb for modulation applications in RF analog photonics.

    PubMed

    Sarailou, Edris; Delfyett, Peter

    2016-07-01

    A linearized intensity modulator for periodic and pulsed light is proposed and demonstrated. The free carrier plasma effect has been used to modulate the refractive index of the phase section of a three-section mode-locked laser. If injection locked, the modulation induces an arcsine phase response on the three-section mode-locked laser. By introducing this mode-locked laser into a Mach-Zehnder interferometer biased at quadrature, one can realize a true linear intensity modulation. This novel laser suppresses any unwanted amplitude modulation and increases the performance of the linearized intensity modulator. Experimental results have provided a record low static Iπ of 0.39 mA and a spur-free dynamic range of 75  dB.Hz2/3. PMID:27367083

  8. Noise properties of an optical frequency comb from a SESAM-mode-locked 1.5-μm solid-state laser stabilized to the 10-13 level

    NASA Astrophysics Data System (ADS)

    Schilt, S.; Dolgovskiy, V.; Bucalovic, N.; Schori, C.; Stumpf, M. C.; Di Domenico, G.; Pekarek, S.; Oehler, A. E. H.; Südmeyer, T.; Keller, U.; Thomann, P.

    2012-11-01

    We present a detailed investigation of the noise properties of an optical frequency comb generated from a femtosecond diode-pumped solid-state laser operating in the 1.5-μm spectral region. The stabilization of the passively mode-locked Er:Yb:glass laser oscillator, referred to as ERGO, is achieved using pump power modulation for the control of the carrier envelope offset (CEO) frequency and by adjusting the laser cavity length for the control of the repetition rate. The stability and the noise of the ERGO comb are characterized in free-running and in phase-locked operation by measuring the noise properties of the CEO, of the repetition rate, and of a comb line at 1558 nm. The comb line is analyzed from the heterodyne beat signal with a cavity-stabilized ultra-narrow-linewidth laser using a frequency discriminator. Two different schemes to stabilize the comb to a radio-frequency (RF) reference are compared. The comb properties (phase noise, frequency stability) are limited in both cases by the RF oscillator used to stabilize the repetition rate, while the contribution of the CEO is negligible at all Fourier frequencies, as a consequence of the low-noise characteristics of the CEO-beat. A linewidth of ≈150 kHz and a fractional frequency instability of 4.2×10-13 at 1 s are obtained for an optical comb line at 1558 nm. Improved performance is obtained by stabilizing the comb to an optical reference, which is a cavity-stabilized ultra-narrow linewidth laser at 1558 nm. The fractional frequency stability of 8×10-14 at 1 s, measured in preliminary experiments, is limited by the reference oscillator used in the frequency comparison.

  9. High power frequency comb based on mid-infrared quantum cascade laser at λ ∼ 9 μm

    SciTech Connect

    Lu, Q. Y.; Razeghi, M. Slivken, S.; Bandyopadhyay, N.; Bai, Y.; Zhou, W. J.; Chen, M.; Heydari, D.; Haddadi, A.; McClintock, R.; Amanti, M.; Sirtori, C.

    2015-02-02

    We investigate a frequency comb source based on a mid-infrared quantum cascade laser at λ ∼ 9 μm with high power output. A broad flat-top gain with near-zero group velocity dispersion has been engineered using a dual-core active region structure. This favors the locking of the dispersed Fabry-Pérot modes into equally spaced frequency lines via four wave mixing. A current range with a narrow intermode beating linewidth of 3 kHz is identified with a fast detector and spectrum analyzer. This range corresponds to a broad spectral coverage of 65 cm{sup −1} and a high power output of 180 mW for ∼176 comb modes.

  10. Dynamics of ultra-broadband terahertz quantum cascade lasers for comb operation.

    PubMed

    Li, Hua; Laffaille, Pierre; Gacemi, Djamal; Apfel, Marc; Sirtori, Carlo; Leonardon, Jeremie; Santarelli, Giorgio; Rösch, Markus; Scalari, Giacomo; Beck, Mattias; Faist, Jerome; Hänsel, Wolfgang; Holzwarth, Ronald; Barbieri, Stefano

    2015-12-28

    We present an experimental investigation of the multimode dynamics and the coherence of terahertz quantum cascade lasers emitting over a spectral bandwidth of ~1THz. The devices are studied in free-running and under direct RF modulation. Depending on the pump current we observe different regimes of operation, where RF spectra displaying single and multiple narrow beat-note signals alternate with spectra showing a single beat-note characterized by an intense phase-noise, extending over a bandwidth up to a few GHz. We investigate the relation between this phase-noise and the dynamics of the THz modes through the electro-optic sampling of the laser emission. We find that when the phase-noise is large, the laser operates in an unstable regime where the lasing modes are incoherent. Under RF modulation of the laser current such instability can be suppressed and the modes coherence recovered, while, simultaneously, generating a strong broadening of the THz emission spectrum. PMID:26831993

  11. Discerning comb and Fourier mean frequency from an fs laser based on the principle of non-interaction of waves

    NASA Astrophysics Data System (ADS)

    Roychoudhuri, Chandrasekhar; Prasad, Narasimha

    2012-02-01

    time finite model of a photon. QM only predicts that EM energy emission (spontaneous and stimulated) takes place only in a discrete amount at a time from atoms and molecules. It does not give us recipe about how to visualize a propagating photon as it expands diffractively. However, Huygens-Fresnel's classical diffraction integral gives us a rigorous model, which is the cornerstone of modeling evolution of laser cavity modes, CW or pulsed. In this paper, we highlight the contradictions that arise out of the prevailing mode-lock theory and resolve them by using causal models, already underscored above. For example, there are now a wide range of very successful technological applications of the frequency comb extracted out of fs lasers. If the Fourier summation were the correct physical process, then all the cavity modes would have been summed (converted) into a single mean frequency around the gain line center for perfectly mode-locked systems. Further, sending such fs pulses through an optical spectrometer would have always displayed a transform limited fringe, centering on the mean Fourier frequency, rather than generating the comb frequencies, albeit instrumentally broadened. Output pulse train from a phase locked laser is functionally produced due to the oscillatory time-gating behavior of the intra-cavity phase-locking devices. So, we need to pay more attention to the fast temporal behavior of the materials we use for achieving very fast time-gating, since this material imposes phase locking on the cavity modes to enhance its own high-contrast time-gating behavior.

  12. Self-referenceable frequency comb from a gigahertz diode-pumped solid-state laser

    NASA Astrophysics Data System (ADS)

    Pekarek, Selina; Südmeyer, Thomas; Lecomte, Steve; Kundermann, Stefan; Dudley, John M.; Keller, Ursula

    2011-08-01

    We present carrier envelope offset (CEO) frequency detection of a diode-pumped Yb:KGW (ytterbium-doped potassium gadolinium tungstate) laser with a repetition rate of 1 GHz. The SESAM-soliton-modelocked laser delivers 2.2-W average power in 290-fs pulses. This corresponds to a peak power of 6.7 kW and the optical-to-optical efficiency is 38%. With a passive pulse compression the duration is reduced to 100 fs at an average power of 1.1 W. Coherent supercontinuum (SC) generation in a highly nonlinear photonic crystal fiber (PCF) is achieved without additional amplification. Furthermore we have demonstrated that pulse compression towards lower soliton orders of approximately 10 was required for coherent SC generation and CEO detection. Additional numerical simulations further confirm these experimental results.

  13. Generation of efficient 20 GHz optical combs in a Brillouin-erbium fiber laser

    NASA Astrophysics Data System (ADS)

    Parvizi, R.; Shahabuddin, N. S.; Ali, N. M.; Harun, S. W.; Emami, S. D.; Vaseghi, B.; Ahmad, H.

    2013-01-01

    A tunable multiwavelength Brillouin-erbium fiber laser is experimentally demonstrated with a double-Brillouin-frequency spacing. This double-frequency shifter is constructed by incorporating a four-port circulator to isolate and circulate the odd-Stokes signals through the 10 km long non-zero dispersion shifted fiber, which acts as a Brillouin gain medium. The output even-order Stokes signals are amplified in the erbium gain block formed in a ring cavity. Up to 15 lasing lines with a wavelength spacing of 0.173 nm have been achieved at a 980 nm pump power of 50 mW and a Brillouin pump of 3 dB m. The multiwavelength laser source exhibits a 10 nm tuning range from 1552 to 1562 nm with the optical signal-to-noise ratio of the desired output channels at around 34.5 dB.

  14. Inter-comb synchronization by mode-to-mode locking

    NASA Astrophysics Data System (ADS)

    Chun, Byung Jae; Kim, Young-Jin; Kim, Seung-Woo

    2016-08-01

    Two combs of fiber femtosecond lasers are synchronized through the optical frequency reference created by injection-locking of a diode laser to a single comb mode. Maintaining a mHz-level narrow linewidth, the optical frequency reference permits two combs to be stabilized by mode-to-mode locking with a relative stability of 1.52  ×  10‑16 at 10 s with a frequency slip of 2.46 mHz. This inter-comb synchronization can be utilized for applications such as dual-comb spectroscopy or ultra-short pulse synthesis without extra narrow-linewidth lasers.

  15. Scaling of Yb-Fiber Frequency Combs

    NASA Astrophysics Data System (ADS)

    Ruehl, Axel; Marcinkevicius, Andrius; Fermann, Martin E.; Hartl, Ingmar

    2010-06-01

    Immediately after their introduction in 1999, femtosecond laser frequency combs revolutionized the field of precision optical frequency metrology and are key elements in many experiments. Frequency combs based on femtosecond Er-fiber lasers based were demonstrated in 2005, allowing additionally rugged, compact set-ups and reliable unattended long-term operation. The introduction of Yb-fiber technology led to an dramatic improvement in fiber-comb performance in various aspects. Low-noise Yb-fiber femtosecond oscillators enabled a reduction of relative comb tooth linewidth to the sub-Hz level as well as scaling of the fundamental comb spacings up to 1 GHz. This is beneficial for any frequency-domain comb application due to the higher power per comb-mode. Many spectroscopic applications require, however, frequency combs way beyond the wavelength range accessible with broad band laser materials, so nonlinear conversion and hence higher peak intensity is required. We demonstrated power scaling of Yb-fiber frequency combs up to 80 W average power in a strictly linear chirped-pulse amplification schemes compatible with low-noise phase control. These high-power Yb-fiber-frequency combs facilitated not only the extension to the mid-IR spectral region. When coupled to a passive enhancement cavity, the average power can be further scaled to the kW-level opening new capabilities for XUV frequency combs via high-harmonic generation. All these advances of fiber-based frequency combs will trigger many novel applications both in fundamental and applied sciences. Schibli et al., Nature Photonics 2 355 (2008). Hartl et al., MF9 in Advanced Solid-State Photonics. 2009, Optical Society of America. Ruehl et al., AWC7 in Advanced Solid-State Photonics. 2010, Optical Society of America. Adler et al., Optics Letters 34 1330 (2009). Yost et al., Nature Physics 5 815 (2009).

  16. Coarse frequency comb interferometry

    NASA Astrophysics Data System (ADS)

    Schwider, J.

    2008-08-01

    Real wedge interferometers of the Fizeau-type do not allow for fringes in case of a spectral broad band source - or in short: for white light fringes. Here, the use of a suitable frequency comb source will help to overcome this limitation on the one hand and on the other will offer the capability for enhanced phase sensitivity in high precision measurements of surface deviations. Frequency combs can be produced either by using a pulse train from a fs-laser or by passive filtering of the light emitted by a broad band source as a superlum-diode or a fs-laser. The frequency comb produced by a common fs-laser is extremely fine, i.e., the frequency difference of consecutive peaks is very small or the distance of consecutive pulses of the pulse train might be of the order of 1m. Therefore, the coarse pulse train produced by passive filtering of a broad band source is better adapted to the needs of surface testing interferometers. White light fringes are either applied for the profiling of discontinuous surfaces and/or can serve as an indication for the correct choice of multiplication factors in superposition interferometry. During the last decennium it became more and more clear that spatially incoherent sources provide better measuring accuracy in surface measurements due to the reduced influence of dust diffraction patterns. The advantage of laser illumination can nevertheless be maintained if the laser light is made spatially incoherent through moving scatterers in the light path. Here, we will discuss the application of spatially incoherent broad band light frequency filtered through a Fabry-Perot filter. The main applications are in the following fields: (1) surface profiling applications using two-beam Fizeau interferometers, (2) selection of single cavities out of a series of interlaced cavities, and (3) sensitivity enhancement for multi-beam interferometers for planeness or sphericity measurements. Some of the discussed possibilities will be experimentally

  17. Improved signal-to-noise ratio of 10 GHz microwave signals generated with a mode-filtered femtosecond laser frequency comb.

    PubMed

    Diddams, S A; Kirchner, M; Fortier, T; Braje, D; Weiner, A M; Hollberg, L

    2009-03-01

    We use a Fabry-Perot cavity to optically filter the output of a Ti:sapphire frequency comb to integer multiples of the original 1 GHz mode spacing. This effectively increases the pulse repetition rate, which is useful for several applications. In the case of low-noise microwave signal generation, such filtering leads to improved linearity of the high-speed photodiodes that detect the mode-locked laser pulse train. The result is significantly improved signal-to-noise ratio at the 10 GHz harmonic with the potential for a shot-noise limited single sideband phase noise floor near -168 dBc/Hz. PMID:19259170

  18. 6-GHz, Kerr-lens mode-locked Yb:Lu2O3 ceramic laser for comb-resolved broadband spectroscopy.

    PubMed

    Endo, Mamoru; Ozawa, Akira; Kobayashi, Yohei

    2013-11-01

    A laser diode (LD)-pumped, 6-GHz repetition rate, ytterbium (Yb)-doped Lu2O3 ceramic Kerr-lens mode-locked laser is described. A bow-tie ring cavity enabled the generation of femtosecond pulses centered at a wavelength of 1076 nm with an average power of 10 mW. The pulse duration after an amplifier was 161 fs whereas the transform-limited pulse duration directly from the oscillator was 148 fs. The repetition frequency was sufficiently high for each longitudinal mode to be spectrally resolved by a commercially available optical spectrum analyzer. The developed laser was successfully applied to the absorption spectroscopy of metastable helium4 and demonstrated the suitability of the system as a source for comb-resolved broadband spectroscopy. PMID:24177130

  19. Angiographic imaging using an 18.9 MHz swept-wavelength laser that is phase-locked to the data acquisition clock and resonant scanners (Conference Presentation)

    NASA Astrophysics Data System (ADS)

    Tozburun, Serhat; Blatter, Cedric; Siddiqui, Meena; Nam, Ahhyun S.; Vakoc, Benjamin J.

    2016-03-01

    In this study, we present an angiographic system comprised from a novel 18.9 MHz swept wavelength source integrated with a MEMs-based 23.7 kHz fast-axis scanner. The system provides rapid acquisition of frames and volumes on which a range of Doppler and intensity-based angiographic analyses can be performed. Interestingly, the source and data acquisition computer can be directly phase-locked to provide an intrinsically phase stable imaging system supporting Doppler measurements without the need for individual A-line triggers or post-processing phase calibration algorithms. The system is integrated with a 1.8 Gigasample (GS) per second acquisition card supporting continuous acquisition to computer RAM for 10 seconds. Using this system, we demonstrate phase-stable acquisitions across volumes acquired at 60 Hz frequency. We also highlight the ability to perform c-mode angiography providing volume perfusion measurements with 30 Hz temporal resolution. Ultimately, the speed and phase-stability of this laser and MEMs scanner platform can be leveraged to accelerate OCT-based angiography and both phase-sensitive and phase-insensitive extraction of blood flow velocity.

  20. The Optoelectronic Swept-Frequency Laser and Its Applications in Ranging, Three-Dimensional Imaging, and Coherent Beam Combining of Chirped-Seed Amplifiers

    NASA Astrophysics Data System (ADS)

    Vasilyev, Arseny

    This thesis explores the design, construction, and applications of the optoelectronic swept-frequency laser (SFL). The optoelectronic SFL is a feedback loop designed around a swept-frequency (chirped) semiconductor laser (SCL) to control its instantaneous optical frequency, such that the chirp characteristics are determined solely by a reference electronic oscillator. The resultant system generates precisely controlled optical frequency sweeps. In particular, we focus on linear chirps because of their numerous applications. We demonstrate optoelectronic SFLs based on vertical-cavity surface-emitting lasers (VCSELs) and distributed-feedback lasers (DFBs) at wavelengths of 1550 nm and 1060 nm. We develop an iterative bias current predistortion procedure that enables SFL operation at very high chirp rates, up to 1016 Hz/sec. We describe commercialization efforts and implementation of the predistortion algorithm in a stand-alone embedded environment, undertaken as part of our collaboration with Telaris, Inc. We demonstrate frequency-modulated continuous-wave (FMCW) ranging and three-dimensional (3-D) imaging using a 1550 nm optoelectronic SFL. We develop the technique of multiple source FMCW (MS-FMCW) reflectometry, in which the frequency sweeps of multiple SFLs are "stitched" together in order to increase the optical bandwidth, and hence improve the axial resolution, of an FMCW ranging measurement. We demonstrate computer-aided stitching of DFB and VCSEL sweeps at 1550 nm. We also develop and demonstrate hardware stitching, which enables MS-FMCW ranging without additional signal processing. The culmination of this work is the hardware stitching of four VCSELs at 1550 nm for a total optical bandwidth of 2 THz, and a free-space axial resolution of 75 microns. We describe our work on the tomographic imaging camera (TomICam), a 3-D imaging system based on FMCW ranging that features non-mechanical acquisition of transverse pixels. Our approach uses a combination of

  1. Comb-Net: a high-density WDM network with centralized wavelength combs

    NASA Astrophysics Data System (ADS)

    Gerla, Mario; Chiaretti, Guido; Rotolo, Salvatore

    1993-11-01

    In this paper, we propose Comb-Net, a tree PON architecture in which several laser combs at the root of the tree supply wavelengths to all stations in the PON. Namely, each station receives several wavelengths from comb laser sources located at the root of the PON, via a Comb Distribution network. It then selects (by fixed or tunable filters) some predefined or agreed upon wavelengths, and uses these as sources; i.e., it modulates them (in amplitude or phase) using an external modulator. The modulated wavelengths are then transmitted on the Multiaccess Communications network, which is separate from the Comb Distribution network. The novelty of Comb-Net is to replace the individual (fixed or tunable) lasers at the station with a set of centralized comb generators. The advantages are better stability control, lower noise and potentially lower cost since each station does not require a dedicated source. In the paper, we describe an example of Comb-Net architecture in which the Multiaccess Data network is based on a physical tree topology and on two separate virtual topologies embedded within the physical topology using WDM: a single hop topology used for circuit switched connections; and a multihop topology used for packet switched traffic. We illustrate the Comb-Net architecture with a simple case study.

  2. CEO stabilized frequency comb from a 1-μm Kerr-lens mode-locked bulk Yb:CYA laser.

    PubMed

    Yu, Zijiao; Han, Hainian; Xie, Yang; Peng, Yingnan; Xu, Xiaodong; Wei, Zhiyi

    2016-02-01

    We report the first Kerr-lens mode-locked (KLM) bulk frequency comb in the 1-μm spectral regime. The fundamental KLM Yb:CYA laser is pumped by a low-noise, high-bright 976-nm fiber laser and typically provides 250-mW output power and 57-fs pulse duration. Only 58-mW output pulses were launched into a 1.3-m photonic crystal fiber (PCF) for one octave-spanning supercontinuum generation. Using a simplified collinear f-2f interferometer, the free-running carrier-envelope offset (CEO) frequency was measured to be 42-dB signal-to-noise ratio (SNR) for a 100-kHz resolution and 9.6-kHz full width at half maximum (FWHM) under a 100-Hz resolution. A long-term CEO control at 23 MHz was ultimately realized by feeding the phase error signal to the pump power of the oscillator. The integrated phase noise (IPN) of the locked CEO was measured to be 316 mrad with an integrated range from 1 Hz to 10 MHz. The standard deviation and Allan deviation for more than 4-hour recording are 1.6 mHz and 5.6 × 10(-18) (for 1-s gate time), respectively. This is, to the best of our knowledge, the best stability achieved among the 1-μm solid-state frequency combs. PMID:26906875

  3. 100 kHz axial scan rate swept-wavelength OCT using sampled grating distributed Bragg reflector lasers

    NASA Astrophysics Data System (ADS)

    O'Connor, Shane; Bernacil, Michael A.; DeKelaita, Andrew; Maher, Ben; Derickson, Dennis

    2009-02-01

    Fast wavelength tunable sampled grating distributed Bragg reflector (SG-DBR) lasers are used to generate fast, linear, continuous wavelength sweeps. High resolution wavelength sweeps in excess of 45 nm are demonstrated at a 100 kHz repetition rate. The front mirror, back mirror and phase segment tuning segments can be modulated at very fast rates, which allows for very fast wavelength ramp rates. This sweep is generated through three time synchronized current versus time waveforms applied to the back mirror, front mirror and phase sections of the laser. The sweep consists of fifty separate mode-hop-free tuning segments which are stitched together to form a near continuous wavelength ramp. The stitching points require a maximum of 60 ns for amplitude, wavelength, and thermal settling time to allow the laser to equilibrate. Wavelength tuning non-linearities, output power wavelength dependency, and wavelength discontinuities are defects in the wavelength sweep that result from properties of the wavelength tuning mechanism as well as limitations of the signal generators that produce the time varying bias currents. A Michelson Interferometer is used to examine the effects of these defects for optical coherence tomography (OCT). The OCT measurements demonstrate spectral broadening of the source and interference signal reduction as the penetration depth increases. However, these effects are not very severe for delay differences less than 2 mm even without correction for sweep nonlinearities.

  4. Recent advances in ultrafast optical parametric oscillator frequency combs

    NASA Astrophysics Data System (ADS)

    McCracken, Richard A.; Zhang, Zhaowei; Reid, Derryck T.

    2014-12-01

    We discuss recent advances in the stabilization and application of femtosecond frequency combs based on optical parametric oscillators (OPOs) pumped by femtosecond lasers at 800 and 1060 nm. A method for locking to zero the carrier-envelope-offset of a Ti:sapphire-pumped OPO comb is described. The application of Yb:KYW-laser-pumped dual-combs for mid-infrared spectroscopy is detailed, specifically methane spectroscopy at approximately a 0.7% concentration at 1 atm.

  5. Precision Rvs In The Nir: First On-sky Velocities With A U/ne Lamp And A Laser Frequency Comb

    NASA Astrophysics Data System (ADS)

    Mahadevan, Suvrath; Ramsey, L.; Redman, S.; Bender, C.; Terrien, R.; Roy, A.; Botzer, B.; Osterman, S.; Diddams, S.; Ycas, G.; Quinlan, F.

    2011-09-01

    Precision radial velocities in the near infrared (NIR) can help detect terrestrial mass planets around mid and late M dwarfs that are typically too faint in the optical for effective monitoring. The NIR poses a new set of calibration and technology challenges. We will discuss the current state of the art in NIR spectroscopy, and RV precision and present ongoing work at Penn State with the Pathfinder NIR testbed. With the Pathfinder we have demonstrated 10-20 m/s radial velocity precision in the NIR Y band at the 9m Hobby Eberly telescope using a Uranium-Neon hollow cathode lamp as a simultaneous wavelength reference. We shall present these results and also new velocity results from recent first on-sky observations with an H band laser frequency comb developed at NIST and CASA. The innate stability and known frequencies of the comb lines provides an excellent calibrator in the H band, but numerous systematics like fiber modal noise, tellurics, and detector calibration need to be overcome. We will discuss progress made on all these fronts with experiments on the Pathfinder testbed. We acknowledge support from NSF, NASA, NAI, NIST, Penn State, and the Center for Exoplanets & Habitable Worlds.

  6. Optical-pulse generation and compression using a comb-driven gain-switched laser diode and chromatic-dispersion compensator

    NASA Astrophysics Data System (ADS)

    Arora, Sumeeta

    Gain-switching is a technique to generate short-width optical pulses. Its main advantage is that it does not require any change in the circuitry of the laser diode used or employ an external optical modulator. The modulating signal generator used by previous studies of gain-switching is an RF sine wave source or a comb generator. Previous work on gain-switching using comb generators as input source have selected only a single value of temporal period. For the first time, we study of the dependence of the optical pulsewidth and peak power of gain-switched pulses as a function of the temporal period using a comb generator. We find a baseline optical pulse width at large temporal periods, and that this width decreases by approximately 3% as the temporal period is reduced. The width then increases for even shorter temporal periods. To conclude, there is a region of operation in the temporal period range where a minimum gain-switched pulsewidth can be obtained. The dependence of pulsewidth on the magnitude of DC bias and modulating signal applied is also studied. It is seen that the pulsewidth decreases with the increase in the values of both these currents. But there is a drawback of increasing the magnitude of the applied current that is mostly neglected in the scientific literature; at higher values of applied current, ripples are observed in the gain-switched optical pulses. For the first time, we study gain-switched pulses using a non-regular, data-like pattern "1011" as the modulating signal. The width of the input signal is varied to study the impact on the gain-switched pulses. It is seen that for lower width input signals, a higher value of DC bias is required to obtain optical pulses for the whole data pattern. But for higher width input signal, the whole data pattern is obtained as optical pulses at lower values of DC bias. Moreover, the gain-switched pulses are not uniform in terms of peak power, and we explore means to make these power levels uniform. For

  7. Modeling Frequency Comb Sources

    NASA Astrophysics Data System (ADS)

    Li, Feng; Yuan, Jinhui; Kang, Zhe; Li, Qian; Wai, P. K. A.

    2016-06-01

    Frequency comb sources have revolutionized metrology and spectroscopy and found applications in many fields. Stable, low-cost, high-quality frequency comb sources are important to these applications. Modeling of the frequency comb sources will help the understanding of the operation mechanism and optimization of the design of such sources. In this paper,we review the theoretical models used and recent progress of the modeling of frequency comb sources.

  8. Shock Characteristics Measured Upstream of Both a Forward-Swept and an Aft-Swept Fan

    NASA Technical Reports Server (NTRS)

    Podboy, Gary G.; Krupar, Martin J.; Sutliff, Daniel L.; Horvath, Csaba

    2007-01-01

    Three different types of diagnostic data-blade surface flow visualization, shroud unsteady pressure, and laser Doppler velocimeter (LDV)--were obtained on two fans, one forward-swept and one aft-swept, in order to learn more about the shocks which propagate upstream of these rotors when they are operated at transonic tip speeds. Flow visualization data are presented for the forward-swept fan operating at 13831 rpm(sub c), and for the aft-swept fan operating at 12500 and 13831 rpm(sub c) (corresponding to tip rotational Mach numbers of 1.07 and 1.19, respectively). The flow visualization data identify where the shocks occur on the suction side of the rotor blades. These data show that at the takeoff speed, 13831 rpm(sub c), the shocks occurring in the tip region of the forward-swept fan are further downstream in the blade passage than with the aft-swept fan. Shroud unsteady pressure measurements were acquired using a linear array of 15 equally-spaced pressure transducers extending from two tip axial chords upstream to 0.8 tip axial chords downstream of the static position of the tip leading edge of each rotor. Such data are presented for each fan operating at one subsonic and five transonic tip speeds. The unsteady pressure data show relatively strong detached shocks propagating upstream of the aft-swept rotor at the three lowest transonic tip speeds, and weak, oblique pressure disturbances attached to the tip of the aft-swept fan at the two highest transonic tip speeds. The unsteady pressure measurements made with the forward-swept fan do not show strong shocks propagating upstream of that rotor at any of the tested speeds. A comparison of the forward-swept and aft-swept shroud unsteady pressure measurements indicates that at any given transonic speed the pressure disturbance just upstream of the tip of the forward-swept fan is much weaker than that of the aft-swept fan. The LDV data suggest that at 12500 and 13831 rpm(sub c), the forward-swept fan swallowed the

  9. Efficient generation of twin photons at telecom wavelengths with 2.5 GHz repetition-rate-tunable comb laser

    PubMed Central

    Jin, Rui-Bo; Shimizu, Ryosuke; Morohashi, Isao; Wakui, Kentaro; Takeoka, Masahiro; Izumi, Shuro; Sakamoto, Takahide; Fujiwara, Mikio; Yamashita, Taro; Miki, Shigehito; Terai, Hirotaka; Wang, Zhen; Sasaki, Masahide

    2014-01-01

    Efficient generation and detection of indistinguishable twin photons are at the core of quantum information and communications technology (Q-ICT). These photons are conventionally generated by spontaneous parametric down conversion (SPDC), which is a probabilistic process, and hence occurs at a limited rate, which restricts wider applications of Q-ICT. To increase the rate, one had to excite SPDC by higher pump power, while it inevitably produced more unwanted multi-photon components, harmfully degrading quantum interference visibility. Here we solve this problem by using recently developed 10 GHz repetition-rate-tunable comb laser, combined with a group-velocity-matched nonlinear crystal, and superconducting nanowire single photon detectors. They operate at telecom wavelengths more efficiently with less noises than conventional schemes, those typically operate at visible and near infrared wavelengths generated by a 76 MHz Ti Sapphire laser and detected by Si detectors. We could show high interference visibilities, which are free from the pump-power induced degradation. Our laser, nonlinear crystal, and detectors constitute a powerful tool box, which will pave a way to implementing quantum photonics circuits with variety of good and low-cost telecom components, and will eventually realize scalable Q-ICT in optical infra-structures. PMID:25524646

  10. Linewidth of the harmonics in a microwave frequency comb generated by focusing a mode-locked ultrafast laser on a tunneling junction

    SciTech Connect

    Hagmann, Mark J.; Stenger, Frank S.; Yarotski, Dmitry A.

    2013-12-14

    Previous analyses suggest that microwave frequency combs (MFCs) with harmonics having extremely narrow linewidths could be produced by photodetection with a mode-locked ultrafast laser. In the MFC generated by focusing a passively mode-locked ultrafast laser on a tunneling junction, 200 harmonics from 74.254 MHz to 14.85 GHz have reproducible measured linewidths approximating the 1 Hz resolution bandwidth (RBW) of the spectrum analyzer. However, in new measurements at a RBW of 0.1 Hz, the linewidths are distributed from 0.12 to 1.17 Hz. Measurements and analysis suggest that, because the laser is not stabilized, the stochastic drift in the pulse repetition rate is the cause for the distribution in measured linewidths. It appears that there are three cases in which the RBW is (1) greater than, (2) less than, or (3) comparable with the intrinsic linewidth. The measured spectra in the third class are stochastic and may show two or more peaks at a single harmonic.

  11. Efficient generation of twin photons at telecom wavelengths with 2.5 GHz repetition-rate-tunable comb laser

    NASA Astrophysics Data System (ADS)

    Jin, Rui-Bo; Shimizu, Ryosuke; Morohashi, Isao; Wakui, Kentaro; Takeoka, Masahiro; Izumi, Shuro; Sakamoto, Takahide; Fujiwara, Mikio; Yamashita, Taro; Miki, Shigehito; Terai, Hirotaka; Wang, Zhen; Sasaki, Masahide

    2014-12-01

    Efficient generation and detection of indistinguishable twin photons are at the core of quantum information and communications technology (Q-ICT). These photons are conventionally generated by spontaneous parametric down conversion (SPDC), which is a probabilistic process, and hence occurs at a limited rate, which restricts wider applications of Q-ICT. To increase the rate, one had to excite SPDC by higher pump power, while it inevitably produced more unwanted multi-photon components, harmfully degrading quantum interference visibility. Here we solve this problem by using recently developed 10 GHz repetition-rate-tunable comb laser, combined with a group-velocity-matched nonlinear crystal, and superconducting nanowire single photon detectors. They operate at telecom wavelengths more efficiently with less noises than conventional schemes, those typically operate at visible and near infrared wavelengths generated by a 76 MHz Ti Sapphire laser and detected by Si detectors. We could show high interference visibilities, which are free from the pump-power induced degradation. Our laser, nonlinear crystal, and detectors constitute a powerful tool box, which will pave a way to implementing quantum photonics circuits with variety of good and low-cost telecom components, and will eventually realize scalable Q-ICT in optical infra-structures.

  12. Broadband high-resolution X-ray frequency combs

    NASA Astrophysics Data System (ADS)

    Cavaletto, Stefano M.; Harman, Zoltán; Ott, Christian; Buth, Christian; Pfeifer, Thomas; Keitel, Christoph H.

    2014-07-01

    Optical frequency combs have had a remarkable impact on precision spectroscopy. Enabling this technology in the X-ray domain is expected to result in wide-ranging applications, such as stringent tests of astrophysical models and quantum electrodynamics, a more sensitive search for the variability of fundamental constants, and precision studies of nuclear structure. Ultraprecise X-ray atomic clocks may also be envisaged. In this work, an X-ray pulse-shaping method is proposed to generate a comb in the absorption spectrum of an ultrashort high-frequency pulse. The method employs an optical-frequency-comb laser, manipulating the system's dipole response to imprint a comb on an excited transition with a high photon energy. The described scheme provides higher comb frequencies and requires lower optical-comb peak intensities than currently explored methods, preserves the overall width of the optical comb, and may be implemented using currently available X-ray technology.

  13. Coherence properties of a 2.6-7.5  μm frequency comb produced as a subharmonic of a Tm-fiber laser.

    PubMed

    Smolski, V O; Yang, H; Gorelov, S D; Schunemann, P G; Vodopyanov, K L

    2016-04-01

    We study the temporal coherence of an ultrabroadband frequency comb produced in a degenerate GaAs optical parametric oscillator (OPO) pumped by a stabilized Tm-fiber comb, by observing multiheterodyne beats in the RF domain. We infer that in such a regime the OPO automatically produces a stable frequency comb that is phase and frequency locked to the pump. By varying intracavity dispersion, we achieve a comb spanning 2.6-7.5 μm at a -20  dB level. Low pump threshold (down to 7 mW), high average power (up to 73 mW), broad spectral coverage, flat spectrum, and high coherence make this comb a source suitable for various applications, foremost dual-comb molecular spectroscopy. PMID:27192243

  14. Thermally controlled comb generation and soliton modelocking in microresonators

    NASA Astrophysics Data System (ADS)

    Joshi, Chaitanya; Jang, Jae K.; Luke, Kevin; Ji, Xingchen; Miller, Steven A.; Klenner, Alexander; Okawachi, Yoshitomo; Lipson, Michal; Gaeta, Alexander L.

    2016-06-01

    We report the first demonstration of thermally controlled soliton modelocked frequency comb generation in microresonators. By controlling the electric current through heaters integrated with silicon nitride microresonators, we demonstrate a systematic and repeatable pathway to single- and multi-soliton modelocked states without adjusting the pump laser wavelength. Such an approach could greatly simplify the generation of modelocked frequency combs and facilitate applications such as chip-based dual-comb spectroscopy.

  15. Intelligent Systems for Stabilizing Mode-Locked Lasers and Frequency Combs: Machine Learning and Equation-Free Control Paradigms for Self-Tuning Optics

    NASA Astrophysics Data System (ADS)

    Kutz, J. Nathan; Brunton, Steven L.

    2015-12-01

    We demonstrate that a software architecture using innovations in machine learning and adaptive control provides an ideal integration platform for self-tuning optics. For mode-locked lasers, commercially available optical telecom components can be integrated with servocontrollers to enact a training and execution software module capable of self-tuning the laser cavity even in the presence of mechanical and/or environmental perturbations, thus potentially stabilizing a frequency comb. The algorithm training stage uses an exhaustive search of parameter space to discover best regions of performance for one or more objective functions of interest. The execution stage first uses a sparse sensing procedure to recognize the parameter space before quickly moving to the near optimal solution and maintaining it using the extremum seeking control protocol. The method is robust and equationfree, thus requiring no detailed or quantitatively accurate model of the physics. It can also be executed on a broad range of problems provided only that suitable objective functions can be found and experimentally measured.

  16. Compact electrostatic comb actuator

    DOEpatents

    Rodgers, M. Steven; Burg, Michael S.; Jensen, Brian D.; Miller, Samuel L.; Barnes, Stephen M.

    2000-01-01

    A compact electrostatic comb actuator is disclosed for microelectromechanical (MEM) applications. The actuator is based upon a plurality of meshed electrostatic combs, some of which are stationary and others of which are moveable. One or more restoring springs are fabricated within an outline of the electrostatic combs (i.e. superposed with the moveable electrostatic combs) to considerably reduce the space required for the actuator. Additionally, a truss structure is provided to support the moveable electrostatic combs and prevent bending or distortion of these combs due to unbalanced electrostatic forces or external loading. The truss structure formed about the moveable electrostatic combs allows the spacing between the interdigitated fingers of the combs to be reduced to about one micron or less, thereby substantially increasing the number of active fingers which can be provided in a given area. Finally, electrostatic shields can be used in the actuator to substantially reduce unwanted electrostatic fields to further improve performance of the device. As a result, the compact electrostatic comb actuator of the present invention occupies only a fraction of the space required for conventional electrostatic comb actuators, while providing a substantial increase in the available drive force (up to one-hundred times).

  17. High-power frequency comb in the range of 2-2.15  μm based on a holmium fiber amplifier seeded by wavelength-shifted Raman solitons from an erbium-fiber laser.

    PubMed

    Coluccelli, Nicola; Cassinerio, Marco; Gambetta, Alessio; Laporta, Paolo; Galzerano, Gianluca

    2014-03-15

    We demonstrate a room-temperature high-power frequency comb source covering the spectral region from 2 to 2.15 μm. The source is based on a femtosecond erbium-fiber laser operating at 1.55 μm with a repetition rate of 250 MHz, wavelength-shifted up to 2.06 μm by the solitonic Raman effect, seeding a large-mode-area holmium (Ho) fiber amplifier pumped by a thulium (Tm) fiber laser emitting at 1.94 μm. The frequency comb has an integrated power of 2 W, with overall power fluctuations as low as 0.3%. The beatnote between the comb and a high-spectral-purity, single-frequency Tm-Ho laser has a linewidth of 32 kHz over 1 ms observation time, with a signal-to-noise ratio in excess of 30 dB. PMID:24690863

  18. Forward Swept Compressor Testing

    NASA Technical Reports Server (NTRS)

    Miller, David P.

    1997-01-01

    A new forward-swept rotor designed by Allison Engine Company was tested in NASA Lewis Research Center's CE-18 facility. This testing was a follow-on project sponsored by NASA Lewis to study range enhancements in small turbomachinery. The test was conducted against a baseline rotor design that was also tested in CE-18. The design point for the rotor was a rotor pressure ratio of 2.69, a mass flow of 10.52 lbm/sec, and an adiabatic efficiency of 89.1 percent. Test data indicate that the rotor met the pressure ratio of 2.69 with a 10.77 lbm/sec flow rate, a 87.5-percent adiabatic efficiency, and a 19.5-percent stall margin. The baseline rotor achieved a pressure ratio of 2.69 at a 10.77 lbm/sec flow rate with a stall margin of only 9.2 percent and an adiabatic efficiency of 87.0 percent. The major differences are the significant stall margin increase and the substantially higher off-design peak efficiencies of the forward-swept rotor. The substantially higher performance over the baseline rotor design makes the new design a viable technology candidate for future products.

  19. Integrated Photonic Comb Generation: Applications in Coherent Communication and Sensing

    NASA Astrophysics Data System (ADS)

    Parker, John S.

    Integrated photonics combines many optical components including lasers, modulators, waveguides, and detectors in close proximity via homogeneous (monolithic) or heterogeneous (using multiple materials) integration. This improves stability for interferometers and lasers, reduces the occurrence of unwanted reflections, and it avoids coupling losses between different components as they are on the same chip. Thus, less power is needed to compensate for these added losses, and less heat needs to be removed due to these power savings. In addition, integration allows the many components that comprise a system to be fabricated together, thereby reducing the cost per system and allowing rapid scaling in production throughput. Integrated optical combs have many applications including: metrology, THz frequency generation, arbitrary waveform generation, optical clocks, photonic analog-to-digital converters, sensing (imaging), spectroscopy, and data communication. A comb is a set of optical sources evenly spaced in frequency. Several methods of comb generation including mode-locking and optical parametric oscillation produce phase-matched optical outputs with a fixed phase relationship between the frequency lines. When the absolute frequency of a single comb line is stabilized along with the frequency spacing between comb lines, absolute phase and frequency precision can be achieved over the entire comb bandwidth. This functionality provides tremendous benefits to many applications such as coherent communication and optical sensing. The goals for this work were achieving a broad comb bandwidth and noise reduction, i.e., frequency and phase stability. Integrated mode-locked lasers on the InGaAsP/InP material platform were chosen, as they could be monolithically integrated with the wide range of highly functional and versatile photonic integrated circuits (PICs) previously demonstrated on this platform at UCSB. Gain flattening filters were implemented to increase the comb

  20. Transition frequencies of the D lines of K39 , K40 , and K41 measured with a femtosecond laser frequency comb

    NASA Astrophysics Data System (ADS)

    Falke, Stephan; Tiemann, Eberhard; Lisdat, Christian; Schnatz, Harald; Grosche, Gesine

    2006-09-01

    We report measurements of the transition frequencies 4sS1/22-4pP1/22 and 4sS1/22-4pP3/22 of the potassium isotopes 39, 40, and 41 through an atomic beam experiment with a fractional uncertainty of about 2×10-10 . For frequency calibration, a fs-laser comb referenced to a Cs atomic clock was used. Compared to previous results, hyperfine constants for the states 4pP1/22 and 4pP3/22 and isotope shifts are given with a considerably reduced uncertainty. This paper also resolves the discrepancy of transition frequencies measured by Banerjee [Phys. Rev. A 70, 052505 (2004)] and Scherf [Z. Phys. D 36, 31 (1996)] and the hyperfine constant A(K39,P1/22) reported by Banerjee [Europhys. Lett. 65, 172 (2004)] and Bendali [J. Phys. B 14, 4231 (1981)].

  1. Tunable multi-wavelength thulium-doped fiber laser incorporating two-stage cascaded Sagnac loop comb filter

    NASA Astrophysics Data System (ADS)

    Zhu, Lianqing; He, Wei; Dong, Mingli; Lou, Xiaoping; Luo, Fei

    2016-08-01

    A tunable multi-wavelength narrow-linewidth thulium-doped fiber laser employing two-stage cascaded Sagnac loop mirrors is proposed and experimentally demonstrated. The designed fiber laser is composed of a pump source, wavelength division multiplex, circulator, thulium-doped fiber, polarization controllers (PCs), couplers and polarization-maintaining fibers (PMFs). Two cascaded Sagnac loops are used as the cavity reflector and filter, and the proposed filter is fabricated using two sections of PMFs with 2-m and 1-m lengths, respectively. In the experiment, the laser threshold is 110 mW, and laser can emit single, double, triple, quadruple and quintuple wavelengths in the spectral range of 1873-1901 nm through the simultaneous adjustment of the two PCs. The power fluctuations and 3-dB linewidth are less than 2.1 dB and 0.2 nm, respectively, over 10 min at room temperature, and the side-mode suppression ratio is greater than 20 dB. The proposed laser will be useful in various fields, such as spectral analysis, fiber sensing and optical communication.

  2. Swept-source optical coherence tomography powered by a 1.3-μm vertical cavity surface emitting laser enables 2.3-mm-deep brain imaging in mice in vivo

    NASA Astrophysics Data System (ADS)

    Choi, Woo June; Wang, Ruikang K.

    2015-10-01

    We report noninvasive, in vivo optical imaging deep within a mouse brain by swept-source optical coherence tomography (SS-OCT), enabled by a 1.3-μm vertical cavity surface emitting laser (VCSEL). VCSEL SS-OCT offers a constant signal sensitivity of 105 dB throughout an entire depth of 4.25 mm in air, ensuring an extended usable imaging depth range of more than 2 mm in turbid biological tissue. Using this approach, we show deep brain imaging in mice with an open-skull cranial window preparation, revealing intact mouse brain anatomy from the superficial cerebral cortex to the deep hippocampus. VCSEL SS-OCT would be applicable to small animal studies for the investigation of deep tissue compartments in living brains where diseases such as dementia and tumor can take their toll.

  3. Direct phase-locking of a 8.6-μm quantum cascade laser to a mid-IR optical frequency comb: application to precision spectroscopy of N2O.

    PubMed

    Gambetta, Alessio; Cassinerio, Marco; Coluccelli, Nicola; Fasci, Eugenio; Castrillo, Antonio; Gianfrani, Livio; Gatti, Davide; Marangoni, Marco; Laporta, Paolo; Galzerano, Gianluca

    2015-02-01

    We developed a high-precision spectroscopic system at 8.6 μm based on direct heterodyne detection and phase-locking of a room-temperature quantum-cascade-laser against an harmonic, 250-MHz mid-IR frequency comb obtained by difference-frequency generation. The ∼30  dB signal-to-noise ratio of the detected beat-note together with the achieved closed-loop locking bandwidth of ∼500  kHz allows for a residual integrated phase noise of 0.78 rad (1 Hz-5 MHz), for an ultimate resolution of ∼21  kHz, limited by the measured linewidth of the mid-IR comb. The system was used to perform absolute measurement of line-center frequencies for the rotational components of the ν2 vibrational band of N2O, with a relative precision of 3×10(-10). PMID:25680033

  4. Stabilized chip-scale Kerr frequency comb via a high-Q reference photonic microresonator

    NASA Astrophysics Data System (ADS)

    Lim, Jinkang; Huang, Shu-Wei; Vinod, Abhinav K.; Mortazavian, Parastou; Yu, Mingbin; Kwong, Dim-Lee; Savchenkov, Anatoliy A.; Matsko, Andrey B.; Maleki, Lute; Wong, Chee Wei

    2016-08-01

    We stabilize a chip-scale Si3N4 phase-locked Kerr frequency comb via locking the pump laser to an independent stable high-Q reference microresonator and locking the comb spacing to an external microwave oscillator. In this comb, the pump laser shift induces negligible impact on the comb spacing change. This scheme is a step towards miniaturization of the stabilized Kerr comb system as the microresonator reference can potentially be integrated on-chip. Fractional instability of the optical harmonics of the stabilized comb is limited by the microwave oscillator used for comb spacing lock below 1 s averaging time and coincides with the pump laser drift in the long term.

  5. Blade-to-Blade Variations in Shocks Upstream of Both a Forward-Swept and an Aft-Swept Fan

    NASA Technical Reports Server (NTRS)

    Podboy, Gary G.; Krupar, Martin J.

    2006-01-01

    Detailed laser Doppler velocimeter (LDV) flow field measurements were made upstream of two fans, one forward-swept and one aft-swept, in order to learn more about the shocks which propagate upstream of these rotors when they are operated at supersonic tip speeds. The blade-to-blade variations in the flows associated with these shocks are thought to be responsible for generating Multiple Pure Tone (MPT) noise. The measured blade-to-blade variations are documented in this report through a series of slideshows which show relative Mach number contours computed from the velocity measurements. Data are presented for the forward-swept fan operating at three speeds (corresponding to tip relative Mach numbers of 0.817, 1.074, and 1.189), and for the aft-swept fan operating at two (tip relative Mach numbers of 1.074 and 1.189). These LDV data illustrate how the perturbations in the upstream flow field created by the rotating blades vary with axial position, radial position and rotor speed. As expected, at the highest tested speed the forward-swept fan swallowed the shocks which occur in the tip region, whereas the aftswept fan did not. This resulted in a much smaller flow disturbance just upstream of the tip of the forward-swept fan. Nevertheless, further upstream the two fan flows were much more similar.

  6. Microwave generators simplify swept tests

    NASA Astrophysics Data System (ADS)

    Foster, C. E.; Hagins, M. R.

    1986-01-01

    The utilization of the swept-frequency capability makes it possible to conduct any number of microwave tests. It is pointed out that today's microwave sweepers make such tests simple and straightforward. A filter test involving a high-pass filter with a cutoff frequency of 14.0 GHz is discussed, taking into account the use of a microwave sweeper operating in the range from 12 to 18 GHz. Attention is also given to swept-frequency amplifier testing, antenna swept-gain testing, and microwave antenna testing. With a sweep generator, it is simple to assemble a setup for testing amplifier small-signal gain, flatness, and rolloff.

  7. Phase Stabilization of a Frequency Comb using Multipulse Quantum Interferometry

    NASA Astrophysics Data System (ADS)

    Cadarso, Andrea; Mur-Petit, Jordi; García-Ripoll, Juan José

    2014-02-01

    From the interaction between a frequency comb and an atomic qubit, we derive quantum protocols for the determination of the carrier-envelope offset phase, using the qubit coherence as a reference, and without the need of frequency doubling or an octave spanning comb. Compared with a trivial interference protocol, the multipulse protocol results in a polynomial enhancement of the sensitivity O(N-2) with the number N of laser pulses involved. We specialize the protocols using optical or hyperfine qubits, Λ schemes, and Raman transitions, and introduce methods where the reference is another phase-stable cw laser or frequency comb.

  8. Phase stabilization of a frequency comb using multipulse quantum interferometry.

    PubMed

    Cadarso, Andrea; Mur-Petit, Jordi; García-Ripoll, Juan José

    2014-02-21

    From the interaction between a frequency comb and an atomic qubit, we derive quantum protocols for the determination of the carrier-envelope offset phase, using the qubit coherence as a reference, and without the need of frequency doubling or an octave spanning comb. Compared with a trivial interference protocol, the multipulse protocol results in a polynomial enhancement of the sensitivity O(N-2) with the number N of laser pulses involved. We specialize the protocols using optical or hyperfine qubits, Λ schemes, and Raman transitions, and introduce methods where the reference is another phase-stable cw laser or frequency comb. PMID:24579598

  9. Comb and brush acne.

    PubMed

    Petrozzi, J W

    1980-12-01

    Frequent combing or brushing of the hair may result in an exacerbation of existing acne or be the cause of localized acne. Because of today's hair styling habits and methods, this type of acne is commonly encountered but poorly appreciated by physicians. Patient education is the most important factor in the management of this condition. Comb and brush acne is another external factor to be added to the list of causes of "acne mechanica." PMID:6449356

  10. Kilohertz-Resolution Spectroscopy of Cold Atoms with an Optical Frequency Comb

    SciTech Connect

    Fortier, T. M.; Le Coq, Y.; Stalnaker, J. E.; Diddams, S. A.; Oates, C. W.; Hollberg, L.; Ortega, D.

    2006-10-20

    We have performed sub-Doppler spectroscopy on the narrow intercombination line of cold calcium atoms using the amplified output of a femtosecond laser frequency comb. Injection locking of a 657-nm diode laser with a femtosecond comb allows for two regimes of amplification, one in which many lines of the comb are amplified, and one where a single line is predominantly amplified. The output of the laser in both regimes was used to perform kilohertz-level spectroscopy. This experiment demonstrates the potential for high-resolution absolute-frequency spectroscopy over the entire spectrum of the frequency comb output using a single high-finesse optical reference cavity.

  11. Kilohertz-resolution spectroscopy of cold atoms with an optical frequency comb.

    PubMed

    Fortier, T M; Coq, Y Le; Stalnaker, J E; Ortega, D; Diddams, S A; Oates, C W; Hollberg, L

    2006-10-20

    We have performed sub-Doppler spectroscopy on the narrow intercombination line of cold calcium atoms using the amplified output of a femtosecond laser frequency comb. Injection locking of a 657-nm diode laser with a femtosecond comb allows for two regimes of amplification, one in which many lines of the comb are amplified, and one where a single line is predominantly amplified. The output of the laser in both regimes was used to perform kilohertz-level spectroscopy. This experiment demonstrates the potential for high-resolution absolute-frequency spectroscopy over the entire spectrum of the frequency comb output using a single high-finesse optical reference cavity. PMID:17155398

  12. Adaptive real-time dual-comb spectroscopy

    PubMed Central

    Ideguchi, Takuro; Poisson, Antonin; Guelachvili, Guy; Picqué, Nathalie; Hänsch, Theodor W.

    2014-01-01

    The spectrum of a laser frequency comb consists of several hundred thousand equally spaced lines over a broad spectral bandwidth. Such frequency combs have revolutionized optical frequency metrology and they now hold much promise for significant advances in a growing number of applications including molecular spectroscopy. Despite an intriguing potential for the measurement of molecular spectra spanning tens of nanometres within tens of microseconds at Doppler-limited resolution, the development of dual-comb spectroscopy is hindered by the demanding stability requirements of the laser combs. Here we overcome this difficulty and experimentally demonstrate a concept of real-time dual-comb spectroscopy, which compensates for laser instabilities by electronic signal processing. It only uses free-running mode-locked lasers without any phase-lock electronics. We record spectra spanning the full bandwidth of near-infrared fibre lasers with Doppler-limited line profiles highly suitable for measurements of concentrations or line intensities. Our new technique of adaptive dual-comb spectroscopy offers a powerful transdisciplinary instrument for analytical sciences. PMID:24572636

  13. Adaptive real-time dual-comb spectroscopy.

    PubMed

    Ideguchi, Takuro; Poisson, Antonin; Guelachvili, Guy; Picqué, Nathalie; Hänsch, Theodor W

    2014-01-01

    The spectrum of a laser frequency comb consists of several hundred thousand equally spaced lines over a broad spectral bandwidth. Such frequency combs have revolutionized optical frequency metrology and they now hold much promise for significant advances in a growing number of applications including molecular spectroscopy. Despite an intriguing potential for the measurement of molecular spectra spanning tens of nanometres within tens of microseconds at Doppler-limited resolution, the development of dual-comb spectroscopy is hindered by the demanding stability requirements of the laser combs. Here we overcome this difficulty and experimentally demonstrate a concept of real-time dual-comb spectroscopy, which compensates for laser instabilities by electronic signal processing. It only uses free-running mode-locked lasers without any phase-lock electronics. We record spectra spanning the full bandwidth of near-infrared fibre lasers with Doppler-limited line profiles highly suitable for measurements of concentrations or line intensities. Our new technique of adaptive dual-comb spectroscopy offers a powerful transdisciplinary instrument for analytical sciences. PMID:24572636

  14. Adaptive real-time dual-comb spectroscopy

    NASA Astrophysics Data System (ADS)

    Ideguchi, Takuro; Poisson, Antonin; Guelachvili, Guy; Picqué, Nathalie; Hänsch, Theodor W.

    2014-02-01

    The spectrum of a laser frequency comb consists of several hundred thousand equally spaced lines over a broad spectral bandwidth. Such frequency combs have revolutionized optical frequency metrology and they now hold much promise for significant advances in a growing number of applications including molecular spectroscopy. Despite an intriguing potential for the measurement of molecular spectra spanning tens of nanometres within tens of microseconds at Doppler-limited resolution, the development of dual-comb spectroscopy is hindered by the demanding stability requirements of the laser combs. Here we overcome this difficulty and experimentally demonstrate a concept of real-time dual-comb spectroscopy, which compensates for laser instabilities by electronic signal processing. It only uses free-running mode-locked lasers without any phase-lock electronics. We record spectra spanning the full bandwidth of near-infrared fibre lasers with Doppler-limited line profiles highly suitable for measurements of concentrations or line intensities. Our new technique of adaptive dual-comb spectroscopy offers a powerful transdisciplinary instrument for analytical sciences.

  15. Accurate absolute frequencies of the {nu}{sub 1}+{nu}{sub 3} band of {sup 13}C{sub 2}H{sub 2} determined using an infrared mode-locked Cr:YAG laser frequency comb

    SciTech Connect

    Madej, Alan A.; Bernard, John E.; John Alcock, A.; Czajkowski, Andrzej; Chepurov, Sergei

    2006-04-15

    Absolute frequency measurements, with up to 1x10{sup -11} level accuracies, are presented for 60 lines of the P and R branches for the {nu}{sub 1}+{nu}{sub 3} band of {sup 13}C{sub 2}H{sub 2} at 1.5 {mu}m (194 THz). The measurements were made using cavity-enhanced, diode-laser-based saturation spectroscopy. With one laser system stabilized to the P(16) line and a second laser system stabilized to the line whose frequency was to be determined, a Cr:YAG frequency comb was employed to accurately measure the tetrahertz level frequency intervals. The results are compared with recent work from other groups and indicate that these lines would form a basis for a high-quality atlas of reference frequencies for this region of the spectrum.

  16. Accurate absolute reference frequencies from 1511 to 1545 nm of the {nu}{sub 1}+{nu}{sub 3} band of {sup 12}C{sub 2}H{sub 2} determined with laser frequency comb interval measurements

    SciTech Connect

    Madej, Alan A.; Alcock, A. John; Czajkowski, Andrzej; Bernard, John E.; Chepurov, Sergei

    2006-10-15

    Absolute frequency measurements, with uncertainties as low as 2 kHz (1x10{sup -11}), are presented for the {nu}{sub 1}+{nu}{sub 3} band of {sup 12}C{sub 2}H{sub 2} at 1.5 {mu}m (194-198 THz). The measurements were made using cavity-enhanced, diode-laser-based saturation spectroscopy. With one laser system stabilized to the P(16) line of {sup 13}C{sub 2}H{sub 2} and a system stabilized to the line in {sup 12}C{sub 2}H{sub 2} whose frequency was to be determined, a Cr:YAG laser-based frequency comb was employed to measure the frequency intervals. The systematic uncertainty is notably reduced relative to that of previous studies, and the region of measured lines has been extended. Improved molecular constants are obtained.

  17. Dynamics of comb-of-comb networks

    NASA Astrophysics Data System (ADS)

    Liu, Hongxiao; Lin, Yuan; Dolgushev, Maxim; Zhang, Zhongzhi

    2016-03-01

    The dynamics of complex networks, a current hot topic in many scientific fields, is often coded through the corresponding Laplacian matrix. The spectrum of this matrix carries the main features of the networks' dynamics. Here we consider the deterministic networks which can be viewed as "comb-of-comb" iterative structures. For their Laplacian spectra we find analytical equations involving Chebyshev polynomials whose properties allow one to analyze the spectra in deep. Here, in particular, we find that in the infinite size limit the corresponding spectral dimension goes as ds→2 . The ds leaves its fingerprint on many dynamical processes, as we exemplarily show by considering the dynamical properties of polymer networks, including single monomer displacement under a constant force, mechanical relaxation, and fluorescence depolarization.

  18. Ultrabroadband coherent supercontinuum frequency comb

    SciTech Connect

    Ruehl, Axel; McKay, Hugh; Thomas, Brian; Dong, Liang; Fermann, Martin E.; Hartl, Ingmar; Martin, Michael J.; Cossel, Kevin C.; Chen Lisheng; Benko, Craig; Ye Jun; Dudley, John M.

    2011-07-15

    We present detailed studies of the coherence properties of an ultrabroadband supercontinuum, enabled by a comprehensive approach involving continuous-wave laser sources to independently probe both the amplitude and phase noise quadratures across the entire spectrum. The continuum coherently spans more than 1.5 octaves, supporting Hz-level comparison of ultrastable lasers at 698 nm and 1.54 {mu}m. We present a complete numerical simulation of the accumulated comb coherence in the limit of many pulses, in contrast to the single-pulse level, with systematic experimental verification. The experiment and numerical simulations reveal the presence of quantum-seeded broadband amplitude noise without phase coherence degradation, including the discovery of a dependence of the supercontinuum coherence on the fiber fractional Raman gain.

  19. Optical frequency comb spectroscopy.

    PubMed

    Foltynowicz, A; Masłowski, P; Ban, T; Adler, F; Cossel, K C; Briles, T C; Ye, J

    2011-01-01

    Optical frequency combs offer enormous potential in the detection and control of atoms and molecules by combining their vast spectral coverage with the extremely high spectral resolution of each individual comb component. Sensitive and multiplexed trace gas detection via cavity-enhanced direct frequency comb spectroscopy has been demonstrated for various molecules and applications; however, previous demonstrations have been confined to the visible and near-infrared wavelength range. Future spectroscopic capabilities are created by developing comb sources and spectrometers for the deep ultraviolet and mid-infrared spectral regions. Here we present a broadband high resolution mid-infrared frequency comb-based Fourier transform spectrometer operating in the important molecular fingerprint spectral region of 2100-3600 cm(-1) (2.8-4.8 microm). The spectrometer, employing a multipass cell, allows simultaneous acquisition of broadband, high resolution spectra (down to 0.0035 cm(-1) of many molecular species at concentrations in the part-per-billion range in less than 1 min acquisition time. The system enables precise measurements of concentration even in gas mixtures that exhibit continuous absorption bands. The current sensitivity, 2 x 10(-8) cm(-1) Hz-1/2 per spectral element, is expected to improve by two orders of magnitude with an external enhancement cavity. We have demonstrated this sensitivity increase by combining cavity-enhanced frequency comb spectroscopy with a scanning Fourier transform spectrometer in the near-infrared region and achieving a sensitivity of 4.7 x 10(-10) cm(-1) Hz(-1/2). A cavity-enhanced mid-infrared comb spectrometer will provide a near real-time, high sensitivity, high resolution, precisely frequency calibrated, broad bandwidth system for many applications. PMID:22457942

  20. Coherent Raman dual-comb spectroscopy and imaging

    NASA Astrophysics Data System (ADS)

    Ideguchi, Takuro; Holzner, Simon; Bernhardt, Birgitta; Guelachvili, Guy; Hänsch, Theodor W.; Picqué, Nathalie

    2014-11-01

    The invention of the optical frequency comb technique has revolutionized the field of precision spectroscopy, providing a way to measure the absolute frequency of any optical transition. Since, frequency combs have become common equipment for frequency metrology. In the last decade, novel applications for the optical frequency comb have been demonstrated beyond its original purpose. Broadband molecular spectroscopy is one of those. One such technique of molecular spectroscopy with frequency combs, dual-comb Fourier transform spectroscopy provides short measurement times with resolution and accuracy. Two laser frequency combs with slightly different repetition frequencies generate pairs of pulses with a linearly-scanned delay between pulses in a pair. The system without moving parts mimics a fast scanning Fourier transform interferometer. The measurement speed may be several orders of magnitude faster than that of a Michelson-based Fourier transform spectrometer, which opens up new opportunities for broadband molecular spectroscopy. Recently, dual-comb spectroscopy has been extended to nonlinear phenomena. A broadband Raman spectrum of molecular fingerprints may be measured within a few tens of microseconds with coherent Raman dual-comb spectroscopy. Raster scanning the sample leads to hyperspectral images. This rapid and broadband label-free vibrational spectroscopy and imaging technique might provide new diagnostic methods in a variety of scientific and industrial fields.

  1. Frequency comb metrology with an optical parametric oscillator.

    PubMed

    Balskus, K; Schilt, S; Wittwer, V J; Brochard, P; Ploetzing, T; Jornod, N; McCracken, R A; Zhang, Z; Bartels, A; Reid, D T; Südmeyer, T

    2016-04-18

    We report on the first demonstration of absolute frequency comb metrology with an optical parametric oscillator (OPO) frequency comb. The synchronously-pumped OPO operated in the 1.5-µm spectral region and was referenced to an H-maser atomic clock. Using different techniques, we thoroughly characterized the frequency noise power spectral density (PSD) of the repetition rate frep, of the carrier-envelope offset frequency fCEO, and of an optical comb line νN. The comb mode optical linewidth at 1557 nm was determined to be ~70 kHz for an observation time of 1 s from the measured frequency noise PSD, and was limited by the stability of the microwave frequency standard available for the stabilization of the comb repetition rate. We achieved a tight lock of the carrier envelope offset frequency with only ~300 mrad residual integrated phase noise, which makes its contribution to the optical linewidth negligible. The OPO comb was used to measure the absolute optical frequency of a near-infrared laser whose second-harmonic component was locked to the F = 2→3 transition of the 87Rb D2 line at 780 nm, leading to a measured transition frequency of νRb = 384,228,115,346 ± 16 kHz. We performed the same measurement with a commercial fiber-laser comb operating in the 1.5-µm region. Both the OPO comb and the commercial fiber comb achieved similar performance. The measurement accuracy was limited by interferometric noise in the fibered setup of the Rb-stabilized laser. PMID:27137274

  2. Thermally controlled comb generation and soliton modelocking in microresonators.

    PubMed

    Joshi, Chaitanya; Jang, Jae K; Luke, Kevin; Ji, Xingchen; Miller, Steven A; Klenner, Alexander; Okawachi, Yoshitomo; Lipson, Michal; Gaeta, Alexander L

    2016-06-01

    We report, to the best of our knowledge, the first demonstration of thermally controlled soliton mode-locked frequency comb generation in microresonators. By controlling the electric current through heaters integrated with silicon nitride microresonators, we demonstrate a systematic and repeatable pathway to single- and multi-soliton mode-locked states without adjusting the pump laser wavelength. Such an approach could greatly simplify the generation of mode-locked frequency combs and facilitate applications such as chip-based dual-comb spectroscopy. PMID:27244415

  3. INSTRUMENTS AND METHODS OF INVESTIGATION: New nonlinear laser effects in α-quartz: generation of a two-octave Stokes and anti-Stokes comb and cascaded lasing in the spectral range of the second and third harmonics

    NASA Astrophysics Data System (ADS)

    Kaminskii, A. A.; Bohatý, L.; Becker, P.; Eichler, H. J.; Rhee, H.

    2008-09-01

    Crystals that are simultaneously χ(2)- and χ(3)-active offer a wide range of possibilities for the generation of new coherent wavelengths of light. Frequency conversion processes such as stimulated Raman scattering, second and third harmonic generation, or parametric sum and difference frequency mixing can be combined effectively in the same noncentrosymmetric crystal in cascaded χ(3) <--> χ(2) lasing processes. We present several new manifestations of these effects under picosecond laser excitation in α-quartz (SiO2), the oldest nonlinear-laser crystal. Among them are 45 Stokes and anti-Stokes wavelength comb generation of more than two octaves (from 0.3692 μm to 1.5142 μm) and self-conversion of Raman-generation frequencies into the wavelength region of the second and third harmonics of one-micron pumping via many-step cascaded χ(3) <--> χ(2) processes.

  4. New χ (3)-nonlinear-laser manifestations in tetragonal LuVO4 crystal: more than sesqui-octave Raman-induced Stokes and anti-Stokes comb generation and cascaded self-frequency ``tripling''

    NASA Astrophysics Data System (ADS)

    Kaminskii, A. A.; Rhee, H.; Eichler, H. J.; Ueda, K.; Oka, K.; Shibata, H.

    2008-12-01

    We report the experimental investigations of nonlinear-laser effects in LuVO4 vanadate under one-micron picosecond Nd3+:Y3Al5O12 pumping. In this tetragonal host-crystal for Ln3+ lasants for the first time we excited ultra-broad, more than one and half octave (13500 cm-1) Raman induced Stokes and anti-Stokes generation combs and observed multi-step cascaded parametric χ (3)-lasing in UV spectral region. All generation lines were identified and attributed to SRS-promoting modes of the crystal ( ω SRS1≈900 cm-1 and ω SRS2≈113 cm-1). We classified this vanadate as a promising material for self-Raman laser converters.

  5. Microwave Comb Generator

    NASA Technical Reports Server (NTRS)

    Sigman, E. H.

    1989-01-01

    Stable reference tones aid testing and calibration of microwave receivers. Signal generator puts out stable tones in frequency range of 2 to 10 GHz at all multiples of reference input frequency, at any frequency up to 1 MHz. Called "comb generator" because spectral plot resembles comb. DC reverse-bias current switched on and off at 1 MHz to generate sharp pulses in step-recovery diode. Microwave components mounted on back of special connector containing built-in attenuator. Used in testing microwave and spread-spectrum wide-band receivers.

  6. Dynamics of dual-polarization VCSEL-based optical frequency combs under optical injection locking.

    PubMed

    Prior, E; de Dios, C; Criado, R; Ortsiefer, M; Meissner, P; Acedo, P

    2016-09-01

    The present experimental work studies the dynamics of dual-polarization optical frequency combs (OFCs) based on gain switching (GS) vertical-cavity surface-emitting laser (VCSEL) diodes under optical injection locking (OIL). This study presents two main results. First, we have obtained an overall comb formed by two orthogonally polarized sub-combs with comparable span and power. The overall comb shows enhanced optical span and flatness and high coherence between its modes. The second result is that we have been able to control the polarization state of the overall comb by tuning the polarization state of the injected light by locking the same single teeth of the comb. This produces an overall comb with single polarization that is parallel or orthogonal. These are novel findings that provide for the development of efficient and compact OFCs based on GS VCSEL sources with versatile polarization dynamics. PMID:27607978

  7. Astro-comb calibration of an Echelle Spectrograph

    NASA Astrophysics Data System (ADS)

    Li, C.-H.; Phillips, D. F.; Glenday, A. G.; Benedick, A. J.; Chang, G.; Chen, L.-J.; Cramer, C.; Furesz, G.; Kärtner, F. X.; Sasselov, D.; Szentgyorgyi, A.; Walsworth, R. L.

    2010-07-01

    We describe recent work calibrating a cross-dispersed spectrograph with an "astro-comb" i.e., a high repetition rate, octave spanning femtosecond laser frequency comb; and a filter cavity suppressing laser modes to match the resolution of the spectrograph. Our astro-comb provides ~1500 evenly spaced (~0.6 A) calibration lines of roughly 100 nW per line between 7800 and 8800 Angstroms. The calibration lines of the laser are stabilized to atomic clocks which can be referenced to GPS providing intrinsic stability of the source laser below 1 cm/s in stellar radial velocity sensitivity, as well as long term stability and reproducibility over years. We present calibration of the TRES spectrograph at the 1.5 m telescope at the Fred L Whipple Observatory below 1 m/s radial velocity sensitivity in six orders from 7800-8800 A.

  8. Direct fiber comb stabilization to a gas-filled hollow-core photonic crystal fiber.

    PubMed

    Wu, Shun; Wang, Chenchen; Fourcade-Dutin, Coralie; Washburn, Brian R; Benabid, Fetah; Corwin, Kristan L

    2014-09-22

    We have isolated a single tooth from a fiber laser-based optical frequency comb for nonlinear spectroscopy and thereby directly referenced the comb. An 89 MHz erbium fiber laser frequency comb is directly stabilized to the P(23) (1539.43 nm) overtone transition of (12)C(2)H(2) inside a hollow-core photonic crystal fiber. To do this, a single comb tooth is isolated and amplified from 20 nW to 40 mW with sufficient fidelity to perform saturated absorption spectroscopy. The fractional stability of the comb, ~7 nm away from the stabilized tooth, is shown to be 6 × 10(-12) at 100 ms gate time, which is over an order of magnitude better than that of a comb referenced to a GPS-disciplined Rb oscillator. PMID:25321837

  9. Kerr optical frequency combs: theory, applications and perspectives

    NASA Astrophysics Data System (ADS)

    Chembo, Yanne K.

    2016-06-01

    The optical frequency comb technology is one of the most important breakthrough in photonics in recent years. This concept has revolutionized the science of ultra-stable lightwave and microwave signal generation. These combs were originally generated using ultrafast mode-locked lasers, but in the past decade, a simple and elegant alternativewas proposed,which consisted in pumping an ultra-high-Q optical resonator with Kerr nonlinearity using a continuous-wave laser. When optimal conditions are met, the intracavity pump photons are redistributed via four-wave mixing to the neighboring cavity modes, thereby creating the so-called Kerr optical frequency comb. Beyond being energy-efficient, conceptually simple, and structurally robust, Kerr comb generators are very compact devices (millimetric down to micrometric size) which can be integrated on a chip. They are, therefore, considered as very promising candidates to replace femtosecond mode-locked lasers for the generation of broadband and coherent optical frequency combs in the spectral domain, or equivalently, narrow optical pulses in the temporal domain. These combs are, moreover, expected to provide breakthroughs in many technological areas, such as integrated photonics, metrology, optical telecommunications, and aerospace engineering. The purpose of this review article is to present a comprehensive survey of the topic of Kerr optical frequency combs.We provide an overview of the main theoretical and experimental results that have been obtained so far. We also highlight the potential of Kerr combs for current or prospective applications, and discuss as well some of the open challenges that are to be met at the fundamental and applied level.

  10. Polarization-maintaining buffered Fourier domain mode-locked swept source for optical coherence tomography

    PubMed Central

    Zhang, Jun; Jing, Joe; Wang, Pinghe; Chen, Zhongping

    2012-01-01

    A polarization-maintaining buffered Fourier domain mode-locked (FDML) swept source with a center wavelength of 1300 nm is demonstrated. The scanning rate of the buffered FDML swept source is doubled without sacrificing the output power of the swept source by combining two orthogonally polarized outputs with a polarization beam combiner. The stability of the swept source is improved because the polarization state of the laser beam inside the laser cavity is maintained without the use of any polarization controllers. The swept source is capable of an edge-to-edge tuning range of more than 150 nm and a FWHM range of 95 nm at a 102 kHz sweeping rate and with an average power of 12 mW. A swept source optical coherence tomography (SSOCT) system is developed utilizing this buffered FDML swept source. The axial resolution of the SSOCT system is measured to be 9.4 μmin air. The sensitivity of the SSOCT system is 107.5 dB at a depth of 0.25 mm with a 6 dB roll-off at a depth of 2.25 mm. PMID:22179884