Showing papers on "Femtosecond pulse shaping published in 2014"
TL;DR: The generation of a femtosecond pulse in a fiber ring laser by using a polyvinyl alcohol (PVA)-based molybdenum disulfide (MoS(2) SA) saturable absorber indicates that the filmy PVA-based MoS( 2) SA is indeed a good candidate for an ultrafast saturable absorption device.
Abstract: We report on the generation of a femtosecond pulse in a fiber ring laser by using a polyvinyl alcohol (PVA)-based molybdenum disulfide (MoS2) saturable absorber (SA). With a saturable optical intensity of 34 MW/cm2 and a modulation depth of ∼4.3%, the PVA-based MoS2 SA had been employed with an erbium-doped fiber ring laser as a mode locker. The mode-locking operation could be achieved at a low pump threshold of 22 mW. A ∼710 fs pulse centered at 1569.5 nm wavelength with a repetition rate of 12.09 MHz had been achieved with proper cavity dispersion. With the variation of net cavity dispersion, output pulses with durations from 0.71 to 1.46 ps were obtained. The achievement of a femtosecond pulse at 1.55 μm waveband demonstrates the broadband saturable absorption of MoS2, and also indicates that the filmy PVA-based MoS2 SA is indeed a good candidate for an ultrafast saturable absorption device.
351 citations
TL;DR: The experimental results demonstrate that the PVA could be an excellent host material for fabricating high-performance TISA, and indicate that the filmy PVA-TISA is indeed a good candidate for ultrafast saturable absorption device.
Abstract: We reported on the generation of femtosecond pulse in a fiber ring laser by using a polyvinyl alcohol (PVA)-based topological insulator (TI), Bi2Se3 saturable absorber (SA). The PVA-TI composite has a low saturable optical intensity of 12 MW/cm2 and a modulation depth of ~3.9%. By incorporating the fabricated PVA-TISA into a fiber laser, mode-locking operation could be achieved at a low pump threshold of 25 mW. After an optimization of the cavity parameters, optical pulse with ~660 fs centered at 1557.5 nm wavelength had been generated. The experimental results demonstrate that the PVA could be an excellent host material for fabricating high-performance TISA, and also indicate that the filmy PVA-TISA is indeed a good candidate for ultrafast saturable absorption device.
253 citations
TL;DR: With this new milestone result, this work has successfully scaled the pulse energy of ultrafast laser oscillators to a new performance regime and can predict that pulse energies of several hundreds of microjoules will become possible in the near future.
Abstract: We present a semiconductor saturable absorber mirror (SESAM) mode-locked thin-disk laser generating 80 μJ of pulse energy without additional amplification. This laser oscillator operates at a repetition rate of 3.03 MHz and delivers up to 242 W of average output power with a pulse duration of 1.07 ps, resulting in an output peak power of 66 MW. In order to minimize the parasitic nonlinearity of the air inside the laser cavity, the oscillator was operated in a vacuum environment. To start and stabilize soliton mode locking, we used an optimized high-damage threshold, low-loss SESAM. With this new milestone result, we have successfully scaled the pulse energy of ultrafast laser oscillators to a new performance regime and can predict that pulse energies of several hundreds of microjoules will become possible in the near future. Such lasers are interesting for both industrial and scientific applications, for example for precise micromachining and attosecond science.
176 citations
20 Dec 2014
TL;DR: In this paper, a femtosecond supercontinuum was generated in a solid medium with pulse energy and mode quality that approach those generated in the gas phase while preserving the advantages of a condensed medium of being compact, simple to operate, and highly reproducible.
Abstract: Destructive nonlinear processes have limited the useful input power to a few megawatts for supercontinuum generation in bulk material. Consequently, reliable high-power, high-pulse-energy supercontinuum in condensed media has not been realized. Here, we describe an intense femtosecond supercontinuum generated in a solid medium with pulse energy and mode quality that approach those generated in the gas phase while preserving the advantages of a condensed medium of being compact, simple to operate, and highly reproducible. This is achieved by strategically placing several thin solid plates at or near the focused waist of a high-power laser pulse. The thickness of each plate is such that the optical pulse exits the plate before undesirable effects begin to take hold of the pulse. With this approach, we have obtained pulses that have an octave-spanning spectrum that covers from 450 to 980 nm at the −20 dB intensity level while converting as much as 54% of the input pulse energy to the continuum. The highest pulse energy obtained to date is 76 μJ, nearly two orders of magnitude greater than previously reported values. The transverse mode of the pulse has a M2 of 1.25. Frequency-resolved optical grating and spectral interferometric measurements indicate that the pulse is phase coherent and could be compressed to a few femtoseconds. Furthermore, the multiple-plates approach is shown to be extremely flexible and versatile. It is applicable for a broad range of input powers and materials. The generated continuum is stable and robust. Thus, multiple-plate generated femtosecond continuum could be a promising new light source in ultrafast science and extreme nonlinear optics applications.
159 citations
TL;DR: Damage-free fiber-guidance of milli-Joule energy-level and 600-femtosecond laser pulses into hypocycloid core-contour Kagome hollow-core photonic crystal fibers and free focusing-optics laser-micromachining was demonstrated on different materials.
Abstract: We report on damage-free fiber-guidance of milli-Joule energy-level and 600-femtosecond laser pulses into hypocycloid core-contour Kagome hollow-core photonic crystal fibers. Up to 10 meter-long fibers were used to successfully deliver Yb-laser pulses in robustly single-mode fashion. Different pulse propagation regimes were demonstrated by simply changing the fiber dispersion and gas. Self-compression to ~50 fs, and intensity-level nearing petawatt/cm(2) were achieved. Finally, free focusing-optics laser-micromachining was also demonstrated on different materials.
119 citations
TL;DR: Low-frequency terahertz emission from the ambient air ionized by a two-color femtosecond laser pulse containing a weak additional field tunable near the frequency of the half harmonic is investigated for the first time.
Abstract: We investigate for the first time, both experimentally and theoretically, low-frequency terahertz (THz) emission from the ambient air ionized by a two-color femtosecond laser pulse containing, besides the fundamental-frequency main field, a weak additional field tunable near the frequency of the half harmonic. By controlling the mutual polarization and the powers of the main and additional fields, we determine the dependences of the THz power and polarization on the parameters of the two-color pulse. We also discover the resonantlike dependence of the THz yield on the frequency detuning of the additional field. The analytical formulas obtained using the model of the free-electron residual current density give an excellent agreement with the experimental results.
103 citations
TL;DR: In this article, a novel approach to improve the flatness of wide-band parametric frequency combs is presented, relying on nonlinear pulse shaping prior to parametric mixing in a comb-generating device.
Abstract: A novel approach to improve the flatness of wide-band parametric frequency combs is presented. The method relies on nonlinear pulse shaping prior to parametric mixing in a comb-generating device. The parametric comb is generated in a cavity-less multistage shock-wave mixer, using continuous-wave (CW) laser as comb seed. The pulse shaping is accomplished in a regenerative stage incorporating nonlinear optical/amplifying loop mirror (NOLM/NALM) and provides near-ideal seeds for spectrally equalized frequency comb generation in the output mixing stage. The new technique was implemented separately on two comb generators with a coarse (100 GHz) and dense (10 GHz) tone spacing. A 4 dB flatness over 100 nm is achieved with wide-pitched comb, while the fine-pitched device yielded 1500 tones and possessed sub-2 dB spectral flatness over 120 nm bandwidth.
86 citations
TL;DR: This simple laser system with only one ultrafast laser oscillator and a simple single-pass fiber pulse compressor, generating both high peak power >100 MW and sub-100-fs pulses at megahertz repetition rate, is very interesting for many applications such as high harmonic generation and attosecond science with improved signal-to-noise performance.
Abstract: We present nonlinear pulse compression of a high-power SESAM-modelocked thin-disk laser (TDL) using an Ar-filled hypocycloid-core kagome hollow-core photonic crystal fiber (HC-PCF). The output of the modelocked Yb:YAG TDL with 127 W average power, a pulse repetition rate of 7 MHz, and a pulse duration of 740 fs was spectrally broadened 16-fold while propagating in a kagome HC-PCF containing 13 bar of static argon gas. Subsequent compression tests performed using 8.4% of the full available power resulted in a pulse duration as short as 88 fs using the spectrally broadened output from the fiber. Compressing the full transmitted power through the fiber (118 W) could lead to a compressed output of >100 W of average power and >100 MW of peak power with an average power compression efficiency of 88%. This simple laser system with only one ultrafast laser oscillator and a simple single-pass fiber pulse compressor, generating both high peak power >100 MW and sub-100-fs pulses at megahertz repetition rate, is very interesting for many applications such as high harmonic generation and attosecond science with improved signal-to-noise performance.
86 citations
TL;DR: A laser with a mirror realized by Fano interference between a waveguide and a nanocavity can be modulated at frequencies exceeding 1 THz, not being limited by carrier dynamics as for conventional lasers.
Abstract: We suggest and analyze a laser with a mirror realized by Fano interference between a waveguide and a nanocavity. For small-amplitude modulation of the nanocavity resonance, the laser can be modulated at frequencies exceeding 1 THz, not being limited by carrier dynamics as for conventional lasers. For larger modulation, a transition from pure frequency modulation to the generation of ultrashort pulses is observed. The laser dynamics is analyzed by generalizing the field equation for conventional lasers to account for a dynamical mirror, described by coupled mode theory.
81 citations
TL;DR: This unprecedentedly simple and reliable approach provides reproducible CEP-stabilized pulses in the single-cycle regime for applications such asCEP-sensitive spectroscopy and isolated attosecond pulse generation.
Abstract: We have temporally characterized, dispersion compensated and carrier-envelope phase stabilized 1.4-cycle pulses (3.2 fs) with 160 µJ of energy at 722 nm using a minimal and convenient dispersion-scan setup. The setup is all inline, does not require interferometric beamsplitting, and uses components available in most laser laboratories. Broadband minimization of third-order dispersion using propagation in water enabled reducing the compressed pulse duration from 3.8 to 3.2 fs with the same set of chirped mirrors. Carrier-envelope phase stabilization of the octave-spanning pulses was also performed by the dispersion-scan setup. This unprecedentedly simple and reliable approach provides reproducible CEP-stabilized pulses in the single-cycle regime for applications such as CEP-sensitive spectroscopy and isolated attosecond pulse generation.
78 citations
TL;DR: High-resolution spatiotemporal characterization of an ultrashort pulse is demonstrated, and the sensitivity of the method to spatiotmporal coupling is shown for the case of a pulse with pulse front tilt.
Abstract: We present a method for characterizing ultrashort laser pulses in space and time, based on spatially resolved Fourier transform spectrometry. An unknown pulse is interfered with a delayed, spatially uniform reference on a CCD camera. The reference pulse is created by spatially filtering a portion of the unknown pulse. By scanning the delay between the two pulses, an interferogram is obtained at each pixel, allowing us to determine the spatially resolved phase difference between the unknown pulse and the reference pulse. High-resolution spatiotemporal characterization of an ultrashort pulse is demonstrated, and the sensitivity of the method to spatiotemporal coupling is shown for the case of a pulse with pulse front tilt.
TL;DR: In this paper, the progress of highly functional ultrashort pulse fiber laser sources and their applications are reviewed mainly on the basis of the works of this author, where a passively mode-locked ultra-short pulse-fiber laser using the intensity-dependent absorption element has made great progress using a new type of saturable absorber with a nanocarbon material.
Abstract: Fiber lasers, which consist of ideal waveguides of optical fibers, work as stable, practical, and maintenance-free lasers. A passively mode-locked ultrashort pulse fiber laser using the intensity-dependent absorption element has made great progress using a new type of saturable absorber with a nanocarbon material. The techniques of ultrashort pulse amplification and pulse compression were also developed. Using a combination of specialty fibers, ultrawideband pulse sources, such as wavelength tunable ultrashort pulses and supercontinuum, can be demonstrated. These new light sources are useful for laser applications, especially for optical metrology. In this paper, the progress of highly functional ultrashort pulse fiber laser sources and their applications are reviewed mainly on the basis of the works of this author.
TL;DR: In this paper, a high-energy noiselike rectangular pulse was generated in a mode-locked figure-eight fiber laser, which appeared to have a rectangular shape on the oscilloscope.
Abstract: We report on the generation of a high-energy noiselike rectangular pulse in a mode-locked figure-eight fiber laser. The noiselike pulse appeared to have a rectangular shape on the oscilloscope. The pulse duration increased with increasing pump power, while the peak amplitude remained constant, which is very similar to the pulse evolution of dissipative soliton resonance. However, the pulse type is confirmed as a noiselike pulse using an autocorrelator. With the maximum pump power of 350 mW, the 135 nJ noiselike rectangular pulse with 76 ns duration was achieved. The results provide a new guideline for clarifying an alternative formation mechanism of the high-energy rectangular pulses in fiber lasers.
TL;DR: In this paper, femtosecond double pulses with an inter pulse delay ranging from 100fs up to 2ns are used to study the dynamics of laser ablation of metals under ambient conditions far above the ablation threshold.
TL;DR: By measuring the intensities of 337-nm signal from nitrogen gas mixed with different concentrations of oxygen gas, it is found that oxygen molecules have a significant quenching effect on the nitrogen laser signal.
Abstract: We experimentally demonstrate ultrafast dynamic of generation of the 337-nm nitrogen laser by injecting an external seed pulse into a femtosecond laser filament pumped by a circularly polarized laser pulse. In the pump-probe scheme, it is revealed that the population inversion between the C3Πu and B3Πg states of N2 for the free-space 337-nm laser is firstly built up on the timescale of several picoseconds, followed by a relatively slow decay on the timescale of tens of picoseconds, depending on the nitrogen gas pressure. By measuring the intensities of 337-nm signal from nitrogen gas mixed with different concentrations of oxygen gas, it is also found that oxygen molecules have a significant quenching effect on the nitrogen laser signal. Our experimental observations agree with the picture of electron-impact excitation.
TL;DR: It is proposed that the spectral shape distortions generated by fiber fabrication errors can be significantly attenuated by properly manipulating the pump, and the optimal pump pulse parameters for a given fiber was found.
Abstract: We have numerically investigated the supercontinuum generation and pulse compression in a specially designed all-normal dispersion photonic crystal fiber with a flat-top dispersion curve, pumped by typical pulses from state of the art Ti:Sapphire lasers at 800 nm. The optimal combination of pump pulse parameters for a given fiber was found, which provides a wide octave-spanning spectrum with superb spectral flatness (a drop in spectral intensity of ~1.7 dB). With regard to the pulse compression for these spectra, multiple-cycle pulses (~8 fs) can be obtained with the use of a simple quadratic compressor and nearly single-cycle pulses (3.3 fs) can be obtained with the application of full phase compensation. The impact of pump pulse wavelength-shifting relative to the top of the dispersion curve on the generated SC and pulse compression was also investigated. The optimal pump pulse wavelength range was found to be 750nm<λp<850nm, where the distortions of pulse shape are quite small (< −3.3 dB). The influences of realistic fiber fabrication errors on the SC generation and pulse compression were investigated systematically. We propose that the spectral shape distortions generated by fiber fabrication errors can be significantly attenuated by properly manipulating the pump.
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TL;DR: In this article, a regeneratively and harmonically mode-locked erbium fiber laser was used to generate a coherent Nyquist pulse train at a repetition rate of 40 GHz.
Abstract: Nyquist pulses, which are defined as impulse responses of a Nyquist filter, can be used to simultaneously achieve an ultrahigh data rate and spectral efficiency (SE) Coherent Nyquist optical time-division multiplexing transmission increases SE, but the optical signal-to-noise ratio (OSNR) is limited by the amplitude of the original CW beam To further improve transmission performance, here we describe a new pulsed laser that can emit an optical Nyquist pulse train at a repetition rate of 40 GHz The Nyquist laser is based on a regeneratively and harmonically mode-locked erbium fiber laser that has a special spectral filter to generate a Nyquist pulse as the output pulse The pulse width was approximately 3 ps, and the oscillation wavelength was 155 μm The spectral profile of the Nyquist pulse can be changed by changing the spectral curvature of the filter with a roll-off factor, α, between 0 and 1 A Fabry–Perot etalon was also installed in the laser cavity to select longitudinal modes with a free spectral range of 40 GHz, resulting in the suppression of the mode hopping in the regenerative mode locking A numerical analysis is also presented to explain the generation of a stable Nyquist pulse from the laser The Nyquist laser is important not only for the direct generation of high-OSNR pulses but also for scientific advances, proving that pulse shapes that differ significantly from the conventional hyperbolic-secant and Gaussian pulse shapes can exist stably in a cavity
TL;DR: Experimental examination of two-photon fluorescence excitation at the focus of a spatially chirped femtosecond laser beam reveals an unexpected tilted peak intensity distribution in the focal spot, which can play important roles in applications such as femtosingcond laser micromachining and bio-imaging.
Abstract: We report on experimental examination of two-photon fluorescence excitation (TPFE) at the focus of a spatially chirped femtosecond laser beam, which reveals an unexpected tilted peak intensity distribution in the focal spot. Our theoretical calculation shows that the tilting of the peak intensity distribution originates from the fact that along the optical axis of objective lens, the spatiotemporally focused pulse reaches its shortest duration exactly at the focal plane. However, when moving away from the optical axis along the direction of spatial chirp of the incident pulse, the pulse reaches its shortest duration either before or after the focal plane, depending on whether the pulse duration is measured above or below the optical axis as well as the sign of the spatial chirp. The tilting of the peak intensity distribution in the focal spot of the spatiotemporally focused femtosecond laser beam can play important roles in applications such as femtosecond laser micromachining and bio-imaging.
TL;DR: In this paper, an operation-switchable bidirectional ring-cavity pulsed fiber laser incorporating a carbon-nanotube-based saturable absorber and a polarization-dependent four-port circulator is presented.
Abstract: We present an operation-switchable bidirectional ring-cavity pulsed fiber laser incorporating a carbon-nanotube-based saturable absorber and a polarization-dependent four-port circulator. By manipulating the intra-cavity polarization state of light, two sets of mode-locked pulses in terms of fundamental repetition rate and pulse width can be achieved separately from the same laser cavity. In clockwise direction, the laser generates mode-locked output pulse train with a pulse width of 600 fs and a fundamental repetition rate of 12.68 MHz. While in counter-clockwise direction, the laser generates mode-locked pulses with a pulse width of 480 fs and a fundamental repetition rate of 16.46 MHz. Furthermore, the same laser cavity can produce bidirectional Q-switched output pulse trains with synchronized repetition rate. Such synchronized repetition rate is linearly proportional to pump power. The results show a multi-functional pulsed fiber laser with selectable output pulse trains.
TL;DR: An interferometric method that enables to measure a distance by the intensity measurement using the scanning of the interferometer reference arm and the recording of the interference fringes including the brightest fringe is proposed and it is shown that this method and system can realize absolute distance measurement.
Abstract: We propose an interferometric method that enables to measure a distance by the intensity measurement using the scanning of the interferometer reference arm and the recording of the interference fringes including the brightest fringe. With the consideration of the dispersion and absorption of the pulse laser in a dispersive and absorptive medium, we investigate the cross-correlation function between two femtosecond laser pulses in the time domain. We also introduce the measurement principle. We study the relationship between the position of the brightest fringe and the distance measured, which can contribute to the distance measurement. In the experiments, we measure distances using the method of the intensity detection while the reference arm of Michelson interferometer is scanned and the fringes including the brightest fringe is recorded. Firstly we measure a distance in a range of 10 µm. The experimental results show that the maximum deviation is 45 nm with the method of light intensity detection. Secondly, an interference system using three Michelson interferometers is developed, which combines the methods of light intensity detection and time-of-flight. This system can extend the non-ambiguity range of the method of light intensity detection. We can determine a distance uniquely with a larger non-ambiguity range. It is shown that this method and system can realize absolute distance measurement, and the measurement range is a few micrometers in the vicinity of Nlpp, where N is an integer, and lpp is the pulse-to-pulse length.
TL;DR: In this paper, an optimal control of the output energy of terahertz (THz) waves generated by optical rectification of femtosecond pulses in ZnTe crystals is presented.
Abstract: We report on optimal control of the output energy of terahertz (THz) waves generated by optical rectification of femtosecond pulses in ZnTe crystals. An enhancement by a factor up to 2.4 is obtained with chirped pump pulses. The optimized THz wave also displays a spectral broadening. The influence of the optical pulse shaping on the pump pulse propagation, and consequently on the THz generation efficiency, is numerically investigated and discussed.
TL;DR: The most important feature of the novel pulsed wave is its ability to split into two pulses on passage in a dispersive medium at some critical propagation distance and the subsequent evolution of the split pulses are shown to depend on the source parameters and on the properties of the medium in which the pulse travels.
Abstract: A new class of partially coherent pulses of Schell type with cosine-Gaussian temporal degree of coherence is introduced. Such waves are termed the Cosine-Gaussian Schell-model (CGSM) pulses. The analytic expression for the temporal mutual coherence function of the CGSM pulse in dispersive media is derived and used to study the evolution of its intensity distribution and its temporal degree of coherence. Further, the numerical calculations are performed in order to show the dependence of the intensity profile and the temporal degree of coherence of the CGSM pulse on the incident pulse duration, the initial temporal coherence length, the order-parameter n and the dispersion of the medium. The most important feature of the novel pulsed wave is its ability to split into two pulses on passage in a dispersive medium at some critical propagation distance. Such critical distance and the subsequent evolution of the split pulses are shown to depend on the source parameters and on the properties of the medium in which the pulse travels.
TL;DR: In this paper, a review of the world-wide PW-level femtosecond laser systems are summarized, the output performances of the PULSER-I & II are described, and the future upgrade plan of the multi-PW level is also discussed.
Abstract: The high-power femtosecond laser has now become an excellent scientific tool for the study of not only relativistic laser–matter interactions but also scientific applications. The high-power femtosecond laser depends on the Kerr-lens modelocking (KLM) and chirped-pulse amplification (CPA) technique. An all-Ti:sapphire-based 30-fs PW CPA laser, which is called the PULSER (Petawatt Ultrashort Laser System for Extreme Science Research) has been recently constructed and is being used for accelerating the charged particles (electrons and protons) and generating ultrashort high-energy photon (X-ray and γ-ray) sources. In this review, the world-wide PW-level femtosecond laser systems are first summarized, the output performances of the PULSER-I & II are described, and the future upgrade plan of the PULSER to the multi-PW level is also discussed. Then, several experimental results on particle (electron and proton) acceleration and X-ray generation in the intensity range of mid-1018 W/cm2 to mid-1020 W/cm2 are described. Experimental demonstrations for the newly proposed phenomena and the understanding of physical mechanisms in relativistic and ultrarelativistic regimes are highly expected as increasing the laser peak intensity up to over 1022 W/cm2 ∼1023 W/cm2.
TL;DR: In this article, the authors demonstrate an optical configuration to deliver high-intensity laser pulses with a tilted pulse front for velocity matching over the typical length of a gas jet, where a laser pulse is diffracted from a grating to introduce angular dispersion, and the grating surface is imaged on the target using large demagnification.
Abstract: Recent advances in pulsed electron gun technology have resulted in femtosecond electron pulses becoming available for ultrafast electron diffraction experiments. For experiments investigating chemical dynamics in the gas phase, the resolution is still limited to picosecond time scales due to the velocity mismatch between laser and electron pulses. Tilted laser pulses can be used for velocity matching, but thus far this has not been demonstrated over an extended target in a diffraction setting. We demonstrate an optical configuration to deliver high-intensity laser pulses with a tilted pulse front for velocity matching over the typical length of a gas jet. A laser pulse is diffracted from a grating to introduce angular dispersion, and the grating surface is imaged on the target using large demagnification. The laser pulse duration and tilt angle were measured at and near the image plane using two different techniques: second harmonic cross correlation and an interferometric method. We found that a temporal resolution on the order of 100 fs can be achieved over a range of approximately 1 mm around the image plane.
TL;DR: Depending on the amplitude transfer function of the filter, the possibility of pulse shaping in a passively mode-locked fiber laser by inclusion of a spectral filter into the laser cavity is numerically shown.
Abstract: We numerically show the possibility of pulse shaping in a passively mode-locked fiber laser by inclusion of a spectral filter into the laser cavity. Depending on the amplitude transfer function of the filter, we are able to achieve various regimes of advanced temporal waveform generation, including ones featuring bright and dark parabolic-, flat-top-, triangular- and saw-tooth-profiled pulses. The results demonstrate the strong potential of an in-cavity spectral pulse shaper for controlling the dynamics of mode-locked fiber lasers.
TL;DR: High-frame-rate observations of a single femtosecond laser pulse propagating in transparent medium are demonstrated using the optical polarigraphy technique and an echelon using the single-shot measurements.
Abstract: We have demonstrated high-frame-rate observations of a single femtosecond laser pulse propagating in transparent medium using the optical polarigraphy technique and an echelon. The echelon produced a spatially encoded time delay for the probe pulse to capture directly four successive images of an intense propagating pulse with picosecond time interval and femtosecond time resolution. Using this method, we observed the propagation process of a single femtosecond laser pulse in fused silica. The influence of pulse-energy fluctuation on the spatial and temporal distribution of the single laser pulse was visualized using the single-shot measurements.
TL;DR: In this paper, the authors extend the SWI method using a coarse virtual wave length synthesized by shifting the pulse repetition rate of a mode-locked femtosecond laser, and the proposed concept of NAR extension is experimen-tally verified by measuring a ∼13m distance with repeatability of 9.5 μm.
Abstract: . We revisit the method of synthetic wavelength interferometry (SWI) for absolute measurement of longdistances using the radio-frequency harmonics of the pulse repetition rate of a mode-locked femtosecond laser.Our intention here is to extend the nonambiguity range (NAR) of the SWI method using a coarse virtual wave-length synthesized by shifting the pulse repetition rate. The proposed concept of NAR extension is experimen-tally verified by measuring a ∼13-m distance with repeatability of 9.5 μm (root-mean-square). The measurementprecision is estimated to be 31.2 μm in comparison with an incremental He – Ne laser interferometer. Thisextended SWI method is found to be well suited for long-distance measurements demanded in the fields oflarge-scale precision engineering, geodetic survey, and future space missions. © 2014 Society of Photo-OpticalInstrumentation Engineers (SPIE) [DOI: 10.1117/1.OE.53.12.122403] Keywords: absolute distance measurement; femtosecond laser; synthetic wavelength interferometry.Paper140401SSreceivedMar.10,2014;revisedmanuscriptreceivedApr.8,2014;acceptedforpublicationApr.10,2014;publishedonline May 8, 2014.
TL;DR: The experimental observations of vector pulse trapping and scalar dissipative soliton in a compact nanotube-mode-locked all-fiber laser for the first time to the best knowledge are reported.
Abstract: We report the experimental observations of vector pulse trapping and scalar dissipative soliton in a compact nanotube-mode-locked all-fiber laser for the first time to our best knowledge. The vector pulse exhibits a smooth Gaussian spectral profile without any sidebands. Although two orthogonally polarized components of the vector pulse have different central wavelengths, they copropagate as a unit in the laser cavity with the same speed. The scalar dissipative soliton shows a rectangular spectrum with pulse duration of ~13 ps, and can be compressed to ~320 fs external to the cavity. This flexible laser provides stable, ultrashort vector- and scalar-pulsed sources, which is convenient and attractive for practical applications.
TL;DR: In this paper, a double-clad erbium-ytterbium (EB) ring laser with nonlinear polarization evolution was used for noise-like pulse generation in a km-long fiber ring laser.
Abstract: In this paper, we study noise-like pulse generation in a km-long fibre ring laser including a double-clad erbium?ytterbium fibre and passively mode-locked through nonlinear polarization evolution. Although single noise-like pulsing is only observed at moderate pump power, pulse energies as high as 120?nJ are reached in this regime. For higher pump power, the pulse splits into several noise-like pulses, which then rearrange into a stable and periodic pulse train. Harmonic mode locking from the 2nd to the 48th orders is readily obtained. At pump powers close to the damage threshold of the setup, much denser noise-like pulse trains are demonstrated, reaching harmonic orders beyond 1200 and repetition frequencies in excess of a quarter of a GHz. The mechanisms leading to noise-like pulse breaking and stable high-order harmonic mode locking are discussed.
19 Nov 2014
TL;DR: In this article, the authors demonstrate light pulse combining and pulse compression using a continuous-discrete nonlinear system implemented in a multi-core fiber (MCF) and demonstrate the combining of 77% of the energy into one core with pulse compression over 14× in a 20-core MCF.
Abstract: We demonstrate light pulse combining and pulse compression using a continuous-discrete nonlinear system implemented in a multi-core fiber (MCF). It is shown that the pulses initially injected into all of the cores of a ring MCF are combined by nonlinearity into a small number of cores with simultaneous pulse compression. We demonstrate the combining of 77% of the energy into one core with pulse compression over 14× in a 20-core MCF. We also demonstrate that a suggested scheme is insensitive to the phase perturbations. Nonlinear spatio-temporal pulse manipulation in multi-core fibers can be exploited for various applications, including pulse compression, switching, and combining.