Short-pulse amplification at 745 nm in Ti:sapphire with a continuously tunable regenerative amplifier

We describe the design of a continuously tunable Ti:sapphire regenerative amplifier that is capable of sustaining amplification over a wavelength range from 730 nm to more than 800 nm. The amplifier cavity is tuned with a prism pair in combination with a spherical mirror. It sustains an oscillation bandwidth of 5 nm and produces a chirped output pulse energy of 1.2 mJ compressible to a duration of 140 fs at 745 nm. We present a calculation of the theoretical bandwidth.     

Amplified spontaneous emission in a Ti:sapphire regenerative amplifier

Amplified spontaneous emission power and contrast ratio in a linear miltipass Ti:sapphire regenerative amplifier with a wavelength centered at 1054 nm are calculated and measured. It is shown that the passive losses of a seed pulse and the losses in coupling to the regenerative amplifier cavity mode degrade the intensity contrast ratio to 10(-6)-10(-7). The advantage of an optical parametric chirped pulse amplifier with respect to the contrast ratio is discussed.     

Tunable graphene-based Q-switched erbium-doped fiber laser using fiber Bragg grating

A graphene-based Q-switched erbium-doped fiber laser (EDFL) with a tunable fiber Bragg grating (TFBG) acting as a wavelength tuning mechanism is proposed and demonstrated. The proposed setup utilizes a newly-developed ‘ferrule-to-ferrule transfer’ technique to obtain a single graphene layer that allows for Q-switch operation in the EDFL using a highly doped-gain medium. A TFBG is used as a wavelength tuning mechanism with a tuning range of 10 nm, covering the wavelength range from 1547.66 nm to 1557.66 nm. The system has a wide repetition rate range of over 206.613 kHz from 1.387 kHz to 208.000 kHz with pulse durations of between 94.80 μs to 0.412 μs. The laser output is dependent on the pump power, with energy per pulse of 4.56 nJ to 16.26 nJ. The system is stable, with power and wavelength variations of less than 0.47 dBm and 0.067 nm. The output pulse train is free from self-mode locking and pulse jitters.     

Low-threshold lasing and broad-band multiphoton-excited light emission from Ag aggregate-adsorbate complexes in microcavity

A novel class of composites for optics, microcavities doped with metal fractal aggregates, is studied. Lasing and broad-band Stokes and anti-Stokes emission from (Ag colloidal aggregates)/(adsorbed molecules)/(micro-cavity) composite at low-intensity cw and pulse laser excitation has been found. At 633 nm cw excitation wavelength the emission spectrum contains many peaks, spanning a range from wavelength 200 nm to 800 nm. Experiments with pulse excitation of Ag/dye/microcavity composite show that the duration of the observed broad-band anti-Stokes emission significantly exceeds the pump pulse duration, dye molecule fluorescence time, and relaxation times in silver particles. It may be interpreted as a luminescence governed by long-living triplet states of dye molecules. These observations were made possible by use of a fractal-microcavity composite, where coupling the localized plasmon modes in fractal aggregates with microcavity resonances is provided. The important role of multiphoton resonant transitions between discrete states of a finite-size metal particle in enhanced local fields is shown. Analysis, based on the model of a spherical potential well, shows that the observed spectra contain fingerprints of the quantum size effect.     

Compact efficient eye-safe intracavity optical parametric oscillator with a shared cavity configuration

We present a compact efficient eye-safe intracavity optical parametric oscillator pumped by a passively Q-switched Nd:YAG laser in a shared cavity configuration. A signal pulse of 3.3 mJ energy at a 1573 nm wavelength with a peak power of 150 kW was achieved. The effective conversion efficiency with respective to the optimized 1064 nm Q-switched pulse energy was as high as 51%.     

Wideband tunable Q-switched fiber laser using graphene as a saturable absorber

An ultra-wide wavelength tuning range, which covers three different band regions consisting of the S-, C-, and L-bands, is proposed and demonstrated for a graphene-based Q-switched erbium-doped fiber laser using a tunable bandpass filter as the wavelength tuning and filtering mechanism. A 3?m length of erbium-doped fiber is used as the gain medium in a ring laser cavity configuration, with absorption coefficients of between 11 and 13 dB?m^?1 at 980?nm and about 18?dB?m^?1 at 1550?nm. The tuning range of the Q-switching pulses covers a wide wavelength range of 58?nm, which spans from 1512.5?nm to 1570.5?nm. In addition, the lasing and Q-switching thresholds are considerably low, with respective values of ～11.0?mW and ～18.4?mW. A repetition rate of 55.3?kHz is obtained at the maximum pump power of 100.4?mW, together with pulse width and pulse energy of 1.6?μs and 25.8?nJ, respectively.     

Study of the reflectance of an aluminum film under simultaneous action of current pulses and laser radiation

We have experimentally observed a reversible increase in the reflectance of aluminum at a wavelength of 308 nm during the passage of an electric current pulse with a density of up to 100 MA/cm². It is suggested that the effect is explained by partial reflection of the incident radiation by free electrons injected into the conduction band of an oxide film on the metal surface during the passage of a current pulse.     

Short-pulse Injection-locking of a Mercury Chloride Laser

Abstract

We report the injection locking of a mercury chloride discharge laser. This has been achieved using an injection pulse much shorter than the slave pulse duration. Selective enhancement of HgCl laser output at wavelengths to the blue of the usual 558 nm lasing region has been observed. Mercury metastables, produced in the discharge, are found to have an absorption line coincident with an HgCl gain peak at 547 nm, and laser action at this wavelength is inhibited. This absorption has been counteracted by correctly timing the entry of the injected pulse into the slave laser cavity.     

Ultra-high-speed phase-sensitive optical coherence reflectometer with a stretched pulse supercontinuum source

We demonstrate an ultra-high-speed phase-sensitive time-wavelength-domain optical coherence reflectometer with a stretched pulse supercontinuum source. A pulsed fiber laser operating at 10 MHz repetition rate was used to generate a pulsed supercontinuum of 30 ps pulse duration by using a nonlinear optical fiber. The supercontinuum pulses are stretched into 70 ns pulses with a highly dispersive fiber. With this stretched pulse source, we have built a phase-sensitive optical coherence reflectometer that measures the spectral interferogram of reflected light. By using the linear relation between the wavelength and the temporal position in a linearly chirped pulse, ultra-high-speed spectrum measurement can be obtained with this method in the time domain. We have demonstrated ultra-high-speed two-dimensional surface profiling for a standard image target and high-speed single-point monitoring for a fixed point under vibrational motion. It is shown that the measurement speed for the position of a single point can be as fast as 2.5 MHz, while the position accuracy can be better than 4.49 nm.     

Infrared-ultraviolet sum-frequency generation spectrometer with a wide tunability of the ultraviolet probe

We have constructed a multiplex infrared-ultraviolet (IR-UV) sum-frequency generation (SFG) spectrometer that has a wide tunable range (235-390 nm) of the UV probe wavelength. The tunable UV probe was obtained by doubling the signal output of an optical parametric amplifier pumped by a 400 nm picosecond pulse. A prism monochromator was used as a tunable sharp-cut bandpass filter to reduce stray light due to the scattering of the UV probe so that any wavelength within the tunable range can be chosen as that of the UV probe. The SFG spectra of p-mercaptobenzoic acid on a gold substrate was measured with 289 and 334 nm UV probes. The SFG vibrational band intensities due to the carbonyl stretch mode and a phenyl ring stretch mode measured with the 289 nm probe were approximately three times larger than those measured with the 334 nm probe. The enhancement was ascribed to an electronic resonant effect.     

Investigation of damage threshold to TiO2 coatings at different laser wavelength and pulse duration

Laser-induced damages to TiO₂ single layers and TiO₂/SiO₂ high reflectors at laser wavelength of 1064 nm, 800 nm, 532 nm, and pulse width of 12 ns, 220 ps, 50 fs, 8 ns are investigated. All films are prepared by electron beam evaporation. The relations among microstructure, chemical composition, optical properties and laser-induced damage threshold (LIDT), have been researched. The dependence of damage mechanism on laser wavelength and pulse width is discussed. It is found that from 1064 nm to 532 nm, LIDT is mainly absorption related, which is determined by film's extinction coefficient and stoichiometric defects. The rapid decrease of LIDT at 800 nm is due to the pulse width factor. TiO₂ coatings are mainly thermally by damaged at long pulse (τ ≥ 220 ps). The damage shows ablation feature at 50 fs.     

Operation of a Ti:sapphire laser pumped by a 499-nm green laser

We report, for the first time, to our knowledge, the operation of a tunable Ti:sapphire laser pumped by a third-order Raman XeCl-H(2) laser system at 499 nm with a 60-ns pulse duration. The slope efficiency is 59% for this laser, producing pulses of 20-ns duration. The highest conversion-energy efficiency obtained is 41%, with an output energy of 1.2 mJ. The tuning range for a single set of cavity mirrors is 680-834 nm and is limited mainly by the mirror reflectivity. This study shows that a combined laser system based on a XeCl excimer laser can offer wavelength diversity.     

All-fiber quasi-continuous wave supercontinuum generation in single-mode high-nonlinear fiber pumped by submicrosecond pulse with low peak power

We demonstrate quasi-continuous wave supercontinuum generation in a single-mode high-nonlinear fiber (HNLF) in 1.55 μm band, which is pumped by the amplified passively Q-switched submicrosecond pulse. The pump wavelength is in the normal dispersion region of HNLF and near to the zero-dispersion wavelength. The broad SC spectral range from 1200 to 2260 nm is obtained with the low pump peak power of 17.8 W. The 20 dB bandwidth of 922 nm from 1285 to 2207 nm is obtained with the assumption that the peak near 1560 nm is filtered. The spectrum density for the 20 dB bandwidth is from -27.5 to -7.5 dbm/nm.     

All-optical switching in Pharaonis phoborhodopsin protein molecules

Low-power all-optical switching with pharaonis phoborhodopsin (ppR) protein is demonstrated based on nonlinear excited-state absorption at different wavelengths. A modulating pulsed 532-nm laser beam is shown to switch the transmission of a continuous-wave signal light beam at: 1) 390 nm; 2) 500 nm; 3) 560 nm; and 4) 600 nm, respectively. Simulations based on the rate equation approach considering all seven states in the ppR photocycle are in good agreement with experimental results. It is shown that the switching characteristics at 560 and 600 nm, respectively, can exhibit negative to positive switching. The switching characteristics at 500 nm can be inverted by increasing the signal beam intensity. The profile of switched signal beam is also sensitive to the modulating pulse frequency and signal beam intensity and wavelength. The switching characteristics are also shown to be sensitive to the lifetimes of$mmb pbf pR_bf M$and$mmb pbf pR_bf O$intermediates. The results show the applicability of ppR as a low-power wavelength tunable all-optical switch.     

Picosecond-pulse wavelength conversion based on cascaded second-harmonic generation-difference frequency generation in a periodically poled lithium niobate waveguide

The wavelength conversion of picosecond optical pulses based on the cascaded second-harmonic generation-difference-frequency generation process in a MgO-doped periodically poled lithium niobate waveguide is studied both experimentally and theoretically. In the experiments, the picosecond pulses are generated from a 40 GHz mode-locked fiber laser and two tunable filters, with which the lasing wavelength can be tuned from 1530 to 1570 nm, and the pulse width can be tuned from 2 to 7 ps. New-frequency pulses, i.e., converted pulses, are generated when the picosecond pulse train and a cw wave interact in the waveguide. The conversion characteristics are systematically investigated when the pulsed and cw waves are alternatively taken as the pump at the quasi-phase-matching wavelength of the device. In particular, the conversion dependences on input pulse width, average power, and pump wavelength are examined quantitatively. Based on the temporal and spectral characteristics of wavelength conversion, a comprehensive analysis on conversion efficiency is presented. The simulation results are in good agreement with the measured data.     

Multiwavelength picosecond and single wavelength femtosecond pulses emission in a passively mode-locked fiber laser using a semiconductor saturable absorber mirror and a contrast ratio tunable comb filter

We propose and demonstrate a highly flexible fiber laser capable of generating stable multiwavelength picosecond and single wavelength femtosecond pulses by using a semiconductor saturable absorber mirror and a contrast ratio tunable comb filter. In the multiwavelength lasing regime, up to 11-wavelength stable mode-locked pulses in 3 dB bandwidth with a channel spacing of 0.8 nm were obtained. While in the single wavelength with broadband spectrum lasing regime, the fiber laser emitted 576 fs soliton pulse. Through changing the contrast ratio of the comb filter, the conversion between the multiwavelength picosecond and single wavelength femtosecond pulsed operations could be efficiently achieved.     

The effect of laser radiation on the conductivity of poly(diacetylene)

It is demonstrated that an increase in the dark conductivity of poly(diacetylene) (PDA) upon laser irradiation in oxygen-containing media is determined by the formation of thin conducting surface layers. Pulsed laser irradiation at an energy of 0.04 J, a wavelength of 530 nm, and a pulse duration of 20 ns increases the conductivity of the surface PDA layers by four orders of magnitude. It is supposed that the laser-induced degradation and the subsequent stabilization of the surface PDA layers are mainly determined by photooxidation.     

Digital programmable light spectrum synthesis system using a digital micromirror device

We present a digital programmable light spectrum synthesis system based on a digital micromirror device (DMD) from Texas Instruments. A DMD pattern-scanning calibration method is developed and applied to the synthesis of various infrared C-band (1530-1565 nm) spectral profiles, including a fast programmable tunable light source with a bandwidth of approximately 3.8 nm, a square profile, a sawtooth waveform, and a triangular spectrum profile. The experimental results show that the wavelength resolution of the DMD spectrum synthesis system is approximately 0.076 nm/pixel. The proposed spectrum synthesis system has a number of key advantages, including a rapid and stable performance and multichannel compatibility. The spectrum synthesis system is suitable for various applications, including pulse shaping for coherent control and harmonic generation, a tunable light source, an equalizer for erbium-doped fiber amplifiers, and a wavelength scanner.     

高强度超短脉冲单块BBO晶体的三倍频研究

对高强度超短脉冲单块BBO晶体产生三倍频的过程进行了理论及实验研究.定量分析入射基频光强度、晶体厚度、晶体失谐角和方位角等因素对三倍频光转换效率和时间波形的影响,并对实验参数进行了优化.针对脉冲宽度100 fs、带宽25nm、中心波长810 nm、能量为6 mJ左右的超短脉冲基频光,采用单块BBO晶体开展了三倍频实验研究,获得了0.8%的三倍频转换效率,并对实验结果进行了分析.在此基础上,进一步提出了提高单块BBO晶体超短脉冲三倍频转换效率的改进措施.     

脉冲激光模拟器

介绍了一种用于测试激光测距机系统性能的脉冲激光模拟器。该模拟器由１０６４ｎｍ半导体浙江器、准直光学系统、驱动电路、同步及延迟电路、仿真计算软件等组成,可以模拟脉冲激光测距机在各种大气条件下,对不同距离及不同特性的目标测距时的回波信号。