Atmospheric Gas Detection with Broadband Sources

We investigate a new experimental method for detecting molecules from the ultraviolet to the near infrared range using ultrashort laser pulses. Two types of sources are used: a white light continuum generated by 200khz Ti: Sapphire regenerative amplifier system, and a near-gaussian femtosecond pulse (100 fs) generated by an optical parametric amplifier and tunable from 0.45 to 2.4 m. Up to now, this technique has only been performed in the visible domain. Both broadband sources allow the detection of the oxygen and the water vapor bands. Moreover, a new extraction method has been implemented, which provides the molecules' concentration by using a nonlinear fit technique.     

全固态kHz啁啾脉冲飞秒激光放大器

要建造大功率超强激光系统,必须将nJ量级的种子进行放大,以得到mJ量级以及更高能量的激光输出.为达到这个目的,必须使种子能量指数增加,再生腔放大器是实现这一目的的良好途径;同时,为了得到更稳定的激光输出,须采用高重复频率的泵浦源.为此,设计了一种kHz重复频率激光泵浦的再生放大器,使用15 mJ的527 nm的绿光泵浦,得到了约2.3 mJ的800 nm放大激光输出,同时,对其输出激光的光谱特性进行了测量,将带宽为40 nm的种子注入后,得到了光谱带宽约为30 nm激光输出.     

Two-color two-photon excitation of indole using a femtosecond laser regenerative amplifier

The fluorescence emission from indole resulting from two-color two-photon (2C2P) excitation with 400 and 800 nm wavelengths is observed, using the second harmonic and fundamental wavelength of a 800 nm 40 fs pulsed Ti:Sapphire femtosecond (fs) regenerative amplifier operating at a repetition rate of 1 kHz. By delaying one fs laser pulse relative to the other, the cross correlation of fluorescence is observed, which indicates the generation of 2C2P fluorescence signal in the experiment. The strongest 2C2P fluorescence emission characterized by the peak of cross correlation curve suggests optimal temporal overlap of the two fs laser pulses. The 2C2P fluorescence signal is linearly dependent on the total excitation intensity. The fluorescence signals with 400 nm and 800 nm irradiation alone are also demonstrated and discussed in this paper.     

175 to 210 nm widely tunable deep-ultraviolet light generation based on KBBF crystal

We have developed a widely tunable deep-ultraviolet (DUV) laser in the wavelength range from 175 to 210 nm by the fourth harmonic generation of Ti:Sapphire laser. The fourth harmonic generation is performed by direct second-harmonic generation (SHG) of a frequency doubled Ti:Sapphire laser with KBBF crystal. The highest output power is 2.23 mW at 193 nm, and the power of the DUV laser is more than 1 mW from 182 nm to 210 nm. To our knowledge, it is the first demonstration of milliwatt-level widely tunable DUV all-solid-state laser below 200 nm by direct SHG technique.     

Spectral shaping filter for broadband amplifiers

We present the design and implementation of a high-damage threshold spectral shaping filter that can be used to counteract gain narrowing in broadband laser amplifier systems. In contrast to earlier approaches to this problem, the filter has a wide range of tunability in both reflectivity and center wavelength. The shape of the reflectivity curve enables the production of an apodized output spectrum with a clean transform limit. We demonstrate the use of this filter in both regenerative and multipass Ti:Sapphire amplifier systems, yielding super-Gaussian amplified spectra of 70-80 nm width.     

无展宽器的高重复率钛宝石啁啾飞秒脉冲再生放大器的研究

通过优化放大腔结构参数和采用高光束质量的泵浦激光,依靠放大器腔内各个元件的色散展宽种子脉冲, 用钛宝石作为增益介质, 在低泵浦能量下, 实现了高光束质量,高稳定的中等能量的高重复率飞秒脉冲再生放大. 将钛宝石晶体离焦放置,有效的避免了光学损伤. 在1.1 mJ的绿光泵浦下, 获得了2 ps, 120 μJ, 重复频率为1 KHz, 光谱带宽7.8 nm的放大脉冲, 用石英棱镜对压缩可得到130 fs的激光脉冲.     

Tunable no-tracking OPO-OPA tandem in the near-infrared pumped by a Ti:Sapphire laser

We report the performance of a type-II KTP optical parametric oscillator-amplifier tandem pumped in a non-critical phase-matching configuration by a flashlamp-pumped Ti:Sapphire laser, scanned from 730 to 900 nm. Tunable signal and idler wavelengths are generated from 1.065 to 1.290 µm and from 2.320 to 2.970 µm, respectively, without crystal tracking. Slope efficiency is as high as 32% for the signal conversion only. A KNbO₃ crystal has also been tested as a parametric amplifier in a no-tracking configuration and yields comparable gain.     

Seven-terawatt Ti:sapphire laser system operating at 50 Hz with high beam quality for laser Compton femtosecond X-ray generation

We present a 7-TW Ti:sapphire laser system operating at 50 Hz for laser Compton femtosecond X-ray generation. This laser system delivers 8.4 W of average output power at a repetition rate of 50 Hz with a pulse width of 24 fs. It demonstrates successful management using a dynamically stable resonator in the regenerative amplifier and compensation for thermal lensing by a convex mirror in a ring-type four-pass power amplifier. We also present the results of closed-loop corrections for distorted wavefronts of amplified and compressed laser pulses, using an adaptive optical system consisting of a Shack–Hartmann-type wavefront sensor and a deformable mirror. This closed-loop correction results in dramatic improvements, reducing wavefront distortions below 0.05 λ rms. Received: 31 October 2002 / Revised version: 3 March 2003 / Published online: 5 May 2003 RID="*" ID="*"Corresponding author. Fax: +81-298/61-3349, E-mail: ito@festa.or.jp     

A compact Ti:sapphire femtosecond pulse amplifier without stretcher at high repetition rate

We report a simple approach to amplify Ti:sapphire femtosecond pulses to moderate energy levels by achirped regenerative amplifier. The seed pulses are broaden naturally because of the material dispersionof system components in regenerative cavity. The off-focusing Ti:sapphire crystal avoids effectively theoptical damage. It sustains amplification over a wavelength range from 775 nm to more than 810 nmwith a birefringent filter and an oscillation bandwidth of 7.7 nm, and produces 2.1 ps chirped outputpulse energy of 100μJ at 1.1-mJ pumping energy. This system shows good performances in stability andefficiency with the benefits of two thin-film polarizers and TEM00 mode pumping laser.     

Performance study of a soft X-ray harmonic generation FEL seeded with an EUV laser pulse

The performance of a free electron laser (FEL) using a low-power extreme ultraviolet (EUV) pulse as an input seed is investigated. The parameters are appropriate for 30 nm seeds produced from high-power Ti:Sapphire pulses using high harmonic generation schemes. It is found that, for reasonable beam parameters, robust FEL performance can be obtained. Both time-independent and time-dependent simulations are performed for varying system parameters using the GENESIS simulation code. A comparison is made with a two-stage harmonic FEL that is seeded by a high-power Ti:Sapphire pulse.     

High energy femtosecond supercontinuum light generation in large mode area photonic crystal fiber

A large mode area photonic crystal fiber (LMA PCF) with an effective area of 180 μm² is used to generate a high energy, micro-joule range, flat, octave spanning supercontinuum (SC) extending from ~ 600 nm to ~ 1720 nm. A train of femtosecond pulses from a widely-tunable parametric amplifier pumped by a Ti:Sapphire regenerative amplifier system are coupled into a 20 cm length of LMA PCF generating a SC of 1.4 μJ energy. We present an experimental study of the high energy SC as a function of the input power and the pumping wavelength. The spectrum obtained at a pump wavelength of 1260 nm presents spectral flatness variation less than 12 dB over more than 1.1 octave bandwidth. The physical processes behind the SC formation are described in the normal and the anomalous dispersion regions. Our experimental results are successfully compared with the numerical solution of the nonlinear Schrödinger equation.     

Femtosecond laser source for real-time atmospheric gas sensing in the UV–visible

We propose an experimental method for detecting molecules in the UV–visible range using ultrashort laser pulses. Two types of sources are used: a continuum generated by 200 kHz Ti:sapphire regenerative amplifier system extending from 320 to 1100 nm, and a near-gaussian femtosecond pulse (100 fs) generated by an optical parametric amplifier. Both broadband sources allow the real-time detection of the oxygen, the nitrogen dioxide NO₂ and the water vapor bands. Moreover, the concentration of NO₂ can be determined within the 10 ppb sensitivity range by using a specific nonlinear fit technique.     

An Ultra-Broadband Spatially Dispersed Regenerative Amplifier Free from Spatial Chirp

An ultra-broadband Ti：sapphire regenerative amplifier based on spatially dispersed amplification is demonstrated experimentally. Departing from previous reports, a new design of the cavity gets the amplified pulse free from spatial chirp. Utilizing this new regenerative amplifier, chirped pulses with bandwidth （FWHM） of about 80 nm are obtained, and the bandwidth is limited only by that of the incident seed pulses.     

TW级Ti：Al2O3飞秒激光放大器

报道ＴＷ（１０＾１２Ｗ）级Ｔｉ：Ａｌ２Ｏ３飞秒激光放大器的研究，采用Ｔｉ：Ａｌ２Ｏ３自锁模激光振荡器和脉冲啁啾放大技术，获得了能量为８４ｍＪ，脉宽为７５ｆｓ的放大光脉冲，峰值功率达到ＴＷ量级。     

Narrowband solid state vuv coherent source for laser cooling of antihydrogen

We describe the design and performance of a solid-state pulsed source of narrowband (< 100 MHz) Lyman-α radiation designed for the purpose of laser cooling magnetically trapped antihydrogen. Our source utilizes an injection seeded Ti:Sapphire amplifier cavity to generate intense radiation at 729.4 nm, which is then sent through a frequency doubling stage and a frequency tripling stage to generate 121.56 nm light. Although the pulse energy at 121.56 nm is currently limited to 12 nJ with a repetition rate of 10 Hz, we expect to obtain greater than 0.1 μJ per pulse at 10 Hz by further optimizing the alignment of the pulse amplifier and the efficiency of the frequency tripling stage. Such a power will be sufficient for cooling a trapped antihydrogen atom from 500 mK to 20mK.     

Two-color chirped-pulse amplification in an ultrabroadband Ti:sapphire ring regenerative amplifier

We have developed a high-energy, ultrabroadband Ti:sapphire ring regenerative amplifier capable of producing in excess of 20-mJ output at a 10-Hz repetition rate. The technique of chirped-pulse amplification is used to generate two-color, time-synchronized pulses with central wavelength separations of up to approximately 120 nm and with a total energy of 10 mJ by use of a regenerative pulse-shaping technique. Mid-infrared pulses tunable from 6 to 11 microm are generated by difference frequency mixing the two-color outputs.     

输出能量4mJ的1kHz飞秒掺钛蓝宝石激光再生放大研究

针对高能量千赫兹重复频率飞秒激光的应用需求,设计了一套采用线性再生腔结构的高效率飞秒钛宝石激光啁啾脉冲放大系统.通过优化腔型设计,在重复频率为1 kHz、单脉冲能量为20 mJ的527 nm激光抽运下,将展宽后的800 nm啁啾脉冲激光的能量放大到5.8 mJ,对应斜效率达到30.7%.进一步通过色散补偿压缩脉冲宽度,获得了单脉冲能量为4 mJ、脉冲宽度为45.7 fs的输出,稳定性测量表明激光的能量抖动仅为0.18%(均方根值).     

Study on the three-photon properties of a triphenylamine derivative with three conjugated branches

Three-photon pumped frequency-upconversion fluorescence and nonlinear transmission properties of tris-[4-(2-{4-[5-(4-tert-butyl-phenyl)-[1,3,4]oxadiazol-2-yl]-phenyl}-vinyl)-phenyl]-amine (TPAD3) are studied using a Ti:Sapphire oscillator–amplifier system associated with an optical-parametric amplifier, which could specifically provide ～80 fs duration and 1175–1300 nm laser pulses for three-photon excitation. The dye shows very efficient three-photon pumped frequency-upconversion fluorescence and three-photon absorption at wavelengths from 1175 nm to 1300 nm. In our study, the beam intensity distribution is also taken into account. For the first time we give the analytical solution to nonlinear transmission of a three-photon absorption process when the incident beam has a Gaussian transverse spatial profile.     

Generation of high average power, 7.5-fs blue pulses at 5 kHz by adaptive phase control

The spectral width of a 5-kHz Ti:sapphire laser system was broadened by spectral control in a regenerative amplifier consisting of broadband chirped mirrors. The dispersion over the wide spectral range was compensated by a deformable mirror along with a genetic algorithm, resulting in a pulse width of 15 fs. The pulse width is the shortest, to our knowledge, in chirped pulse amplification systems with a regenerative amplifier. The phase distortion of broadband frequency doubling in addition to the Ti:sapphire laser was compensated by using the self-diffraction intensity in sapphire as the feedback signal into the genetic algorithm, resulting in a pulse width of 7.5 fs. The average power of the second harmonic was 1 W with a fundamental input of 7 W.     

钛宝石泵浦的Yb:YAG晶体的激光性能

测量了Yb:YAG晶体的光谱特性,用Ar⁺离子泵浦钛宝石激光器作为泵浦源泵浦Yb:YAG晶体,采用平平腔设计,当输出耦合镜T_1.053μm=4.26%,泵浦功率为1410mW时,得到320mW1.053μm的高效CW激光输出,斜率效率为54%,外推阈值功率为203mW。