基于单个BBO晶体载波包络相位稳定的高效率光参量放大器

基于单个BBO非线性晶体,利用非共线光参量放大技术,研究了载波包络相位稳定的高效率可调谐近红外脉冲产生.以载波包络相位稳定的飞秒激光放大系统产生的白光作为种子光,注入一个二类匹配的二级光参量放大器,在1350 nm波段获得抽运-信号光34%的转换效率.利用f—2f光谱相干测量技术,放大脉冲载波包络相位的抖动30 min内小于137 mrad.该方法提供了一种简单高效的载波包络相位稳定的红外脉冲产生技术.     

飞秒光参量放大中三波群速失配的补偿

为了消除群速失配对参量放大的不利影响，描述了利用脉冲波面倾斜与非共线相位匹配相结 合，完全补偿飞秒光参量放大（OPA）中三波群速失配的新方法.计算了在BBOⅠ类、Ⅱ类相 位匹配条件下， 三波实现群速匹配时，相位匹配角、脉冲波面倾斜角以及非共线角随信号 光波长的变化.并分析了三波群速匹配对空间走离长度、参量增益和参量带宽的影响.结果表 明，在BBOⅠ类、Ⅱ类相位匹配条件下，利用该方法均能实现飞秒OPA连续调谐时三波的群速 匹配，从而大大增加了三波的有效互作用长度，为能够获得高增益，窄脉宽的参量光脉冲提 供了理论依据和指导. 关键词： 群速匹配 脉冲波面倾斜 非共线相位匹配 飞秒光参量放大     

Acousto-optical shaping of ultraviolet femtosecond pulses

This work demonstrates a simple method for ultraviolet (UV) acousto-optical pulse shaping of both spectral amplitude and phase. A fused-silica acousto-optical modulator is used to ensure high transmission and a high damage threshold at 400-nm center wavelength. The technique eliminates complications associated with the parametric transfer of the spectral phase of near-infrared pulses through a nonlinear process out to UV wavelengths, by separating the frequency doubling and shaping processes. Three illustrative applications of phase control are presented: the compensation of material dispersion, the generation of multiple pulse trains, and the generation of arbitrarily shaped pulse trains. Self-diffraction frequency-resolved optical gating is used to characterize the success of the technique.     

Frequency doubling and Fourier domain shaping the output of a femtosecond optical parametric amplifier: easy access to tuneable femtosecond pulse shapes in the deep ultraviolet

Tuneable, shaped, ultraviolet (UV) femtosecond laser pulses are produced by shaping and frequency doubling the output of a commercial optical parametric amplifier (OPA). A reflective mode, folded, pulse shaping assembly employing a spatial light modulator (SLM) shapes femtosecond pulses in the visible region of the spectrum. The shaped visible light pulses are frequency doubled to generate phase- and amplitude-shaped, ultrashort light pulses in the deep ultraviolet. This approach benefits from a simple experimental setup and the potential for tuning the central frequency of the shaped ultraviolet waveform. A number of pulse shapes have been synthesised and characterised using cross-correlation frequency resolved optical gating (XFROG). This pulse shaping method can be employed for coherent control experiments in the ultraviolet region of the spectrum where many organic molecules have strong absorption bands. D.S.N. Parker and A.D.G. Nunn contributed equally to this work.     

All-optical control of the carrier-envelope phase with multi-stage optical parametric amplifiers verified with spectral interference

Intense ultrashort laser pulses with stabilized carrier-envelope phase (CEP) are generated at 800 nm by using multi-stage collinear and non-collinear optical parametric amplifiers (OPAs). The first-stage collinear OPA is directly pumped by the fundamental-wave pulses and tuned to generate idler pulses at 1600 nm, which are further amplified by a second-stage collinear OPA, and then frequency-doubled to generate CEP-stabilized pulses at 800 nm. A non-collinear OPA is used to amplify the CEP-stabilized pulses at 800 nm. The combination of different OPAs can generate and amplify CEP-stabilized pulses at 800 nm without any detrimental influence from the fundamental-wave pulses. The CEP stabilization is verified with a simple and robust spectral interference setup. The stable interference pattern is measured for every single pulse and compared with the unstable pattern from pulses of random CEP. PACS 42.65.Re; 42.65.Yj; 42.25.Kb     

KBe2BO3F2飞秒光参量放大中的群速匹配

提出了KBe₂BO₃F₂ （KBBF）飞秒光参量放大中三波群速完全匹配的方法.对于Ⅰ类相位匹配方式采用非共线结构及倾斜抽运光脉冲波面,对于Ⅱ类相位匹配方式采用共线结构同时倾斜抽运光和信号光脉冲波面,可实现参量带宽最大时三波群速的完全匹配,从而获得更高增益,更窄脉宽的参量光. 关键词： 群速匹配 相位匹配 脉冲波面倾斜 飞秒光参量放大     

Carrier-envelope phase offset for pulses from a tunable optical parametric amplifier

The carrier-envelope phase (CEP) characteristics of the tunable infrared laser pulses from a noncollinear optical parametric amplifier (OPA) with passively stabilized CEP are investigated experimentally. We compare the CEP fluctuation of different wavelength outputs from the OPA which is seeded by the idler pulse of a difference frequency generation (DFG) process. It is found that when the OPA output is tuned to a longer wavelength, the CEP fluctuation becomes less sensitive to the jitter of laser intensity and the phase mismatch, and therefore more stable CEP for the longer wavelength output pulses is realized.     

Numerical study on pulse contrast enhancement in a short-pulse-pumped optical parametric amplifier

We investigate pulse cleaning behaviors in short-pulse-pumped optical parametric amplifiers (OPA). We theoretically study the contrast enhancement of amplified signal pulse and generated idler pulse, and reveal their dependence on the parametric gain in both the regimes of small signal and saturated amplifications. The signal contrast enhancement is nearly equal to the parametric gain, while the idler contrast is approximately equal to the product of the contrasts of the pump and signal pulses in a low gain OPA and increases with the gain. The effects of group-velocity mismatch and group-velocity dispersion on the contrast enhancement are also investigated. The results presented in this paper are of value for pulse cleaning.     

A double-pass optical parametric amplifier seeded by a blue-shifted output of a photonic-crystal fiber

A blue-shifted output of a photonic-crystal fiber, providing a frequency upconversion of femtosecond Ti:sapphire laser pulses, is used to seed a double-pass optical parametric oscillator (OPA). The OPA is based on a BBO crystal, pumped by 65-mW 150-fs second-harmonic pulses of a Ti:sapphire laser. Gain factors in excess of 10³ are demonstrated for such an OPA, yielding tunable light pulses within the range of wavelengths from 420 to 650 nm, a peak power up to 250 kW, and a typical pulse width of about 200 fs at a repetition rate of 100 kHz. PACS 42.81.Gs; 42.81.Qb     

Controlled shaping of ultrafast electric field transients in the mid-infrared spectral range

We experimentally demonstrate amplitude and phase shaping of femtosecond mid-infrared pulses in a range centered about 14 mum . Single pulses with a tailored optical phase and phase-locked double pulses are generated by phase-matched difference-frequency mixing in a GaSe crystal of near-infrared pulses shaped with a liquid-crystal modulator. The electric field transients are directly measured by free-space electro-optic sampling, yielding pulse durations of 200-300 fs. Our data are in good agreement with a model that describes phase-matched optical rectification.     

Group-velocity-dispersion-compensated femtosecond optical parametric amplifier

A tilted pulse front geometry is known to allow group-velocity-dispersion (GVD) compensated propagation of short pulses of different wavelengths in dispersive media. This scheme is shown to be applicable to an optical parametric amplifier (OPA) pumped at 450nm. A numerical calculation shows that a certain combination of the tilt of the pulse front and the angle between the interacting beams provides optimum GVD compensation for each wavelength. The parameters providing broadband tunability are identified. The tunability of the GVD-compensated OPA pumped with 55fs pulses was experimentally demonstrated between 545nm and 645nm. This revised version was published online in November 2006 with corrections to the Cover Date.     

Energy-scalable pulsed mid-IR source using orientation-patterned GaAs

Coherent mid-IR sources based on orientation-patterned GaAs (OPGaAs) are of significant interest in diverse scientific, medical, and military applications. The generation of long-wavelength mid-IR beams in OPGaAs using optical parametric oscillation exhibits limitations in the obtainable pulse energy and peak power. The master oscillator power amplifier concept is demonstrated in OPGaAs, by which a mid-IR source based on optical parametric oscillation can be scaled to high energy by amplification of the output of the optical parametric oscillator in an optical parametric amplifier (OPA). A fivefold increase in the pulse energy is obtained using this method by amplifying 3.85μm pulses in an OPGaAs OPA pumped by a Th,Ho:YLF Q-switched laser.     

Optical parametric chirped pulse amplification based on photonic crystal fibre

A compact two-stage optical parametric chirped pulse amplifier based on photonic crystal fibre is demonstrated.A 1064-nm soliton pulse is obtained in a home-made photonic crystal fibre (PCF) with femtosecond pulse pumping and then amplified to 2 mJ in an Nd:YAG regenerative amplifier.After the amplified pulses pass through the LBO crystal,the 532-nm double-frequency light with an energy of 0.8 mJ and a duration of over 100 ps at 10-Hz repetition rate is generated as a pump source in the following two-stage optical parametric amplification (OPA).The 850-nm chirped signal light gain from the stretcher is 1.5×10 4 in the first-stage OPA while it is 120 in the second-stage OPA.The total signal gain of optical parametric chirped pulse amplification (OPCPA) can reach 1.8×10 6.     

Frontend light source for short-pulse pumped OPCPA system

We present the development of a light source for generating optically synchronized seed pulses both for the parametric amplifier chain and the pump-laser chain of the Petawatt Field Synthesizer (PFS), which is currently under construction at MPQ. The PFS system aims at delivering waveform-controlled few-cycle laser pulses with PW-scale peak power using optical parametric chirped pulse amplification (OPCPA). Methods of generating the broadband near-infrared (NIR) seed pulses for the OPCPA chain by spectral broadening using few-cycle pulses are presented. We also demonstrate the generation of a supercontinuum spanning up to three octaves (270–1500 nm) using cascaded hollow-core fibers which supports sub-cycle pulse duration.     

Advanced time-resolved absorption spectroscopy with an ultrashort visible/near IR laser and a multi-channel lock-in detector

Ultrashort visible-near infrared (NIR) pulse generation and its applications to ultrafast spectroscopy are discussed. Femtosecond pulses of around 800 nm from a Ti:sapphire laser are used as a pump of an optical parametric amplifier (OPA) in a non-collinear configuration to generate ultrashort visible (500–780 nm) pulses and deep-ultraviolet (DUV, 259–282 nm) pulses. The visible-NIR pulses and DUV pulses were compressed to 3.9 fs and 10.4 fs, respectively, and used to elucidate various ultrafast dynamics in condensed matter with a sub-10 fs resolution by pump-probe measurements. We have also developed a 128-channel lock-in amplifier. The combined system of the world-shortest visible pulse from the OPA and the lock-in amplifier with the world-largest channel-number can clarify the sub-10 fs-dynamics in condensed matter. This system clarified structural changes in an excited state, reaction intermediate, and a transition state. This is possible even during molecular vibration and reactions via a real-time-resolved vibronic spectrum, which provides molecular structural change information. Also, ultrafast dynamics in exotic materials like carbon nanotubes, topological insulators, and novel solar battery systems have been clarified. Furthermore, the carrier-envelope phase in the ultrashort pulse has been controlled and measured.     

A CW seeded femtosecond optical parametric amplifier

1 Introduction Optical parametric amplification (OPA) based on femtosecond Ti:sapphire regen-erative amplifiers has been widely adopted in wavelength extension of ultrashort opticalpulses[1]. While BBO-based femtosecond optical parametric amplifiers have alreadycommercialized, the tuning range of such an 800 nm-pumped OPA is typically between1.15 μm and 2.6 μm due to the limited transparent range of BBO. From application’spoint of view, ultrashort pulses near 1 μm and between 3 and 4 …     

Stacking chirped pulse optical parametric amplification

Stacking chirped pulse optical parametric amplification based on a home-built Yb³⁺-doped mode-locked fiber laser and an all-fiber pulse stacker has been demonstrated. Energic 11 mJ shaped pulses with pulse duration of 2.3 ns and a net total gain of higher than 1.1 × 10⁷ at fluctuation less than 2% rms are achieved by optical parametric amplification pumped by a Q-switched Nd:YAG frequency-doubled laser, which provides a simple and efficient amplification scheme for temporally shaped pulses by stacking chirped pulse.     

20-50-fs pulses tunable across the near infrared from a blue-pumped noncollinear parametric amplifier

A two-stage blue-pumped noncollinearly phase matched optical parametric amplifier was used to generate near-infrared pulses that were continuously tunable from 865 to 1600 nm. The pulse lengths scaled from 20 fs at the shorter wavelengths to below 50 fs at 1600 nm, with a nearly Fourier-transform-limited bandwidth. From 200 muJ of 775-nm pump light at a 1-kHz repetition rate and a 130-fs duration, 7-2.5-muJ pulse energies were generated, corresponding to a typical quantum efficiency of 25% from blue to near-infrared light.     

High-power top-hat pulses from a Yb master oscillator power amplifier for efficient optical parametric amplifier pumping

We demonstrate shaping of high-energy broadband Yb amplifier pulses for the generation of a (sub)picosecond top-hat temporal pulse profile that significantly improves pumping efficiency of an optical parametric amplifier (OPA). Phase-only modulation is applied by an acousto-optic programmable dispersion filter. This simple scheme is scalable to a high average power due to a relatively broad bandwidth of the Yb:CaF(2) gain medium used in the amplifier that supports a sub-150-fs transform-limited pulse duration. Additionally we show that OPA seeding with supercontinuum remains possible because top-hat-shaped pulses passed through a glass block recompress to ≈200 fs with minimum satellite production.     

Generation of shaped ultraviolet pulses at the third harmonic of titanium-sapphire femtosecond laser radiation

We experimentally demonstrate a method to generate shaped femtosecond laser pulses in the ultraviolet at a central wavelength of 267 nm, the third harmonic of conventional titanium-sapphire femtosecond laser systems. Employing a 128-pixel liquid-crystal spatial light modulator, we impose variable spectral phase modulations upon the near-infrared laser pulses. By this, complex laser pulses can be shaped whose overall spectrum is still conserved. Our experiments show that it is possible to easily transfer these pulses into the ultraviolet at 267 nm via sum-frequency mixing in nonlinear crystals and to predictably generate multistructured ultraviolet femtosecond laser pulses. We analyze the temporal and spectral composition of these pulses after frequency conversion into the ultraviolet using difference-frequency cross-correlation and XFROG (cross-correlation frequency-resolved optical gating) techniques with an unmodulated fundamental laser pulse. The method can be employed to facilitate adaptive quantum control experiments in the ultraviolet wavelength regime, where the major absorption bands of many organic molecular systems are located. PACS 42.65.Re; 42.72.Bj; 32.80.Qk