Assessment of image resolution improvement by phase-sensitive optical parametric amplification

Classical information theory can be used to quantify the resolution performance of optical imaging systems. When an optical parametric amplifier (OPA) operated as a phase-sensitive amplifier (PSA) in the transverse spatial domain is used for point source imaging, the angular resolution improvement can approach the de Broglie resolution (i.e. Heisenberg limit). In this paper, classical information theory is employed to quantify the signal-to-noise ratio (SNR) improvement for both an ideal and a realistic multimode PSA applied to the problem of sub-Rayleigh imaging. When only considering the noise originating from the detector, the SNR improvement is found to scale quadratically as a function of the PSA gain, in the limit of noise power comparable to signal power. Differences in performance of an ideal PSA and a realistic PSA are discussed.     

Numerical simulation of spatial fluctuations in parametric image amplification

We study the properties of the spatial fluctuations in the far-field parametric fluorescence output of a type 1 degenerate traveling-wave parametric amplifier. Results of a semi-classical simulation are compared with experiments in a LBO crystal. This simulation is then used to predict amplified images of a continuous background, in a phase-sensitive as well as in a phase-insensitive configuration. Received 12 March 2001     

Coherence phenomena in the phase-sensitive optical parametric amplification inside a cavity

We theoretically and experimentally demonstrate coherence phenomena in optical parametric amplification inside a cavity. The mode splitting in the transmission spectra of a phase-sensitive optical parametric amplifier is observed. Especially, we show that a very narrow dip and peak, which are the shape of a delta function, appear in the transmission profile. The origin of the coherence phenomenon in this system is the interference between the harmonic pump field and the subharmonic seed field in cooperation with dissipation of the cavity.     

Coherent synthesis of ultra-broadband optical parametric amplifiers

We report on coherent synthesis of two ultra-broadband optical parametric amplifiers, each compressed by chirped mirror pairs, resulting in almost-octave-spanning (520-1000 nm) spectra supporting nearly single-cycle sub-4 fs pulse duration. Synthesized pulse timing is locked to less than 30 as by a balanced optical cross-correlator. The synthesized pulse is characterized by two-dimensional spectral interferometry and has a 3.8 fs duration.     

Numerical studies of optical parametric chirped pulse amplification

Based on the coupled wave equations, optical chirped-pulse parametric amplification (OPCPA) is simulated and its characteristics are investigated under the conditions of small-signal and pump depletion. The influence of the group-velocity mismatch and the phase mismatch among the three waves on the process of the amplification are discussed, respectively. Compared with the conventional chirped-pulse amplification system, synchronization between pump and signal-pulses is a crucial issue in OPCPA. The requirement on Δτ_p–s as well as the stability of the system is investigated.     

啁啾脉冲参量放大特性的数值模拟研究

根据啁啾脉冲激光参量放大技术,数值模拟了光参量放大在啁啾脉冲放大中的应用。研究啁啾脉冲参量放大增益及时间特性,特别是在大信号注入与小信号注入两种有代表意义的情况下,详细地分析了群速度失配、相位失配对放大过程的影响。研究了泵浦光脉冲与信号光脉冲的时间同步要求,讨论了放大系统的稳定性。     

Cavity-enhanced optical parametric chirped-pulse amplification

A novel method for the generation of high-energy ultrashort optical pulses is described and studied theoretically and numerically. Through the combination of parametric amplification and enhancement cavities, this method opens a route to generate few-cycle pulses at unprecedented average power levels through the use of a low-energy, high average-power pump source and energy storage in the enhancement cavity. Dispersion in the enhancement cavity ceases to be a concern with the use of long pump pulses. Limitations set by the Kerr nonlinearity of the amplifier crystal are analyzed, and ways to overcome them using self-defocusing nonlinearities are discussed.     

近红外波段宽带时间低相干光参量放大技术

在激光驱动惯性约束核聚变研究中,具有宽带、低相干特性的时间低相干光源将有望降低激光与等离子体相互作用的不稳定性,成为新一代激光驱动装置的有力竞争者。实现高功率低相干光放大输出是低相干光驱动器能否应用于惯性约束聚变领域的核心。光参量放大具有大带宽、高增益、无热效应等优势,可避免能级型放大介质的光谱窄化问题,是实现宽带低相干光放大的有效方案。系统阐述了宽带时间低相干光参量放大技术的原理和技术特性,并基于实验验证了采用非共线相位匹配的近红外波段宽带时间低相干光级联参量放大过程,最终实现7×10⁷的放大增益和13.19%的转换效率。     

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.     

Analysis of ultra-broadband high-energy optical parametric chirped pulse amplifier based on YCOB crystal

A new type of optical parametric chirped pulse amplifier is designed and analyzed for the amplification of pulse centered at 808 nm.A novel crystal,yttrium calcium oxyborate YCa4O(BO3)3(YCOB),is utilized in the power amplification stage of optical parametric amplification(OPA).Noncollinear phase matching parameters in the xoz principle plane of YCOB,compared with those in BBO and DKDP,are analyzed by numerical simulation.The results show that YCOB rather than DKDP can be used in the power amplification stage of OPA to realize the amplification of chirped pulse to several joules with a gain bandwidth exceeding 100 nm.This can be used to gain a high intensity pulse of ～10 fs after the compressor.     

Gain in phase sensitive parametric image amplification

We report an experiment of type 2 parametric image amplification in a phase sensitive configuration. In the spatial frequency domain, the parametric gain corresponds to amplification or deamplification, depending on the relative phase of the input image with respect to the pump wave and on the spatial frequencies of the input image.     

具有腔内光放大的单共振光参量振荡器

推导了描述稳态运行，具有腔内光放大的环形腔单共振光参量振荡器(ICOASRO)的功率特性的高斯光束理论.在这种结构的单共振光参量振荡器(SRO)中，适当地选择光放大器的参数，可以很大程度地降低单共振光参量振荡器的抽运阈值.在平均场近似下无二阶非线性交叉耦合作用的具有腔内光放大的环形腔单共振光参量振荡器的工作范围分成四个工作区域，且存在最小的单共振光参量振荡器的抽运阈值.文中的分析考虑了作为光放大器的激光增益介质的端面抽运特性，考虑了一般化单共振光参量振荡器的特性. 关键词： 单共振光参量振荡器 光放大 阈值     

Pulsed optical parametric oscillators with intracavity optical parametric amplification: a critical study

It is known that the idler conversion efficiency of optical parametric oscillators (OPOs) can be increased by adding a second nonlinear crystal in the cavity. This crystal is pumped by the signal and acts as an optical parametric amplifier (OPA) for the idler. However, this technique unavoidably increases the oscillation threshold because of additional losses and increased build-up time due to cavity lengthening. In this paper, we investigate both theoretically and experimentally the benefits and drawbacks of this so called OPO–OPA configuration versus the singly resonant OPO (SRO) configuration. Calculations are found to be in agreement with an experimental study of a SRO and an OPO–OPA operating near 3.4 μm both pumped by a 90-mJ 27-ns Nd:YAG laser. Our study reveals that the OPO–OPA needs to be driven at least two times above threshold to produce more idler energy than the SRO. In addition, near 3 μm the OPO–OPA is particularly efficient given that the difference frequency wave generated in the second crystal is also output coupled. PACS 42.65.Yj; 42.65.Sf     

Absolute radiance imaging using parametric image amplification

We show that parametric image amplification can be used to achieve a 2D radiance map directly expressed in photons per spatiotemporal mode. Radiance images of incoherent signals with less than one photon per mode (typically 10(-2)) are resolved.     

宽带光参量放大过程中的转换效率提升

建立了宽带光参量放大数值模拟平台,并基于此对宽带光参量放大系统的能量转换效率提升进行优化设计,根据模拟计算结果可以对实验中能够达到的最优化能量转换效率进行预判。建立了验证实验平台并进行了实验,研究并攻克了实验中遇到的参量荧光抑制、信号光,泵浦光空间精确匹配、脉宽精确匹配、时间波形整形等关键技术难点。在抑制参量荧光的同时实现了宽带光参量放大过程能量转换效率的提升,在单级宽带光参量放大过程中获得了30%的能量转换效率。     

宽带光参量放大过程中的转换效率提升

建立了宽带光参量放大数值模拟平台,并基于此对宽带光参量放大系统的能量转换效率提升进行优化设计,根据模拟计算结果可以对实验中能够达到的最优化能量转换效率进行预判。建立了验证实验平台并进行了实验,研究并攻克了实验中遇到的参量荧光抑制、信号光,泵浦光空间精确匹配、脉宽精确匹配、时间波形整形等关键技术难点。在抑制参量荧光的同时实现了宽带光参量放大过程能量转换效率的提升,在单级宽带光参量放大过程中获得了30%的能量转换效率。     

Pump-noise transfer in optical parametric chirped-pulse amplification

We report on direct observation of temporal contrast degradation of short pulses amplified by optical parametric chirped-pulse amplification. We show that, despite injection seeding, quantum-noise-induced fast modulations (< 50 ps) of the temporal profile of the pump pulse are imprinted on the spectrum of the amplified chirped pulse and give rise to a large picosecond pedestal in the time domain.     

Flat and ultra-broadband two-pump fiber optical parametric amplifiers based on photonic crystal fibers

A two-pump fiber optical parametric amplifier (FOPA) based on the photonic crystal fiber (PCF) in the telecommunication region is investigated numerically. The fiber loss and pump depletion are considered. The influences of the fiber length, input signal power, input pump power, and the center pump wavelength on the gain bandwidth, flatness, and peak gain are discussed. The 6-wave model-based analysis of two-pump FOPA is also achieved and compared with that based on the 4-wave model; furthermore, the gain properties of the FOPA based on the 6-wave model are optimized and investigated. The comparison results show that the PCF-based two-pump FOPA achieves flatter and wider gain spectra with less fiber length and input pump power compared to the two-pump FOPA based on the normal highly nonlinear fiber, where the obtained results show the great potential of the FOPA for the optical communication system.     

Investigation of spectral bandwidth of optical parametric amplification

The spectral bandwidth of three-wave-mixing optical parametric amplification has been investigated. A general mathematical model for evaluating the spectral bandwidth of optical parametric amplification is developed with parametric bandwidth and gain bandwidth via three-wave noncollinear interactions. The spectral bandwidth is determined by expanding the wave-vector mismatch in a Taylor series and retaining terms through second order. The model takes into account the effects of crystal length, noncollinear angle, group velocity, group-velocity dispersion and gain coefficient. The relation between parametric bandwidth and gain bandwidth is clearly defined. The model is applied to a BBO OPA, a LBO OPA and a CLBO OPA. PACS 42.65.Yj; 42.65.Lm; 42.65.Ky; 42.60.By     

Phase sensitive parametric amplification of optical vortex beams

Optical vortex beams with different topological charges are amplified in a travelling wave phase sensitive parametric interaction. Amplified beams observed either in the near field or in the far field domains exhibit patterns that depend on the relative phase between the pump and the vortex beams. Experimental results are compatible with the conservation of orbital angular momentum of the input beam whatever phase matching conditions.