A dynamic phase-conjugate mirror based on CdF<Subscript>2</Subscript> crystals with bistable centers

A four-wave phase-conjugate mirror on reflection gratings recorded in a CdF₂ crystal with bistable centers has been studied experimentally. The mirror reflectivity and speed have been measured, and the coefficient of third-order nonlinearity of this medium has been estimated. The quality of the wave reflected from the phase-conjugate mirror has been investigated in model experiments.     

腔镜形变对圆筒组合型CO_2激光器模式的影响

针对具有锁相结构的圆筒组合型CO2激光器,分析了其注入锁定的原理,利用等价条形腔理论,建立了分析其输出基模的数学模型。利用该模型,研究了不同形变量对圆筒形腔输出基模的影响。结果表明,为了获得与注入光束模式类似的光场分布,复曲面镜与圆筒形谐振腔中平面镜镜面中心的形变量应控制在0.07倍波长以内。同时,分析在不同腔镜参数情况下腔镜形变对输出模式造成的影响,其结果有利于进一步优化谐振腔的参数设计。     

Dynamically reconfigurable characteristics of a double phase conjugate mirror using Sn2P2S6 crystals and their application to optical inter-satellite communication

A double phase conjugate mirror (DPCM), created by two mutually incoherent beams entering photorefractive nonlinear materials, can generate a phase conjugate beam whose reflectivity may be greater than 100%. Even though the conditions of the incident beams are changed, the DPCM can be dynamically reconfigured by using a Sn₂P₂S₆ crystal with a high response speed. These features of the DPCM are advantageous, particularly in an optical inter-satellite communication system. In particular, use of the phase conjugate beam from the DPCM offers wavefront compensation and amplification in satellite communication. In addition, the dynamically reconfigurable DPCM using a Sn₂P₂S₆ crystal relaxes the acquisition accuracy of the signal beam in the system. In this study, the temporal and spatial operating characteristics of the DPCM using a Sn2P2S6 crystal were first clarified. Next, an inter-satellite system based on the DPCM was proposed, and it was demonstrated that our system significantly improves the tolerance of the acquisition accuracy and tracking time.     

Study for dual-function EUV multilayer mirror

Studying the distribution of He⁺ in Earth's plasmasphere by detecting its resonantly scattered emission at 304 Å will record the structure and dynamics of the cold plasma in Earth's plasmasphere on a global scale. EUV imaging systems usually utilizes near-normal incidence optics including multilayer mirror and filter. In this paper, the space condition of the Earth's plasmasphere to confirm the expected performance of mirror were analyzed. In order to achieve higher response at 304 Å and reduce 584 Å radiation for the optical system, a new multilayer coating of Mo/Si with UO₂ was developed. Based on optical constants of Mo, Si and UO₂, we used a simplest method to compute the reflectance of this new multilayer mirror range from 100 to 584 Å. The results show the desirable thickness of UO₂ is 17 Å, and the multilayer mirror has a high reflectance of 26.10% at 304 Å and a low reflectance of 0.52% at 584 Å.     

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     

Compensation of dynamic phase distortions in the phase conjugation system based on the film of azocontaining liquid-crystalline polymer

The compensation dynamics of phase distortions in optical phase conjugation (OPC) using the film of azocontaining liquid-crystalline polymer was experimentally investigated. The quality of compensation of distortions of the wave front was determined, and the effect of experimental conditions on the OPC dynamics was studied. The coefficient of reflection in OPC reached 35% for a total incident light intensity of ～17 mW/cm² at a wavelength of 532 nm. The response time of the OPC system was ～1 s at a polymer temperature of 69°C. The high-quality compensation of the wave front distortions of the laser radiation was obtained. The residual error of compensation decreased by a factor of ～100 during the transient OPC process. It is demonstrated that the spatially modulated light beam can be retrieved during repeated passages through a phase plate with strong small-scale aberrations.     

Collimation of the initial wavefront of a partially coherent light beam by the backscattered signal

The possibility of compensating distortions of the initial wavefront of a partially coherent beam by the backscattered radiation power is analyzed. A new algorithm for controlling the flexible mirror by the signal of the volume atmospheric scattering is proposed and its efficiency is studied. It is shown that the developed algorithm makes it possible to considerably reduce the compensation time of distortions compared to the gradient method.     

Effect of the dynamic characteristics of adaptive mirrors on the efficiency of compensation for atmospheric distortions

In calculations of the efficiency of adapative systems for atmospheric paths, no consideration is usually given the dynamic properties of the wave-front correctors or of the automatic control system as a whole. The present article examines a self-consistent problem of dynamic compensation for atmospheric distortions by means of an adaptive mirror controlled by piezoelectric drives.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, No. 8, pp. 11–17, August, 1987.     

Dynamic wave-front distortion compensation with a 134-control-channel submillisecond adaptive system

A 134-control-channel adaptive-optics system consisting of a microelectromechanical mirror array (mu -mirror), a wave-front tilt-control mirror, and a very large scale integration controller utilizing a stochastic gradient-descent optimization of a performance metric is presented. A maximum adaptation rate of ~11, 000 iterations/s was achieved. The system was used to demonstrate real-time compensation for dynamic phase distortions from a laboratory-generated turbulence simulator in a laser-focusing experiment.     

Hybrid output mirror for optically pumped far infrared lasers

A hybrid metallic mesh multilayer dielectric coating mirror has been developed for use as an output mirror for optically pumped far infrared lasers. The metallic mesh provides a high reflectance in the far infrared while the multilayer dielectric coating is chosen to provide a maximum reflectivity at the pump wavelength (10 μm). This hybrid mirror has increased the output power of a CH₃F waveguide laser at 496 μm by a factor of 350 over that obtained with a hole coupling mirror. In addition, this mirror results in a far infrared output beam which has a minimum angular divergence limited only by the particular oscillating transverse waveguide mode (the EH₁₁ mode for this experiment).     

Design and fabrication of Gires�CTournois interferometers for?Yb-doped photonic crystal fiber laser system

A Gires?CTournois interferometer (GTI) with large dispersion compensation was designed and fabricated according to the requirement of the Yb-doped photonic crystal fiber laser system. The designed GTI can provide an average group delay dispersion (GDD) of ?1500 fs² and a high reflectance (>99.7%) from 1030 to 1050 nm. The Ion-assisted Deposition (IAD) technique was utilized to manufacture the mirror. Good agreement between the measured and designed results both for reflectance and GDD was achieved. The reflectance during 1030?C1050 nm was above 99.5% and the GDD ripple was less than ±300 fs². The GTI was used both in the intracavity dispersion compensation and extracavity pulse compression for the Yb-doped photonic crystal fiber laser system. A mode-locked soliton pulse with a 506-fs duration was recorded. An extracavity pulse compression test showed that the GTI had identical pulse compression capability as the conventional grating pairs while the energy loss was obviously reduced. Our results demonstrated that the HDM, which was able to provide quite a large amount of negative dispersion (???8×10⁴ fs²), could be an ideal alternative to replace the dispersive compensating grating pairs for the dispersion compensation of the Yb-doped photonic crystal fiber laser system.     

成像光谱仪扫描镜运动准确度测量

扫描镜的运动准确度直接影响成像光谱仪对地运动补偿效果,为此研制了一套扫描镜运动准确度测试设备对其进行测量.首先分析了扫描镜的运动补偿原理,从理论上给出了运动补偿曲线;随后以15 m地面像元分辨率和系统调制传递函数下降2%作为依据分别确定了扫描镜的位置和速度准确度要求,列出了扫描镜运动补偿倍数与相对转速误差的关系.基于检定设备1/3法则提出了扫描镜运动准确度测试设备技术指标要求,接着以0.8″绝对式光电编码器为核心建立了一套扫描镜运动准确度测试装置,并从测试方法误差和编码器测角误差两方面对测试装置测角和测速准确度进行了详细分析;最后采用研制的测试装置对扫描镜的运动准确度进行了测量试验.试验结果表明扫描镜位置准确度优于3″±1.2″,4倍补偿时速度准确度为5.6%±1.29%,6倍补偿时速度准确度为3.85%±1.29%,满足成像光谱仪对扫描镜运动准确度要求.外场成像图像证明本文提出的扫描镜运动准确度测量方法及设备可用于成像光谱仪扫描镜的性能检测与验收.     

钛宝石飞秒激光器用色散补偿Gires-Tournois镜的研究

根据钛宝石飞秒激光器的色散补偿要求设计了单次反射平均补偿量为-60 fs²的GT(Gires-Tournois)镜,采用离子束辅助沉积技术结合光学监控技术制作了器件.用分光光度计对650—950 nm波段薄膜反射率进行测试,结果表明反射率测试曲线与设计曲线十分符合,同时利用白光干涉系统对群延迟色散进行了测试,测试结果与设计符合得很好,实际的色散曲线振荡基本控制在±20 fs²以内.应用该GT镜进行钛宝石飞秒激光系统的色散补偿,取得了很好的锁模效果,得到了29 fs的超短脉冲. 关键词： 色散补偿 钛宝石飞秒激光器 GT镜 离子束辅助沉积     

The possibility of compensating small-scale wavefront distortions with a Zernike cell and a spatial light modulator in an optical feedback scheme

The possibility of compensating small-scale wavefront distortions in an optical feedback scheme by using a spatial light modulator optically addressed by the output beam of a Zernike cell is theoretically considered. The optimal parameters of the system for compensating sinusoidal distortions and distortions characteristic of phasing of subapertures, the requirements for the elements of the system, the range of compensated distortions, and the quality of compensation are determined. It is shown that the use of this method makes it possible to compensate small-scale phase distortions with a peak-to-peak amplitude of up to 3λ; in this case, the gain in the Strehl number can be as high as 80.     

On the possibility of compensating for small-scale wave-front distortions using a Zernicke cell and an optically controlled spatial light modulator

The possibility of compensating for small-scale wave-front distortions using a spatial light modulator which is optically controlled by the output beam of a Zernicke interferometer was studied theoretically. The optimal parameters of the system, requirements of its elements, the range of the compensated distortions, and the compensation quality are determined for the case of compensation for sinusoidal distortions. It is shown that this technique allows for the compensation of small-scale sinusoidal phase distortions with a depth of up to 3λ and a 20-fold gain in the Strehl number can be achieved.     

Line Narrowing of a Tunable High Pressure CO2 Laser by Means of an Improved Non-Littrow Cavity

A model is reported to foresee ,for different mirror choices, the spectral properties of a high pressure, frequency tunable, CO₂ laser, operating with a non-Littrow grating mounting. The calculations show a larger frequency selectivity for not collimated plane cavities. The model is experimentally verified in a suitable high pressure laser. In particular narrowed linewidths less than 300MHz ( FWHM) are obtained.     

Study on the possibilities of controlling the laser output beam properties by an intracavity deformable mirror

The possibilities of controlling the laser beam properties by a deformable mirror introduced into the laser optical cavity were studied theoretically and experimentally. The experiments were performed under conditions of an industrial high power transverse flow cw CO₂ laser operating with a stable resonator of a folded configuration. A deformable bimorph mirror of a surface profile controlled by the voltage applied to the mirror electrodes is implemented to the laser system as a back cavity mirror or as a one of the inner folding mirrors. The near-and far-field characteristics of the laser beam versus the resonator configuration controlled by the changes of the focal length of the deformable mirror are discussed in the paper. The analysis reveals that the resonator with an inner deformable mirror is much more sensitive to the mirror curvature variations than the resonator in which the deformable mirror is used as a back cavity mirror. The presented results show that dynamic and controllable changes in the resonator properties result in the controlled modification and optimisation of the laser output power and spatial parameters of the laser radiation.     

Diode-pumped passively mode-locked yb<Superscript>3+</Superscript>-doped yttrium lanthanum oxide ceramic sub-picosecond laser

A diode-pumped sub-picosecond laser is realized with Yb³⁺-doped yttrium lanthanum oxide transparent ceramic Yb:(Y_0.9La_0.1)₂O₃ as the gain medium for the first time. By using Gires-Tournois interferometer mirrors and chirped mirror for dispersion compensation and semiconductor saturable absorber mirror for passive mode-locking, laser pulse as short as 730 fs was obtained at the central wavelength of 1033 nm and repetition rate of 65.5 MHz. Under the maximum pump power of 6 W at 976 nm, the output power is 92 mW.     

Propagation of super-Gaussian field distributions

The near- and far-field propagation of initially super-Gaussian field distributions is discussed. upon propagation, the beam profile is shown to undergo distortions of a magnitude which increases with the super-Gaussian order. These distortions can lead to a significant increase of the on-axis intensity in the near-field. The beam quality, evaluated both in terms of the beam parameter product and theM ² factor, is shown to decrease as the super-Gaussian order gets larger. These calculations also illustrate the difficulties associated with theM ² factor when characterizing the propagation of a beam with increasingly sharp edges. The effect of the transmission of the super-Gaussian field through a super-Gaussian graded-reflectivity mirror (GRM) is also discussed. The results of this study have direct implication in the domain of GRM resonator design.     

变形镜受热变形引起的波前畸变仿真及补偿

针对变形镜自身受强激光辐照后热变形问题,利用ANSYS的多物理模型建立了变形镜的热机械模型并进行了计算。针对受强激光辐照后变形镜吸收了部分热量并产生了0.9μm的变形量,根据该变形镜热畸变分布特征,提出了一种利用补偿镜对热畸变进行补偿的方法,即在一个薄型镜面背后用一些约束头固定构成补偿镜,放置在变形镜的后续光路中。约束头在补偿镜上的位置与极头在变形镜上的位置对应错开分布。对三种不同形状约束头的补偿镜进行了计算,补偿后综合变形量降低到0.35,0.32和0.40μm。利用光束传输因子(BPF)对理想光束通过补偿镜后的效果进行评价,结果表明通过三种补偿镜后BPF值从0.906提高到了0.966,0.971和0.957。进一步的计算表明,补偿效果受约束头尺寸的影响较小。