Frequency-shifted optical feedback in a pumping laser diode dynamically amplified by a microchip laser

Compared with conventional optical heterodyne detection, laser optical feedback imaging (LOFI) allows for a several orders of magnitude higher intensity modulation contrast. The maximum contrast amplification is typically 10(3) for a diode laser in the gigahertz range and 10(6) for a microchip laser in the megahertz range. To take advantage of the wavelength tunability of a laser diode and of the lower resonant detection frequency of a microchip laser, we used LOFI modulation induced by the frequency-shifted optical feedback in a laser diode as a modulated pumping power for a microchip laser for resonant dynamic amplification. In this way, we were able to transfer the optical feedback sensitivity of the laser diode to the megahertz range. Application to telemetry is also reported.     

Tunable blue laser compensates for thermal expansion of the medium in holographic data storage

A tunable laser optical source equipped with wavelength and mode-hop monitors was developed to compensate for thermal expansion of the medium in holographic data storage. The laser's tunable range is 402-409 nm, and supplying 90 mA of laser diode current provides an output power greater than 40 mW. The aberration of output light is less than 0.05 lambdarms. The temperature range within which the laser can compensate for thermal expansion of the medium is estimated based on the tunable range, which is +/-13.5 degrees C for glass substrates and +/-17.5 degrees C for amorphous polyolefin substrates.     

Mars Observer Laser Altimeter: laser transmitter

The Mars Observer Laser Altimeter utilizes a space-qualified diode-laser-pumped Q-switched Nd:YAG laser transmitter. A simple numerical model of the laser energetics is presented, which predicts the pulse energy and pulse width. Comparisons with the measured data available are made. The temperature dependence of the laser transmitter is also predicted. This dependence prediction is particularly important in determining the operational temperature range of the transmitter. Knowing the operational temperature range is especially important for a passive, thermally controlled laser operating in space.     

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。     

异步应答激光测距技术

异步应答激光测距可实现卫星距离及星地时差测量.本文给出的主波时差公式与经典公式,以及一种拟工程实现、且与异步应答激光测距原理相同的无线电测距方法给出的工程应用公式不同.为了探求正确的主波时差公式,掌握这种测距体制的测距精度,进而验证异步应答激光测距体制的工程可行性,本文设计并开展了异步应答激光测距技术验证实验,利用两个地面测距终端对卫星反射测距模拟了星地异步应答激光测距过程.该实验是我国对异步应答激光测距体制的首次实践.实验研究结果表明,异步应答激光测距可用于两终端之间距离和主波时差的精确测量,且本文给出的主波时差公式正确,经典公式与应用公式存在不妥之处.     

Precisely tunable, narrow-band pulsed dye laser

Anarrow-band, precisely tunable dye laser pumped by an injection-seeded YAG laser is described. The laser achieves an output of 100 mJ/pulse and 40% efficiency when one uses Rhodamine 6G dyes. The output pulse is Gaussian both in time and spatial profile. The laser oscillator employs an intracavity étalon that is repetitively pressure scanned over one free spectral range while the grating successively steps to consecutive étalon modes. We pressure scanned the étalon under computer control using a bellows. Methods are described for calibrating the tuning elements for absolute precision. We demonstrated that the laser has an absolute precision of ±0.4 pm over a 1.0-nm scan. This accuracy is achievable over the wavelength range of a dye.     

Laser ablation threshold dependence on pulse duration for fused silica and corneal tissues: experiments and modeling

The surface ablation threshold fluence of fused silica and two porcine cornea layers, the epithelium and the stroma, is characterized as a function of the laser pulse duration in the range of 100 fs-5 ps for a wavelength of 800 nm (Ti:sapphire laser system). The plateaulike region observed between 100 fs and 1 ps for the corneal layers indicates that for use in laser surgery, laser pulse durations chosen within this range should be practically equivalent. Our model predicts that the ablation threshold will decrease rapidly for pulse durations in the low end of the femtosecond regime.     

水下激光成像系统探测距离的计算与仿真

为了估计水下激光成像系统的工作距离,根据水下激光成像系统的成像过程,通过分析目标的辐射特性,水体的衰减特性等各因素,建立了水下激光成像系统的信噪比模型.根据识别目标所需要的信噪比阈值、脉冲激光器等器件的性能指标,推导出水下激光成像系统的工作距离公式,并且完成了系统成像距离的计算与仿真.采用532 nm的Nd∶YAG固体激光器、自组ICCD相机以及基于FPGA技术设计的同步控制电路板,进行了距离选通水下激光成像实验.实验结果表明:理论模型计算的信噪比与实际图像的信噪比平均误差为1.37 dB,证实了该模型的合理性.     

Extending the continuous tuning range of an external-cavity diode laser

The continuous tuning range of an external-cavity diode laser can be extended by making small corrections to the external-cavity length through an electronic feedback loop so that the cavity resonance condition is maintained as the laser wavelength is tuned. By maintaining the cavity resonance condition as the laser is tuned, the mode hops that typically limit the continuous tuning range of the external-cavity diode laser are eliminated. We present the design of a simple external-cavity diode laser based on the Littman-Metcalf external-cavity configuration that has a measured continuous tuning range of 1 GHz without an electronic feedback loop. To include the electronic feedback loop, a small sinusoidal signal is added to the drive current of the laser diode creating a small oscillation of the laser power. By comparing the phase of the modulated optical power with the phase of the sinusoidal drive signal using a lock-in amplifier, an error signal is created and used in an electronic feedback loop to control the external-cavity length. With electronic feedback, we find that the continuous tuning range can be extended to over 65 GHz. This occurs because the electronic feedback maintains the cavity resonance condition as the laser is tuned. An experimental demonstration of this extended tuning range is presented in which the external-cavity diode laser is tuned through an absorption feature of diatomic oxygen near 760 nm.     

A review of laser fabrication of metallic engineering components and of materials

Abstract

The state of the art and directions for the future development of two laser based technologies, direct laser fabrication in which powder is fed into the focal point of a laser, and a laser powder bed technology are outlined in this review. The areas in which these technologies have made significant contributions are: the manufacture, directly from powder, of alloys and of functionally graded materials which enables a range of compositions to be assessed rapidly and the manufacture of net shape and the repair of engineering components. It is suggested that rapid assessment of structure/property relationships in a range of compositions will continue to be a useful application of laser fabrication. It is further concluded that the two approaches, direct laser fabrication and laser powder bed will continue to be developed since each has its own advantages and disadvantages; direct laser fabrication is the preferred technique for alloy development work and for component repair but laser bed technology is currently the preferred technology for the manufacture of small components which require a good surface finish. Improvements in surface finish, in dimensional accuracy, in microstructural control and in process control with real time feedback to control properties are nevertheless required if these technologies are to increase their impact in the area of the manufacture of net shape components.     

Frequency locking of tunable diode lasers to a rubidium-stabilized ring-cavity resonator

We demonstrate a technique for locking the frequency of a tunable diode laser to a ring-cavity resonator. The resonator is stabilized to a diode laser that is in turn locked to an atomic transition in rubidium, thus giving it absolute frequency calibration. The principal advantage of the ring-cavity design is that there is no feedback destabilization of the laser. The cavity has a free-spectral range of 1.3 GHz and Q of approximately 35, which provides robust locking of the laser. The locked laser is able to track large scans of the cavity.     

Three-dimensional imaging laser radar with a photon-counting avalanche photodiode array and microchip laser

We have developed a threedimensional imaging laser radar featuring 3-cm range resolution and single-photon sensitivity. This prototype direct-detection laser radar employs compact, all-solid-state technology for the laser and detector array. The source is a Nd:YAG microchip laser that is diode pumped, passively Q-switched, and frequency doubled. The detector is a gated, passively quenched, two-dimensional array of silicon avalanche photodiodes operating in Geigermode. After describing the system in detail, we present a three-dimensional image, derive performance characteristics, and discuss our plans for future imaging three-dimensional laser radars.     

脉冲自触发高精度测距技术的设计与实现

介绍了把脉冲自触发技术与双光路误差模型应用于激光测距系统，从而完成精密距离测量的一种测量技术。探讨了将脉冲自触发技术、恒比值时点判别技术以及光路系统误差修正技术相结合而实现的高精度时间测量的测量原理与实现，并根据实验结果进行了定性分析。     

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.     

Linearization of the frequency sweep of a frequency-modulated continuous-wave semiconductor laser radar and the resulting ranging performance

The performance of a frequency-modulated continuous-wave (FMCW) semiconductor laser radar has been examined. Frequency modulation (linear chirp) has been studied experimentally in detail. To create a linear frequency sweep, we modified the modulating function according to the measured frequency response of the laser, using an arbitrary function generator. The measurements indicate the possibility of achieving a spectral width of the signal peak that is transform limited rather than limited by the frequency modulation response of the laser, which permits the use of a narrow detection bandwidth. The narrow width results in a relatively high signal-to-noise ratio for low output power and thus also in relatively long-range and high-range accuracy. We have performed measurements of a diffuse target to determine the performance of a test laser radar system. The maximum range, range accuracy, and speed accuracy for a semiconductor laser with an output power of 10 mW and a linewidth of 400 kHz are presented. The influence of the laser's output power and coherence length on the performance of a semiconductor-laser-based FMCW laser radar is discussed.     

Backscatter-modulated laser diode for low-frequency small-amplitude vibration measurement

Feedback phenomenon in laser diodes is applied to low-frequency vibration measurement in the micrometer range on poorly reflecting targets. The laser diode is frequency modulated. Its beam is focused on the vibrating target, and backscattered light is fed back into the laser. The optical laser diode power variation is processed to measure the frequency and amplitude of low-frequency vibrations of amplitude, ~100 nm to 10 mum. Experimental results for sinusoidal and triangular vibrations are compared with theory.     

Experimental comparison of autodyne and heterodyne laser interferometry using an Nd:YVO₄ microchip laser

Using an Nd:YVO? microchip laser with a relaxation frequency in the megahertz range, we have experimentally compared a heterodyne interferometer based on a Michelson configuration with an autodyne interferometer based on the laser optical feedback imaging (LOFI) method regarding their signal-to-noise ratios. In the heterodyne configuration, the beating between the reference beam and the signal beam is realized outside the laser cavity, while in the autodyne configuration, the wave beating takes place inside the laser cavity, and the relaxation oscillations of the laser intensity then play an important part. For a given laser output power, object under investigation, and detection noise level, we have determined the amplification gain of the LOFI interferometer compared to the heterodyne interferometer. LOFI interferometry is demonstrated to show higher performance than heterodyne interferometry for a wide range of laser powers and detection levels of noise. The experimental results are in good agreement with the theoretical predictions.     

激光三角法距离传感：散斑的影响

描述了一个激光三角法距离传感，并用于鞋楦三维测量。讨论了系统的静态和动态测量误差，指出其深度分辨率主要由散斑决定，实验表明 ，增加透镜孔径或在成象透镜前加一随机振动位相掩膜均可极大改善深度分辨率。     

Numerical study of passive Q switching of a tunable alexandrite laser with a Cr:Y2SiO5 solid-state saturable absorber

Passive Q switching of a tunable alexandrite solid-state laser with a Cr:Y(2)SiO(5) solid-state saturable absorber is numerically studied over a major portion of the alexandrite tuning range. The theory of passive Q switching with a slowly relaxing saturable absorber is studied and utilized for evaluating the performance of the Cr:YSO Q-switched alexandrite laser system. With a typical laser configuration, a Q-switched laser pulse of 262 mJ in 23 ns is obtained.     

一种全新的激光自动跟踪方法在激光移动通信中的应用

介绍了传统激光移动通信的特点及其不足，提出一种基于MOEMS(微光机电系统)技术的全新的激光自动跟踪方法。给出一个基于这种方法的激光移动通信系统实例，这种系统结构简单、体积小、重量轻、功耗低、控制简便，在一定的角度范围内能够自动跟踪目标实现移动通信。实验研究结果表明，这种系统能够很好地满足激光移动通信所要求的功能。