基于光程差扫描的低相干离轴数字全息术

针对在低相干离轴数字全息术中,光源相干长度限制物光波可探测面积的问题,提出了一种基于光程差扫描的低相干离轴数字全息记录方法.首先,通过改变参考光和物光波之间的光程差,使得干涉条纹扫描记录平面的不同区域,而后对各个区域的数字全息图采用数值再现的方法获取不同区域处的物光波相位分布,最后采用相位拼接技术拼接各个区域的相位分布实现物光波的全视场探测.     

大景深全息图的拍摄

本文利用激光的时间相干性对光程差的准周期性特点,采用光程差为腔长的偶数倍的物光照明以获得大景深全息图的拍摄,用普通的一米腔长的He-Ne激光器成功地拍摄了面积5m~2,景深8.2m的全息图,为全息技术在使用普通市售激光器情况下应用于工程技术拍摄大型结构开辟了很好的远景。     

大场景全息照相实验中若干问题的探讨

大场景、大景深全息照相术已有一些文章介绍与报道[1-3].近年来,我们初步获得了景深为250cm,场景面积为100×250cm2和视场角优于120°的广角大场景全息图[3].为进一步提高大场景全息图的质量,普及大场景全息术,从而开拓大场景的全息应用,本文对大场景全息照相实验中的若干特殊问题进行探讨,并给出相应的理论分析与实验结果. 一、场景面积与景深的扩展 一般全息照相的条件之一是物光波与参考光波的光程差小于光源的有效相干长度.对于大场景、大景深全息照相,由于光源相干长度的有限性,此程差条件尤为重要.采用光程补偿法[2,3]或选取光程差为…     

相干长度可连续调谐的半导体激光器

实验利用光反馈的方法获得了相干长度连续可调的半导体激光光源.通过调节反馈强度及抽运电流,有效控制了光反馈半导体激光器的相干长度.其相干长度可由无反馈时的几米连续调至100 μm.同时,利用光反馈半导体激光器速率方程,数值模拟了反馈强度及抽运电流对半导体激光器相干长度的影响.实验及数值模拟均表明：通过调节反馈强度的大小可以有效控制半导体激光器的相干长度,光反馈半导体激光器的相干长度随反馈强度的增大而减小,而偏置电流对相干长度无明显影响.模拟结果与实验结果符合. 关键词： 光反馈半导体激光器 相干长度 反馈 混沌     

对大场景全息照相方法的改进

大场景全息照相是全息照相的重要内容之一,它对拍摄较大的静态物体和贮存文物信息起重要作用。实现大场景全息照相的方法一般采用光程补偿法和根据激光器性质而采用光程差为激光器腔长偶数倍的方法。这两种方法都需较好的防震装置和强激光光源,且光路复杂,调整麻繁,给大场景全息图的拍摄及普及带来一些困难。大场景全息照相与普通的小场景全息照相的差异在于它需要有一个较大的,能够把景物的全部信息(振幅和位相)加以记录的相干区域,要获得好的干涉效果,要求其光程差必须小于所用光源的相干长度。     

观测有效相干长度及TC周期性的全息法

本文根据J.Upatinieks的椭圆等光程原理,提出了一种现场观测多纵模激光有效相干长度及其TC周期性的全息法.介绍了基本原理与方法,给出了相应的实验结果.     

全光纤激光相干合成光谱响应特性研究

基于N-腔镜谐振腔理论对全光纤激光相干合成进行了理论分析，数值模拟了迈克尔逊型相干合成激光器的光谱特性，对两个光纤Bragg光栅的中心波长差和两路光的光程差对合成光谱特性的影响给出了理论解释.用啁啾光纤光栅取代其中一个光纤Bragg光栅，使激光相干合成的带宽由0.3 nm拓展到1.0 nm.     

基于弹光调制的红外光谱吸收法在室内VOC检测中的研究

为了保证静态干涉系统在气体定性定最分析方面稳定性高、抗干扰能力强的特点,设计了基于弹光调制实现光程静态扫描的干涉检测系统.系统由红外激光器、起偏器、弹光调制器、检偏器及CCD组成.通过弹光调制器使弹光晶体的主折射率随调制信号周期性的变化,从而产生周期性变化的光程差.通过对调制相位变化的计算,可知得到调制度随晶体长度、调...     

纵模分裂式正交偏振双频He-Ne激光器

在激光器谐振腔中放入单轴石英晶体,由于石英晶体对o光和e光的折射率的不同,所以,在同一谐振腔中o光和e光有不同的光程和谐振频率.将其称之为模式分裂效应.利用这一效应可以制成频率达几十兆赫兹的双频激光器.针对原有理论与实验结果之间的某些差异,建立了一套分析该种类型双频激光器的理论.根据所建立的理论着重分析了谐振腔光轴与晶轴夹角α对激光器频差的影响.并绘出了He-Ne激光管L<150nm和150nm相似文献   

激光全息照相景深扩展实验探讨

对于具有较大景深的物体,全息照相常常不能一次得到全部清晰的物像,即在物像上局部模糊甚至出现暗区,其主要原因是物体的景深超出了激光器的相干长度所能允许的最大景深限度.利用光程补偿的方法,借以达到扩展全息照相景深的目的,使之在激光器的相干长度范围内.     

Numerical analysis with active phase matching of multi-line deuterium-fluoride laser beam array

Coherent beam combination can promote the emitting power of chemical laser in the extremely high power application. To achieve chemical laser coherent combining the optical paths of each channel should be adjusted to the same for the multi-line spectral characteristic and the combination effect is highly dependent on the optical path variance. The dependence of the combination effect on the optical path variance is calculated taking deuterium-fluoride (DF) laser for example. The feasibility and the validity of the multi-line chemical laser coherent combining are discussed with different optical path variances. The coherent combination of multi-line chemical laser is not totally unattainable as long as the precise optical path control measure is involved. To achieve excellent combination effect for chemical laser with ordinary optical path control measure, line-selecting technology is commonly needed.     

Group delay locking of coherently combined broadband lasers

We demonstrate a method for single-detector coherent sensing and automated coalignment of group delays in a coherently combined laser array, enabling robust coherent combining of broadband sources despite initial path mismatches exceeding the laser coherence length. The method is based on Fourier-domain filtering of the coherently combined laser beam to extract error signals, and it is equally applicable to controlling both spatial and temporal misalignments.     

Determination of phase fluctuations of a Highly-Stabilized laser by the analysis of photon echo decay functions

The simple 2-pulse echo as a prototype of coherent spectroscopy offers the unique possibility for a recall of past time parameters. This feature is utilized in the optical frequency domain for the realization of a phase comparator, equivalent to an optical interferometer of approximately 10 km variable path length difference. The measured autocorrelation time of the optical field is a convenient absolute measure of the frequency stability of the laser field and has been tested in the 10–100 kHz line width range.     

Optical fibers with interferometric path length stability by controlled heating for transmission of optical signals and as components in frequency standards

We present a simple method to stabilize the optical path length of an optical fiber to an accuracy of about 1/100 of the laser wavelength. We study the dynamic response of the path length to modulation of an electrically conductive heater layer of the fiber. The path length is measured against the laser wavelength by use of the Pound–Drever–Hall method; negative feedback is applied via the heater. We apply the method in the context of a cryogenic resonator frequency standard. PACS 42.81.Wg; 07.07.Mp; 07.07.Tw     

Long-external-cavity distributed Bragg reflector laser with subkilohertz intrinsic linewidth

We report on a simple, compact, and robust 780 nm distributed Bragg reflector laser with subkilohertz intrinsic linewidth. An external cavity with optical path length of 3.6 m, implemented with an optical fiber, reduces the laser frequency noise by several orders of magnitude. At frequencies above 100 kHz the frequency noise spectral density is reduced by over 33 dB, resulting in an intrinsic Lorentzian linewidth of 300 Hz. The remaining low-frequency noise is easily removed by stabilization to an external reference cavity. We further characterize the influence of feedback power and current variation on the intrinsic linewidth. The system is suitable for experiments requiring a tunable laser with narrow linewidth and low high-frequency noise, such as coherent optical communication, optical clocks, and cavity QED experiments.     

半导体激光器及其在干涉计量中的应用

本文介绍了半导体激光器的典型特性,探讨了用其相干长度进行干涉计量的新方法,并进行了眼球光学长度的测量的实验。     

Reduction of parasitic interferences in digital holographic microscopy by numerically decreased coherence length

Due to the large coherence length of laser light, optical path length (OPL) resolution in laser based digital holographic microscopy suffers from parasitic interferences caused by multiple reflections within the experimental setup. Use of partially coherent light reduces this drawback but requires precise and stable matching of object and reference arm’s OPLs and limits the spatial frequency of the interference pattern in off-axis holography. Here, we investigate if the noise properties of spectrally broadened light sources can be generated numerically. Therefore, holograms are coherently captured at different laser wavelengths and the corresponding reconstructed wave fields are numerically superimposed utilizing variable weightings. Gaussian and rectangular spectral shapes of the so synthesized field are analyzed with respect to the resulting noise level, which is quantified in OPL distributions of a reflective test target. Utilizing a Gaussian weighting, the noise level is found to be similar to the one obtained with the partially coherent light of a superluminescent diode. With a rectangular shaped synthesized spectrum, noise is reduced more efficient than with a Gaussian one. The applicability of the method in label-free cell analysis is demonstrated by quantitative phase contrast images obtained from living cancer cells.     

Third-order nonlinearity of Er3+-doped lead phosphate glass

In a laser coherent combination, the phase detection and control is the most critical. Using the beat frequency method, consistence of the phase in output beams can be ensured through real-time detection and correction for the phase change. Phase noises are controlled by a liquid crystal phase modulator. At the same time, the liquid crystal polarization controller is used to make the polarization state stable, which is good for the improvement of the combining efficiency. The wave length of the main oscillation laser is 532 nm. The output power of laser can be adjusted continuously from 0 to 6 W. The shifted frequency of the system is 40 MHz. The accuracy for phase control is superior to λ/70 RMS. In the process of closed-loop control, using the liquid crystal phase and polarization controller, a better signal phase correction of optical path has been achieved for the coherent combination of high power laser arrays.     

共光路移相单频激光干涉测长系统

单频激光干涉系统采用偏振光移相方法,用来解决常规单频激光干涉仪中的光强"零漂"问题。共光路设计提高了干涉系统的测量稳定性和重复性。采用光程差放大技术提高了干涉系统的分辨力。在构造了一套实验布局的基础上,分析了影响系统测长精度的主要因素,并对干涉系统的测量误差分量做了定量的分析,完成了系统的精度测试。     

基于光程编码与相干合成的三维超分辨术

光学相干层析成像的轴向分辨率和横向分辨率是互为独立的,其轴向分辨率由系统光源带宽和探测光束的聚焦条件共同决定,而横向分辨率由系统样品臂的聚焦条件决定. 提高光学相干层析成像的轴向分辨率的方法主要基于宽带光源技术以及变迹术与相干门相结合的方法,而这些方法对于横向分辨率并没有提高. 提出了一种通过光程编码与相干合成的方法,可以同时提高其轴向分辨率和横向分辨率. 通过在光学相干层析成像系统的样品臂中加入光程编码分束器形成多种对应不同光程延迟的有效响应函数,基于光学相干层析成像术固有的光程分辨能力可以得到同一样品对应于不同有效响应函数的多幅图像. 通过数字控制不同有效响应函数的相对贡献对其进行相干合成,可以同时实现轴向和横向的超分辨效果. 与以前的方法相比,光程编码与相干合成方法简单易行、成本低廉,不仅可以避免系统复杂和价格昂贵等不足,而且可以同时较大幅度地提高系统的轴向分辨率和横向分辨率. 关键词： 光学相干层析成像 轴向超分辨 横向超分辨 光程编码