10～500 kHz水听器的激光外差干涉法原级校准

阐述了水听器在10～500 kHz频率范围的激光外差干涉法原级校准的原理和测量装置.利用激光外差干涉系统非接触测量水中反光薄膜在声波调制下引起的多普勒频移,经过零点信号解调算法得到水质点振速,准确复现水下声压量值,之后将水听器置于水中测量点完成对其自由场电压灵敏度的原级校准.对各误差因素进行了分析,详细给出了系统测量不...     

A CO2 laser rangefinder using heterodyne detection and chirp pulse compression

The sensitivities of heterodyne and direct-detection systems at CO₂ laser wavelengths are compared to illuminate the design principles involved. It is shown that destruction of the temporal coherence of scattered radiation is a significant effect when heterodyne systems are used on targets with internal motion. The complete system and the results obtained are then described. The compact optics head contains a waveguide laser, an acousto-optic modulator and SAW chirp devices; it has 45 mm diameter transmit and receive apertures. Whem many returns are integrated, ranges of several kilometres are obtained off natural targets with an accuracy of 10 m. From the Doppler shift off a moving target, radial velocity can be determined simultaneously with the range when an up-chirp/down-chirp technique is used; an accuracy of better than 1 m s^–1 is demonstrated.     

Investigation of glass panels thickness profile by all-fiber digital heterodyne interferometry

All-fiber digital heterodyne interferometry is a laser metrology technique employing pseudo-random codes phase modulated onto an optical carrier signal. In this heterodyne interferometer system, the optical signal includes signal reflected and transmitted from the sample, respectively. Compared with the conventional heterodyne interferometry, this enhanced optical system has much higher measurement sensitivity, and can distinguish the signal which reflected from the front and the rear surface of the sample. Analysis and simulation for the digital heterodyne interferometry are presented. It takes approximately 4 s to scan the whole surface with the diameter of 300 mm. The thickness profile of the sample is obtained in the experiment. The discussion about the experiment is given finally.     

Quasi-optical assessment of the ALMA band 9 front-end

The ALMA band 9 (600–720 GHz) receiver is a dual channel heterodyne system which is capable of detecting orthogonally polarised signals utilising a wire grid beam splitter. Two Superconductor–Insulator–Superconductor (SIS) mixers mounted behind hybrid mode corrugated horns are coupled to the 12 m Cassegrain antenna via a wavelength independent configuration of two off-axis elliptical mirrors.We outline an approach involving accurate physical optics simulations in conjunction with precise experimental measurements of the complete optical front-end which guarantees the highest performances. This practical verification approach can be generalised to all quasi-optical receivers to validate system performance. In this paper, we verify the optical design and estimate antenna system efficiency. Comparison between measurement and simulation indicates precise information is achievable in estimating system performance allowing potential improvements in ALMA instrument calibration accuracy.     

微探针纳米尺度振动测试的实验研究

微探针是扫描探针显微镜(SPM)的重要组成部件,其共振频率等振动特性直接影响系统的性能。给出了系统微探针共振频率的测试方法,对微探针在压电陶瓷驱动力作用下的受迫振动进行了有限元分析。提出了相位变化0.1°所对应的0.1nm位移分辨率的双频激光外差干涉光学测量系统,对微探针纳米尺度振动特性进行了测试对比实验,并对SPM标定样块进行了比对分析。实验结果验证了双频激光外差干涉测量方法的可行性和其应用价值。     

Tapered waveguide semiconductor raman laser

Semiconductor Raman laser can act as a heterodyne demodulator of terahertz-band modulated light wave signals in wideband optical communication systems. We have been developing the semiconductor Raman laser with a waveguide structure composed of a GaP core and Al_xGa_1–xP cladding layers. The tapered waveguide structure can reduce the threshold pump power by increasing the internal pump power density. Fabricated tapered waveguide semiconductor Raman laser have shown the threshold pump power of 160 mW. Discussion is made on the origin of losses as well as the limit of the low pump power operation.     

超外差干涉绝对距离测量研究综述

近几年来，基于多波长干涉理论的绝对距离测量技术取得了很大的进展。其中，超外差绝对距离干涉测量可以克服光学元件引起的模耦合误差，这是普通的外差干涉测量所不能避免的。超外差测量还能够实现合成波长相位的实时检测。本文简要介绍了多波长干涉测量（也叫小数重合法）的基本原理，论述和分析了超外差干涉测量的原理，指出了超外差测量的优点。最后，对超外差测量的方案进行了综述，并指出了它们在实际测量中的特点。     

Development of Transmission Optics for High-Power TEA CO2 Lasers and Methods of Increasing Laser-Radiation Resistance of Materials for High-Power IR Optics

The results of analytical and experimental investigations aimed at increasing laser-radiation resistance of materials for IR optics and developing high-power optics for microsecond TEA CO₂ lasers with energy per pulse up to 12–25 kJ and gas-dynamic CO₂ lasers with energy per pulse up to 130 kJ are presented. It is demonstrated that the integrated approach that combines the improvement of already existing technological methods and the development of novel technological methods for refining the parameters of materials for transmission IR optics (including techniques of growth of single crystals, strain hardening, and laser, ionic, and chemical treatment), the design and optimization of optical units (including the development of segmented transmission optics, the improvement of optical schemes for spatial formation of laser beams, the use of fast-response physical effects to screen optical elements from high-power fluxes of laser radiation) is necessary to solve this problem.     

Measurement of small displacement based on surface plasmon resonance heterodyne interferometry

This paper proposes an optical method for measuring small displacements using the surface plasmon resonance (SPR) heterodyne interferometry. A heterodyne light beam reflected by a mirror passes through a hemisphere glass and then enters into a surface plasmon resonance apparatus at the resonant angle. A small displacement of the mirror will introduce a phase-difference variation between p- and s-polarizations of the light emerging from the SPR apparatus. The phase-difference variation can be precisely measured with the heterodyne interferometric technique, and the associated displacement can be estimated. The feasibility of this method was verified by experiment, and the displacement measurement resolution of about 1.4 nm over a traveling range of 6 μm was achieved. Our method of measurement has the merits of both common-path interferometry and heterodyne interferometry.     

共路外差法分析牛顿望远镜偏振特性

应用共路外差干涉法分析了牛顿望远镜的偏振特性。根据菲涅耳定律求出了入射光s-偏光和p-偏光入射到望远镜各点的反射率公式。给出了共路外差干涉法测量牛顿望远镜偏振特性的实验装置原理图。采用632.8nm的外差光源,分析了牛顿望远镜对s-偏光和p-偏光反射系数、相位差以及对入射光偏振度的影响,根据入射角度的不同绘制了相应的变化曲线。结果表明：镀有铝膜的牛顿望远镜对入射光偏振特性影响较小,s-偏光和p-偏光反射系数相差不到0.01,偏振度变化不超过0.07,适用于激光遥感偏振成像的接收系统。     

临近空间相干激光通信链路外差效率分析

临近空间相干激光通信链路是天地一体化高速通信网络节点间连接的重要链路。围绕外差效率这一表征大气湍流扰动后信号光和本振光相干合成的指标,推导了非均匀湍流路径上的外差效率理论表达式,并结合大气折射率结构常数廓线,开展了临近空间-地面、临近空间-临近空间和临近空间-低轨卫星三类临近空间相干激光通信链路的外差效率仿真。仿真结果表明:临近空间-低轨卫星链路可以忽略大气对外差效率的影响;如果临近空间-临近空间链路距离大于500km或是临近空间-地面链路天顶角大于60°,外差效率将小于50%,有必要采用自适应光学技术进行补偿。     

Gaussian optical design of a submillimeter-wave and far-infrared laser sideband heterodyne spectrometer

A submillimeter-wave/far-infrared (SMM/FIR) laser sideband heterodyne spectrometer has been built for molecular rotational spectroscopy application in the frequency range of 600–3000 GHz. Based on Gaussian optics, optical system of the spectrometer is designed to be quasi-achromatic and low losses. In this article the optical design and the performance of the spectrometer are presented.     

频差偏差对全视场外差测量精度的影响

根据全视场外差测量的相关理论,推导了频差偏差与仪器测量精度的相互关系.分析了频差大小、频差偏差、采集初始时间、初始相位、采样频率和采样周期数等相关参数对测量精度的影响.研究结果可以作为全视场外差测量设备设计、参数选取的理论依据;并给出了通过合理选择采样时间和采样帧数提高测量精度的一种方法.     

Heterodyne interferometer for displacement measurement with amplitude quadrature and noise suppression

The high precision displacement measurement in nanoscale is crucial to many applications. We present a heterodyne interferometry with differential phase to amplitude conversion scheme for displacement measurement in nanoscale. In this approach, the differential phase introduced by the displacement is converted into the amplitudes of heterodyne signals in quadrature. Meanwhile, the heterodyne signals in phase quadrature are also achieved so that the displacement can be determined from the amplitude ratio of the quadrature signals, and the direction of displacement can be determined from the phase quadrature. Since the differential phase to quadrature amplitude conversion is achieved through the optical addition and subtraction by polarization tuning, which are based on differential detection concept. Thus the proposed method benefits from the features of differential detection with common phase noise and correlated amplitude noise rejection and that of quadrature detection with real time and wide dynamic range of phase measurement. To demonstrate the capability of proposed method in differential phase measurement, we measure the displacement drove by a commercially available PZT pusher and found close agreement between the experiment and the theory. The experimental evidence of noise suppression is also found with spectral measurements, which demonstrates the resolution of displacement measurement at 60 pm and minimum detectable differential phase of 5.6 × 10⁻⁶ rad/ over 50 kHz.     

Subpicometer length measurement using heterodyne laser interferometry and all-digital rf phase meters

We present an all-digital phase meter for precision length measurements using heterodyne laser interferometry. Our phase meter has a phase sensitivity of 3 μrad/√Hz at signal frequencies of 1 Hz and above. We test the performance of our phase meter in an optical heterodyne interferometric configuration, using an active Sagnac interferometer test bed that is flexible and low noise. We demonstrate more than 70 dB of laser frequency noise suppression to achieve an optical phase sensitivity of 5 μrad/√Hz and a corresponding displacement sensitivity of 0.5 pm/√Hz at signal frequencies above 10 Hz. In addition, we demonstrate the ability of our phase meter to follow full fringe signals accurately at 100 Hz and to track large signal excursions in excess of 10(5) fringes without cycle slipping. Finally, we demonstrate a cyclic error of ≤1 pm/√Hz, above 10 Hz.     

Heterodyne performance of a quasioptical Schottky diode detector: Theoretical and experimental results

A detailed theoretical and experimental study of the heterodyne performance of a quasioptical Schottky diode detector is presented. The experimental results have been obtained by mixing the radiation from a FIR laser with the output of a 67–73 GHz Klystron. The heterodyne signal variation versus various parameters and its relation to the special case of two lasers mixing are described. The mixer characteristics are a NEP value of 2×10^–19W/Hz and a detector bandwidth of at least 9 GHz. Experimental evidence of harmonics generation of submillimetric frequencies at the diode junction is also presented.     

Practical common-path heterodyne surface profiling interferometer with automatic focusing

In modern semiconductor and optics industries, there is a strong demand for a highly sensitive and non-contact surface profilometer. This paper describes a practical heterodyne surface profiling interferometer for on-line non-contact measurement which has been developed recently. The essential feature of the profilometer is a newly designed common-path configuration to minimize the effects caused by vibration, air turbulence and other environmental variations. A single-mode frequency-stabilized laser diode (780 nm) serves as the light source to make the whole system compact (total volume 250L×200W×100H mm). A powerful signal processing scheme is also developed, which includes three parts: automatic voltage control, phase measurement with wide range and automatic focusing control. All these make the repeatability and stability of the profiling interferometer greatly improved. The system has vertical resolution of 0.39 nm and lateral resolution of 0.73 μm. During approximately an hour, the stability is within 1.95 nm(3σ).     

Dynamic two-frequency interferometry for small displacement measurements

Two-frequency interferometry for small displacement measurements is examined from a practical point of view. A laser beam that is modulated sinusoidally in intensity by an acousto-optic Bragg cell provides signal and reference optical waves to produce dynamic interference. The output signal of a photodetector receiving the interference is composed of optical homodyne and heterodyne components. The heterodyne component carries a vibrational displacement to be detected on its amplitude. A sinusoidal vibration amplitude is measured down to 0.5 nm.     

Analysis of laser source nonlinearity due to longitudinal mode-hopping

The nonlinearity of a frequency-ramped single-mode laser source to be used in optical heterodyne interferometry has been investigated. The analysis is based on mode-hopping due to variation in injection current, temperature and mismatch reflections.     

Linearization methods of laser interferometers for pico/nano positioning stages

Presented work introduces methods for improving linearity of a heterodyne laser interferometer system. The heterodyne configuration exhibits high potential in demanding applications, like pico/nano positioning. Those applications require superior accuracy, more difficult to obtain in a homodyne configuration of the laser interferometer. The homodyne setup is more susceptible to external light, variation of DC offset and higher noises, especially the 1/f noise. Those issues are filtered out in the heterodyne configuration. The main disadvantage of heterodyne setup are higher measurement nonlinearities. In this paper there are first introduced sources of nonlinearities and their impact on the overall accuracy. According to those findings there are proposed techniques to eliminate error caused by parasite beams, i.e. nonlinearities. Presented method is based on digital signal processing and is reliable and easy to use. In the shown approach the nonlinearities correction is completely automatic. Such system is applicable for X/Y positioning stages. Presented configuration of the laser interferometer is able to track the displacement with 100 pm resolution up to 7 m/s of translation velocity. The resolution can be improved to 10 pm by limitation of maximal velocity. In the paper there is confirmed that errors caused by nonlinearities are in range of ±0.6 nm. Achieved accuracy is comparable to capacitance gauges with presented laser interferometer having much better dynamic range.