Phase-difference amplification using a Sagnac interferometer

In this paper, we describe a new method for achieving phase-difference amplification, which is quick and convenient, operates in real time, and requires no photographic steps. Magnification factors of 2, 4 or 6 are achieved easily in one step. Because the system operates in real time, phase stepping may be applied to extract the amplified phase distributions. Our method is a variation on longitudinally reversed shearing interferometry, using first- or higher-order diffraction from a grating (hologram) which is in fact the interferogram of the wavefront under test. The grating is derived from a standard two-beam interferometer which is phase-stepped, and displayed in real time on a spatial light modulator in the phase-difference amplification setup. It is illuminated by the two output beams from a Sagnac interferometer, similar to the set up used by (Barnes et al. Barnes TH, Eiju T, Matsuda K. Appl Opt 1986; 25:1864). for spectral resolution enhancement, and a phase-amplified fringe pattern is obtained by spatial filtering using a Fourier transform lens. We demonstrate operation of the phase amplifier and show amplified phase maps retrieved by phase-stepping. We believe this is the first time that real-time phase amplification without photographic steps and with phase stepping has been demonstrated.     

Analysis of nonlinearity in a high-resolution grating interferometer

Metrological feasibilities of a high-resolution grating interferometer (GI) based on a transverse Zeeman laser are investigated. When the grating pitch equals 20 μm, a resolution of 0.7 nm is obtained by means of a heterodyne signal processing method. The comparison of two approaches for determining the residual nonlinearity is presented. One is to evaluate the maximum residual error by determining the amplitude modulation degree of the measurement signal. The other is to do a high precision calibration with a differential dual-frequency interferometer that has a higher precision. The experimental results show that the nonlinearity is no more than 25 nm which fits well with the estimating result. Analysis of the depolarization effect of the grating indicates that it has little influence on the measurement accuracy.     

两级喇曼压缩系统配偏振干涉仪诊断等离子体电子密度

 在星光Ⅱ铷玻璃激光装置上,采用两级喇曼压缩系统产生的波长为308 nm的紫外光作为探针束,配合Nomarski偏振干涉仪对金平面靶冕区激光等离子体进行诊断。308 nm光具有波长短、亮度高、脉冲时间短、相干性好的优点,作为探针束诊断冕区产生的等离子体电子密度,可以与高功率激光装置打靶激光同步,实现有效地脉冲压缩,同时避免等离子体中谐波分量的干扰。实验获得了308 nm紫外探针光偏振干涉条纹图,在研究Abel反演算法的基础上,利用自行研制的基于Windows操作系统的实验数据处理软件,对实验数据进行了处理和分析,得到了冕区等离子体电子密度的空间分布。结果表明：两级喇曼压缩系统配偏振干涉能有效抑制主束谐波影响,以更高时间分辨测量等离子体的更高密度区域。     

Observation of flux qubit states with the help of a superconducting differential double contour interferometer

The critical current of a new structure, the superconducting differential double contour interferometer (DDCI), investigated recently, depends on the parity of the sum of quantum numbers of the two superconducting loops connected in two points by two Josephson junctions. The theory confirms that the DDCI structure can be used for the ideal readout of quantum states of the flux qubit. Large jumps in the critical current and voltage enables to observe continuously the change in time the state of the flux qubit. Such observations can have fundamental importance for the investigation of macroscopic quantum systems with strongly discrete spectrum such as the flux qubit. The DDCI structure can also be used for precise measurement of a very weak magnetic field.     

Two-Photon Two-Focus Fluorescence Correlation Spectroscopy with a Tunable Distance Between the Excitation Volumes

In the present work, a Michelson interferometer was combined with a two-photon excitation microscope to perform two-focus Fluorescence Correlation Spectroscopy. This simple and original approach allows us to tune the distance between the two excitation volumes and determine absolute diffusion constants. The technique was validated on different model systems that demonstrate the sensitivity of the approach.     

Accuracy analysis and stabilization design of the Fabry–Perot frequency discriminator in double-edge wind lidars

The measurement error of a double-edge wind lidar caused by a disturbed Fabry–Perot interferometer (FPI) is analyzed. Several error sources such as air pressure variations, temperature changes, and mechanical vibrations are considered in the measurement-error model. The simulation results show that a double-edge wind lidar is so sensitive to environmental variations that the measurement error reaches ±60 m/s if the FPI is not stabilized. In order to compensate the external disturbance acting on the FPI, a nonlinear proportional–integral–derivative (PID) control scheme is designed based on the transmission measurement of the calibration channel. An arc tangent function is used to improve the feedback gain of the usual PID control design. The results show that with the new controller the measurement accuracy of the wind lidar can be improved 4–5 times in comparison with the usual control design, and the range of the measurement error is only ±3 m/s.     

System for measuring optical admittance of a thin film stack

A new method based on the polarization interferometer structure has been applied to measure the optical admittance, the refractive index and thickness of a thin film. The structure is a vibration insensitive optical system. There is one Twyman-Green interferometer part to induce a phase difference and one Fizeau interferometer part to induce the interference in the system. The intensities coming from four different polarizers were measured at the same time to prevent mechanical vibration influence. Using the polarization interferometer, the optical admittance, the refractive index and thickness of a single layer of Ta₂O₅ thin film has been measured. The measurement results were compared with the results obtained by ellipsometer. The results meet reasonable values in both refractive index and thickness.     

光声互作用模型中的Pancharatnam相位

通过解析求解简单极化激元模型的Pancharatnam相位, 研究了温度、耦合强度、声子与光子频率差、平均光子数等对其演化的影响. 结果表明,Pancharatnam相位随时间振荡,且振荡频率和振荡波形随时间变化,这种变化随着温度升高和耦合强度、声子与光子频率差增加而加大. 系统Pancharatnam相位随时间的演化在平均光子数较小时表现比较有规律,但随着平均光子数的增加,它趋于混沌化. 关键词： 极化激元 Pancharatnam 相位 Mach-Zehnder干涉仪 相干态     

模拟大气风场及其数据处理技术的研究

热层大气风速的测量可以采用干涉法来进行,由于光源（气辉辐射谱线）的强度很弱,故干涉法对测量系统要求很高。利用半导体激光器（LD）的调制特性和法布里-帕罗干涉仪(FPI)的高光谱分辨能力设计了一种用简单设备进行大气风场模拟与测量的方法。改变LD的驱动电流使其输出激光频率改变,从而模拟气辉辐射的多普勒频移,通过分析FPI获得的干涉图可检测出该频移,进而得到等效风速。模拟风速的相对误差不超过6.5%,最小模拟风速为20.01m/s,且测量结果与LD的线性调制特性很相符。使用该方法可以有效地对多普勒风速测量原理、数据处理方法、系统性能以及测量误差进行分析和评估。     

Real-time surface profile measurement using a feedback type of sinusoidal phase modulating interferometer

In this paper, we propose a sinusoidal phase modulating (SPM) interferometer that is insensitive to external disturbances, and its measuring principle is analyzed theoretically. In the SPM interferometer, the interference signal is detected by a high-speed image sensor based on a low-speed CCD and a signal processing circuit is used to obtain the phase of each point on the surface. Therefore, the surface profile can be measured real-time. The experiments measuring the surface profile of a wedge-shaped optical flat show that the measurement time of the SPM interferometer is less than 10 ms, the repetitive measurement accuracy is 4.2 nm. The results show that the impacts of nonlinear distortion of the piezoelectric transducer (PZT) and part external disturbance are removed.