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In this experiment, the stable output of a dual-frequency laser source is obtained by an acousto-optic modulator due to the Bragg diffraction effect. Furthermore, the non-polarized dual-laser heterodyne interferometer is designed to measure the micro-movement of stacked piezoelectric (PZT) ceramic. This micro-movement can be dynamically determined by comparing the phase difference between the conference beam and measuring beam. The results indicate that the micro-movement of PZT ceramic changes linearly with the driven-voltage in the range of 0–30 V and the sensitivity of movement to voltage is 58.3 nm/V, which is very close to the theoretical value and this laser heterodyne interferometer can be applied for calibrating parameters of PZT ceramic.

• The influence of the acousto-optic frequency shifter (AOFS)'s thermal-induced birefringence (TIB) on laser frequency-shifted feedback (LFSF) system is usually ignored by users but seriously affects the stability of the system especially startup stability. • Analyze the phenomenon of amplitude and phase of frequency-shifted signal cause by AOFS's TIB, such as the amplitude variation, phase fluctuation, phase jump and phase temperature drift. • The methods to eliminate or suppress these negative influences are proposed by principal axis alignment or quasi-common-path compensation. • This study improves the startup stability and shorten startup preheating time of the LFSF system, which also has guiding significance to other heterodyne interference systems. The acousto-optic frequency shifter (AOFS) is the key component of the laser frequency-shifted feedback (LFSF) system, and its thermal-induced birefringence (TIB) seriously affects the stability of the system. In this paper, the influence of the AOFS's TIB on LFSF system is analyzed, and the method of suppressing this influence is proposed. The theoretical model of LFSF considering the AOFS's TIB is established, and the influence on both amplitude and phase of frequency-shifted signal is analyzed. When the AOFS starts working, its TIB effect is obvious due to the accumulation of working heat, which makes the polarization state of its diffraction light change dynamically in most cases. The laser feedback imaging system and laser feedback displacement measurement system are built separately to evaluate the amplitude and phase stability. By principal axis alignment or quasi-common-path compensation, the amplitude variation, phase fluctuation, phase jump and phase temperature drift caused by the AOFS's TIB can be eliminated or suppressed. This study improves the startup stability and anti-ambient temperature interference ability of the LFSF system, which also has guiding significance to other heterodyne interference systems. [ABSTRACT FROM AUTHOR]

The modulation of degree of spatial coherence (DOSC) plays an optical gating which highly correlates with the coherence volume (CV) in the proposed DOSC laser scanning confocal fluorescence microscope (DOSC-LSCFM). The axial resolution at sub-diffraction-limit performance was demonstrated and discussed. • Ability of the modulation DOSC gating able to reduce the specimen-induced aberrations and scattering in DOSC-LSCFM. • The modulation DOSC gating and sub-diffraction-limit performance in DOSC-LSCFM. • Experimental result in consistence with the developed DOSC-LSCFM image formation theory. [ABSTRACT FROM AUTHOR]

Traditional displacement measurement systems by grating, which purely make use of fringe intensity to implement fringe count and subdivision, have rigid demands for signal quality and measurement condition, so they are not easy to realize measurement with nanometer precision. Displacement measurement with the dual-wavelength and single-grating design takes advantage of the single grating diffraction theory and the heterodyne interference theory, solving quite well the contradiction between large range and high precision in grating displacement measurement. To obtain nanometer resolution and nanometer precision, high-power subdivision of interference fringes must be realized accurately. A dynamic tracking down-conversion signal processing method based on the reference signal is proposed. Accordingly, a digital phase measurement module to realize high-power subdivision on field programmable gate array (FPGA) was designed, as well as a dynamic tracking down-conversion module using phase-locked loop (PLL). Experiments validated that a carrier signal after down-conversion can constantly maintain close to 100 kHz, and the phase-measurement resolution and phase precision are more than 0.05 and 0.2 deg, respectively. The displacement resolution and the displacement precision, corresponding to the phase results, are 0.139 and 0.556 nm, respectively. [ABSTRACT FROM AUTHOR]

The heterodyne interferometer using acousto-optic modulation is presented to measure the frequency response of photodetectors (PDs) utilized in ultrasonic applications by optical methods. The heterodyne signal is served as the excitation source. The measurement frequency more than 150 MHz can be achieved by two serial or parallel connected acousto-optic frequency shifters (AOFSs) in the interferometer. The frequency shift of AOFSs can be adjusted continuously, so that the frequency resolution of the measurement better than 500 kHz is easy to realize. The experimental results for two PDs with bandwidth 150 and 50 MHz are discussed. The presented scheme can also be used to characterize the PDs in the frequency range of megahertz for other optical measurement applications. [ABSTRACT FROM PUBLISHER]