RESUMO
We demonstrate an environment-noise-free optical heterodyne interferometer (OHI) based on a double-pass acousto-optic frequency shifter (AOFS) for phase retardation measurements. The OHI generates intermediate-frequency (IF) heterodyne beat signals for each orthogonal linear polarization mode of a birefringence sample. The phase differences of the IF signals are compared by using a wide-bandwidth lock-in amplifier. This scheme provides 20 dB rejection of common-mode environmental disturbances. Measurements of the half-wave voltage of an electro-optics modulator and the electro-optic coefficient of an LiNbO3 plate are demonstrated as application examples.
RESUMO
Depending on cavity configuration, a c-cut Nd:YVO4 laser by using a large-apex-angle axicon can execute azimuthally and radially polarized operations. A large-apex-angle axicon dominates and stabilizes the generation of the pattern, and expands the difference between the ordinary and extraordinary rays to generate off-axis cylindrical vector beams. When the cavity length is properly adjusted, the polarization of off-axis laser beams can exhibit a transition from azimuthal to radial polarization. The degree of polarizations can be up to 95.4% ± 2.6% and 94% ± 3.7% for azimuthally and radially polarized beams, respectively; and the slope efficiencies are approximately 20.5% for both polarized operations. Using two-pass-mode ray tracing, the ray generating mechanisms and divergent angles of their patterns were analyzed.
RESUMO
The iodine molecule has frequently been used as a frequency reference from the green to the near-infrared wavelength region (500-900 nm). We describe the frequency locking of the second-harmonic signal of a 197.2-THz (1520.25-nm) distributed-feedback diode laser to the absorption lines of the iodine hyperfine structure; a frequency jitter below 0.1 MHz was achieved at a 300-ms time constant. This scheme provides a simple, compact, and high-performance frequency reference in the optical communication band.