The absorption and emission properties of transition metal (TM)-doped zinc chalcogenides have been investigated to understand their potential application as room-temperature, mid-infrared tunable laser media. Crystals of ZnS, ZnSe, and ZnTe, individually doped with Cr/sup 2+/, Co/sup 2+/, Ni/sup 2+/, or Fe/sup 2+/ have been evaluated. The absorption and emission properties are presented and discussed in terms of the energy levels from which they arise. The absorption spectra of the crystals studied exhibit strong bands between 1.4 and 2.0 /spl mu/m which overlap with the output of strained-layer InGaAs diodes. The room-temperature emission spectra reveal wide-band emissions from 2-3 /spl mu/m for Cr and from 2.8-4.0 /spl mu/m for Co, Cr luminesces strongly at room temperature; Co exhibits significant losses from nonradiative decay at temperatures above 200 K, and Ni and Fe only luminesce at low temperatures, Cr/sup 2+/ is estimated to have the highest quantum yield at room temperature among the media investigated with values of /spl sim/75-100%. Laser demonstrations of Cr:ZnS and Cr:ZnSe have been performed in a laser-pumped laser cavity with a Co:MgF/sub 2/ pump laser. The output of both lasers were determined to peak at wavelengths near 2.35 /spl mu/m, and both lasers demonstrated a maximum slope efficiency of approximately 20%. Based on these initial results, the Cr/sup 2+/ ion is predicted to be a highly favorable laser ion for the mid-IR when doped into the zinc chalcogenides; Co/sup 2+/ may also serve usefully, but laser demonstrations yet remain to be performed.

Transition metal-doped zinc chalcogenides: Spectroscopy and laser demonstration of a new class of gain media

Stability conditions for a ring resonator with an even number of mirrors and a nonplanar axial contour are studied analytically. New explicit expressions are derived to describe the transverse field distribution of the Gaussian mode with general astigmatism produced in this resonator. Field characteristics for a resonator with the specified parameters are calculated.

Analytical description of a Gaussian beam in a ring resonator with a nonplanar axial contour and an even number of mirrors

Based on the ray matrix theory, we theoretically analyzed the property of the optical axis perturbation
versus L/r (L means the total length of the resonator and r is the radius of curvature of the mirrors in the resonator) in the
nonplanar ring resonators by using statistical method for the first time as we know in this paper. The results show that the
root mean square of the optical axis tilt change evidently versus L/r while the optical axis decentration have a subtle
change versus L/r for the case that the mirror misalignments are confined in a certain scope and chosen arbitrarily. From
the perspective of optical axis perturbation, we can find the configuration parameters with which the optical axis
perturbation in the resonator responds violently to the mirror radial displacement or misalignment angle. These
interesting findings are important for cavity design, improvement, and alignment of nonplanar ring resonators.

Statistical analysis on the optical axis perturbation in nonplanar ring resonators

Combining with the self-consistent condition and extended 5 × 5 matrix, we theoretically analyzed the polarization properties of the eigenmodes throughout the nonplanar ring resonators with different structures. According to the satisfactory cross section size of the eigenmodes, a comparative study of the stability properties of these nonplanar ring resonators is also provided, and the three dimensions stability space of these resonators are presented for the first time as far as our knowledge goes. The results show that the major and minor axes of the cross section change with the propagation distance and have a symmetrical point for resonators with two different structures, and the area of the stable region for these resonators can be extended by changing the incident angles of the laser beam or the radii of mirror surfaces in the resonator. These interesting results are important for designing and arranging the diaphragm in ring resonators with a nonplanar structure, as well as optimizing the structure of the resonators themselves.

Analysis on propagation properties of the eigenmodes in nonplanar ring resonators

Theoretical analysis and experimental research on the polarization properties of output light in gyro are carried out to investigate the phenomenon that the amplitude of an output voltage signal is modulated by dither bias in laser gyros consisting of totally reflecting prisms. Taking the effect of prism stress birefringence into account, an analytical formula of the output light intensity in the gyro and the relationship between the polarization parameter and the amplitude modulation of the output signal are obtained and discussed. For the first time, the polarized power value of the output light is adopted as a basis to estimate the output signal amplitude fading extent of laser gyros. Experimental results demonstrate that when the value of polarized power of output light is below 25.5% of that in ideal static case, the standard error is over 0.0337 dBm, and the displacement extent of the prism is higher than 53% of the radius of the beam waist in the gyro cavity, the amplitude modulation extent of gyro output signal can reach up to 16%, which badly influences the measurement accuracy of the laser gyro. Using this polarized power detecting measurement method can repair the gyro immediately during its fabrication process, improve the testing and production efficiency and shorten the product development cycle.

https://iopscience.iop.org/article/10.1088/1674-1056/21/12/124206/pdf

Polarization properties in a prism laser gyro with mechanical dither bias

The structure of the fundamental mode field in a nonplanar ring four-mirror resonator with an aperture is determined taking into account rotations of the amplitude and phase distributions of an astigmatic Gaussian beam The rotation angles of the axes of these distributions are calculated upon variations in the characteristic aperture size and the angle of curvature (nonplanarity) of the resonator The effect of the resonator aperture and nonplanarity on the intensity distribution of the interference pattern behind a mixer is studied It is shown that interference fringes have a slope depending on the orientations of the amplitude and phase distributions of the mode

Amplitude—phase mode structure of an astigmatic Gaussian beam in ring lasers with a nonplanar four-mirror cavity and an aperture

We report our recent progress towards a multifrequency solid-state ring laser gyro, based on the YAG:Cr4+ broadband gain medium and operating in the mode-locking regime. Improved stability and reduced noise are achieved as the result of mode-locking. A model of the bidirectional generation dynamics during mode-locking, based on the Lamb theory, is provided. The readout system of beat signals of counterpropagating waves is demonstrated. The influence of the phase and the depth of modulation on the stable mode-locking is measured. Furthermore, lasing parameters, ensuring maximum accuracy of angular measurements, are determined.

Multifrequency Solid-State Ring Laser Gyroscope Based on YAG:Cr 4+

In this paper we present methods of measurement and reduction of the magnitude of coupling of counterpropagating waves in a laser gyroscope when it operates with a frequency biasing. The proposed complex methods for measuring this quantity are based on the amplitude modulation of one of the waves and the phase restoration of the beat signal. The obtained values of the waves coupling magnitude were used to control piezoelectric actuators that regulate the gyroscope cavity geometry in order to minimize the counterpropagating waves coupling. The magnitude of the coupling decreased in 2-5 times.

Measurement and active reduction of the coupling of counterpropagating waves due to scattering in a laser gyroscope when it operates with a frequency biasing

This work was carried out for Zeeman four-frequency laser gyro’s accuracy increasing. In order to obtain beat signals from two pairs of generated waves the laser gyro is complemented with an optical radiation mixer, which distributes the orthogonal circular polarizations waves rays to different photodetectors. The orthogonal circular polarizations waves magnetic sensitivities difference is taken into account to increase the accuracy of a four-frequency laser gyro. Measurement error’s magnetic component compensating method is proposed.

Four-frequency Zeeman laser gyro’s counterpropagating waves signals processing methods

The research conducted in this work, was aimed at finding conditions that suppress the influence of the magnetic field on zero drift in Zeeman four-frequency and quasi-four-frequency laser gyroscopes. We determined the optimal areas within the gain contour in the active medium. During operation in those areas the maximum suppression of the influence of the magnetic field on the drift of the gyroscope is provided. A gyroscope control system that switches gyroscope to the regime of minimum magnetic sensitivity has been created. We obtained weakening of the effect of the magnetic field on zero drift by more than three orders of magnitude.

Creation of Conditions for the Maximum Suppression of Magnetic Field Influence on Zero Drift in Four-Frequency and Quasi-Four-Frequency Zeeman Laser Gyroscopes

A.A. Fomichev

Papers

Amplitude—phase mode structure of an astigmatic Gaussian beam in ring lasers with a nonplanar four-mirror cavity and an aperture

Multifrequency Solid-State Ring Laser Gyroscope Based on YAG:Cr 4+

Measurement and active reduction of the coupling of counterpropagating waves due to scattering in a laser gyroscope when it operates with a frequency biasing

Four-frequency Zeeman laser gyro’s counterpropagating waves signals processing methods

Creation of Conditions for the Maximum Suppression of Magnetic Field Influence on Zero Drift in Four-Frequency and Quasi-Four-Frequency Zeeman Laser Gyroscopes