The main characteristics (power loss and selectivity, resonance radiation divergence) of a two-mirror unstable resonator with a variable geometric configuration are investigated in the diffraction approximation based on the Fox-Lee equations. A cavity of an unstable confocal geometric configuration was adopted as a basic. At that, the control of the configuration of the resonator and resonance radiation is realized by deforming one of the mirrors (either a concave reflector or a convex counter-reflector). In this work, a comparative analysis of the active resonators characteristics with a deformable reflector and a deformable counter-reflector with the same functions of deformation is carried out. It is shown that, depending on the resonator specific technical parameters and the required power losses, the required concave reflector deformations amplitude in some cases is up to ~ 10% less than in the case of counter-reflector deformations. The mode selectivity of the considered active resonators is practically the same. The considered algorithms for controlling the shape of deformable mirrors make it possible to vary the resonator power losses and control the output laser radiation power over a wide range while maintaining the optical quality of radiation close to diffraction. The results of this work can be used to optimize the scheme and parameters of a laser with a controlled output radiation power.
The main characteristics of a three-mirror laser resonator (mode selectivity, resonance radiation divergence) are theoretically investigated. The resonator cavity contains two spherical mirrors that make up an unstable confocal resonator, and one flat semitransparent mirror, which is located perpendicular to the unstable confocal resonator optical axis. A flat mirror returns part of the radiation into confocal resonator cavity. It is shown that the considered three-mirror optical system as a laser resonator combines the properties of both unstable and stable resonators. The intensity of the focused beam with a Fresnel number of ~10, which is formed by an optical transmitter with a three-mirror resonator, is ~10% higher than in the case of a system with a two-mirror resonator. The results of this work can be used in development of large-size lasers with a low-gain active medium.
In the Fresnel approximation, a laser beam with field phase random distortions is represented by the sum of diffraction-limited and scattered component. Analytical and semi-analytical relationships are obtained that approximate the flux radiation distribution function with a relative error of a few percent depending on the size of the receiver and its distance without limiting the amplitude and scale of field phase random distortions. It is accepted in the work that phase random distortions are distributed according to the normal law, are statistically homogeneous, and have a Gaussian correlation function. The axial intensity, radius of the beam and its caustic is studied depending on the phase distortions parameters. It is established that the phase distortions presence can lead to the appearance of a second maximum in the intensity distribution along the optical axis and a shift of the global maximum closer to the optical system output aperture. The research results can be used in the development of optical transmitters and adaptive optical systems, in tomographic studies of laser radiation, in the development of methods for measuring parameters and determining the optical quality of laser beams and optical systems.
The model of calculation of a cavity configuration of the axially diode pumped solid-state laser which considers
nonlinear dependence thermo-optics distortions (a thermal lens) in the active element on the pumping power has been
presented. Quantity (focal distance) of a thermal lens in the crystal has been determined by means of Hartmann method.
Within the bounds of model the main spatial characteristics of the output laser radiation - the energy divergence angle and
output beam diameter for two cases of cooling of the active element were determined. It is shown that experimental
investigation of beam quality of the laser radiation is in correlation conformity with theoretical calculations.
The method of measurement of thermo-optical distortions (a thermal lens) in the active element Nd:YVO4 arising under axial diode pumping which distinctive feature is simplicity of processing and speed of reception of results of measuring have been described. Investigations were realized by means of Hartmann method based on monitoring of parameters of pumping radiation wave-front passing through investigated optical element. It is shown, that the proposed method enables direct investigation of thermo-optical distortions in small pumped areas (hundreds and tens micrometers). Presented is a method for research of thermo-optical distortions in an active element ensuring direct measurement of high orders aberrations.
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