Many factors of intracavity perturbation will degrade the output power and beam quality for high power passive
Q-switched slab laser. In the paper, the experiment test on the output beam quality of a passive Q-switched zig-zag slab
Nd:YAG laser has been performed by adopting Hartmann-Shack (H-S) wavefront sensor and Zernike mode
reconstruction theory. In this way, the PV and RMS values of the wavefront aberration, every order zernike aberrations
can be acquired accurately, and the point spread function (PSF) of the beam and the distribution of circle energy can
also be obtained by further calculation, so the beam-quality can be known fully. The experimental results show that the
wavefront aberration of laser is mainly concentrated in the frontal 10 ranks of Zernike aberration, mainly including the
defocus A3, the low-order astigmatism A5, the coma aberration A6 and the spherical aberration A10 because of the crystal
thermal effect and the intracavity aberrated perturbation.
The results of an experimental and theoretical study of the proprerties of a LD pumped laser using a plano-concave
stable resonator are presented. The influence of thermal lens effect on laser output mode and beam quality has been
discussed briefly by using the transfer matrix theory. In this paper, further experiment on the output beam quality of a
LD pumped acousto-optic Q-switched laser has been also performed by adopting Hartmann-Shack wavefront sensor and
Zernike mode reconstruction theory. Using this method, the PV and RMS values of the aberration wavefront, the frontal
35-order Zernike aberrations can be acquired, and the Strehl ratio curve of the output beam and the distribution of circle
energy can also be obtained by calculation, so the mode properities can be fully understood. The experimental results
show that the beam wavefront aberration is mainly concentrated in the frontal 15 orders of Zernike aberration, mainly
including the defocus A3, the low-order astigmatism A4 and A5, and the coma aberration A6 and A7 because of the crystal
thermal effect.
Thermal effects of diode pumped solid-state lasers have been discussed briefly. The influence of thermal lens effect on
laser output mode and beam quality, and the compensation method for thermal lens effect are briefly analyzed by means
of transmission matrix optics. The functional relations between the thermal lens focal length and the beam spot size for a
plano-concave stable resonator have been calculated numerically. In this paper, further experiment on the output beam
quality of a laser diode pumped acousto-optic Q-switched laser has been also performed with Hartmann-Shack (H-S)
wavefront sensor and Zernike mode reconstruction theory. In this way, the PV and RMS values of wavefront aberration,
the frontal 35-order zernike aberrations can be acquired, and the point spread function (PSF) of beam and the distribution
of circle energy can also be obtained by calculation, so the output beam quality can be known fully. Experimental results
show that the wavefront aberration of laser is mainly concentrated in the frontal 15 ranks of Zernike aberration, mainly
including the defocus Z3, the low-order astigmatism Z4 and Z5, and the spherical aberration Z10 because of the thermal
effect of gain medium.
The experimental adjustment method for a positive-branch confocal unstable resonator has been studied and a method
for estimating the alignment for unstable resonators has been suggested. The output beam intensity and phase properties
should be used together to judge whether the unstable resonator is been aligned exactly. Firstly, the optical axis of the
resonator must be aligned and the intensity properties of output beam should be symmetrical distribution for the adjusted
unstable resonator, however, some high-order aberrations such as defocus may be still included in the outcoupled beam.
In this paper, the beam is detected by using Hartmann-Shack (H-S) wavefront sensor and the phase properties can be
further acquired by adopting Zernike mode-reconstruction theory. By such means, the phase PV and RMS values, the
35-order Zernike aberrations, and the distribution of circle energy can all be obtained, and the beam-quality can be
known fully. So the resonator can be adjusted according to the measured Zernike aberrations and also the ideal condition
of alignment can be acquired.
The effect of intracavity aberration perturbation on output mode structure properties of passive confocal unstable resonator is been experimentally researched by adopting Hartmann-Shack method on the basis of numerical simulation. The results show that intracavity tilt aberration affects the outcoupled intensity distribution, but only a small intracavity tilt perturbation will not obviously augment the high-order aberrations of beam phase properties. The tilt aberration, coma aberration and astigmatism will all be brought, and also tilt aberration is the main component when intracavity mirrors have a vertical movement along the direction of optic axis. When adaptive optical elements such as deformable mirrors are adopted for intracavity aberration correction, the correction for tilt aberration should be considered at first.
The influence on an outcoupled mode by introducing intracavity tilt perturbation in an unstable resonator is developed. The intra-cavity mode properties and Zernike aberration with the intracavity mirror's misadjustment are calculated theoretically. The experimental results about the relations of intracavity perturbation and the properties of mode aberration are presented by adopting a Shack-Hartmann (H-S) wavefront sensor. The results show that the intracavity perturbation of the concave mirror has a more remarkable effect on outcoupled beam quality than that of the convex mirror. For a large Fresnel-number resonator, the tilt angle of the intracavity mirror has a near-linear relationship with the extracavity Zernike tilt coefficient. The ratio of the tilt aberration coefficient approaches the magnification of the unstable resonator if equivalent perturbation is applied to the concave and convex mirrors, respectively. Furthermore, astigmatism and defocus also increase with tilt aberration of the mode. So an intracavity phase-corrected element used in an unstable resonator will be most effective when placed as near as possible to the concave mirror plane. Based on these results, a control system for correcting intracavity tilt aberrations is established, and the aberration-corrected results are presented.
The influence on outcoupled mode by introducing intracavity tilt-perturbation in confocal unstable resonator is analyzed. The intracavity mode properties and Zernike-aberration coefficient of intrcavity mirror's maladjustment are calculated theoretically. The experimental results about the relations of intracavity mirror maladjustment and the properties of mode aberration are presented by adopting Hartmann-Shack wavefront sensor. The results show that the intracavity perturbation of the concave mirror has more remarkable effect on outcoupled beam-quality than that of the convex mirror. For large Fresnel-number resonator, the tilt angle of intracavity mirror has a close linear relationship with extracavity Zernike tilt coefficient. The ratio of tilt aberration coefficient approaches to the magnification of unstable resonator if equivalent perturbation is applied to concave mirror and convex mirror respectively. Furthermore, astigmatism and defocus aberration also increase with the augment of tilt aberration of beam mode. So intracavity phase-corrected elements used in unstable resonator should be close to the concave mirror. Based these results, a set of automatic control system of intracavity tilt aberration is established and the aberration-corrected results are presented and analyzed in detail.
Intracavity adaptive optics has been successfully used in solid state lasers to improve output laser beam quality. However, In order to utilize this technology to improve the output laser beam quality successfully, the distribution characteristics of phase aberration in the laser resonator should firstly be known. Thus, a set of Hartmann- Shack wave front sensor (HSWFS) to measure the time and space characteristics of phase aberration in a diode-side-pumped Nd:YAG laser was set up. In this paper, the HSWFS is briefly introduced. The experimental results for measurement of the phase aberration in a diode side-pumped Nd:YAG laser are presented. The experimental results show that, the main phase aberration in the resonator is generated by the Nd:YAG rod. The phase aberration induced by thermal deformation in the cavity mirrors is minor. The temporal behavior of phase aberration in the resonator and from cavity mirrors under light heating was also obtained.
An innovative experimental method for studying the influence of supersonic flow on laser beam transmitting has been proposed. The wavefront phase properties and the dynamic wavefront change of laser beam traversing supersonic flow can be detected by Hartmann-Shack (H-S) wavefront sensor. Beam aberrations are constructed by adopting Zernike mode-reconstruction theory. The centroid change of laser beam and the far-field properties can be obtained by further analyzing the experimental data. In the paper, the experimental principle is presented, and wavefront aberrations with several different flow parameters are given. Some beam-quality criteria such as Zernike aberration coefficient, PV and RMS value, circle energy, Strehl ratio, and centroid change of beam, are also calculated. Experimental results show that the stage of flow establishing, stabilizing and ending can be detected by using H-S wavefront sensor. By comparing the result of no flow with that of a given-parameter flow, defocus and astigmatism aberration increase obviously. At the same time, the Strehl ratio is reduced and the beam quality is degraded. The same conclusion can be obtained by comparing no test-model with the given-structural test-mode in same flow. Moreover, the wavefront aberration of laser beam in the condition of different flow parameters can also be measured and compared accurately by using the test method.
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