Properties Study Of The Detection And Compensation Of The Low Order Aberration In The Unstable Resonator

The technical research and application about the high energy solid-state laser(HESSL)systems become hotter with the development of the bumping and the adaptive optics.Due to the thermal effect of optical device,the gain medium got a optical distortion witch has a significant impact on the output power and beam quality of unstable resonator when solid laser system is working.The technology of adaptive optics applied in unstable resonator laser is an effective measure to achieve high output beam quality.This paper is based on multi connected thin-disk laser with unstable resonator,researched the characteristics of optical distortion caused by Nd:YAG gain medium and its effect on output beam optical characteristics of unstable resonator,focusing on the correction of low order aberration in resonator.The wavefront aberration of the gain medium was direct measured by the experimental measurement method,in which the tilt aberration and defocus aberration were larger.The influence of aberration on the output beam of the laser is analyzed by numerical simulation.It is found that the tilt aberration and the defocus aberration have a significant effect on the intensity distribution of the output beam.When the pitch is about 40 micro radians,the phase distribution of the beam is seriously tilted,The output beam PV value reaches 78?m,the RMS is 16.87?m,the output optical power drops more than 50%,and even the unstable cavity can not work,therefore,in the cavity aberration correction process,the tilt aberration should be corrected firstly.The tilt aberration in the unstable resonator mainly affects two parameters:optical axis offset and pupil offset.One single optical axis deviation transmitted through the unstable resonator could make the measurement and characterization particularly difficult.In the solid-state laser resonator,it is more difficult to detect and characterize the optical axis offset within the system due to the existence of the gain media aberration.In this paper,a collimated beam is used as the reference light which transmit one round trip in the resonator and it's aberration is detected by the Hartmann-Shack wavefront Sensor replacing the wavefront distortion of the main laser in the resonator.An optical mirror is used to correct the tilt aberration and the structure is simple and easy to use.Compared the correction method based on the one-way measurement with the correction effect based on the round trip detection method,the inclination aberration is introduced in the unstable cavity,and the output power is only 63.4%of the ideal output power when no correction measures are taken.Based on the round trip detection and correction method can completely correct the cavity tilt aberration,the laser output power to upgrade to 99.11%of the ideal output power.In the experiment,the tilt aberration,the defocus aberration and the high order aberration were corrected by the electromagnet mirror and the deformable mirror respectively.The laser was stable in the closed state of the optical axis correcting system,the output of the laser was stable,the power reached 4358.89w,The laser output power is increased by 24%and the output beam quality is improved greatly,which verifies the feasibility of the calibration strategy.