Evaluation Of Beam Characteristics Of High Power Semiconductor Laser

In order to improve the beam quality of wide stripe high power semiconductor laser,a beam quality measurement setup for high power semiconductor lasers is constructed basing on the strict second moment theory.This setup is used to measure the beam waist position,beam waist size and far field divergence angle of 976nm wide stripe high power semiconductor lasers prepared by our lab.The experimental result shows that with the increase of current from 1A to 10A,the fast axis beam width and far-field divergence angle increase slightly due to the anti-guidance effect,but the beam parameters change very small because of the strong refractive index guidance mechanism in the vertical direction.The beam quality is almost unchanged when the beam quality factor M~2 is only increased from1.32 to 1.48.In slow axis direction,the beam width and far field divergence angle increase gradually with the increase of operating current due to the high-order mode lasing caused by the anti-guidance effect and the thermal lens effect.The beam quality becomes worse when the beam quality factor M~2 is increased from 5.44 to 11.76.The difference of the beam quality factor is compared with the definition of paraxial beam and non-paraxial beam.The results shows that there is an obvious difference by different beam definitions in the fast axis direction and the paraxial beam definition is not suitable for the calculation.In the direction of slow axis,the results are approximately equal and can be approximately calculated by using the paraxial beam definition.In addition,it contrasts and testes the beam property of two different kinds of stripe width’s wide stripe semiconductor laser of 915 nm wavelength in the direction of slow axis.The experimental results show that the laser with wide strip width has larger active area,smaller thermal resistance,smaller junction temperature rise range and smaller red shift quantity of output wavelength.However wide stripe width makes the waist wide get larger,while the stripe width still has an effect on the far-field divergence angle,but its overall change is not obvious and it makes wide strip width laser have a poor beam quality eventually.Meanwhile the beam property of the semiconductor laser with the wavelength of 915nm and the stripe width of 180 microns is tested under different pulse operating conditions.The experimental results show that both duty ratio and the increase of pulse width can make the temperature of the active region rise,the non-uniformity of the temperature inside the laser increase and the output wavelength get a red shift,which reduces the refractive index of the active region and changes the gain distribution of the laser at the same time.The laser is more likely to occur the high-order mode lasing and the beam quality becomes worse.