Effect of wavefront distortion on focusing performance of long-focal-depth mirror

Abstract A long-focal-depth mirror can produce a quasi-Bessel beam, which has the advantages of a long focal depth, a small spot, independence of wavelength, and a uniform longitudinal intensity. The laser beam emitted by a laser has a certain wavefront distortion, and real optical elements will also produce extra aberrations in the process of processing and assembling, which will then introduce new wavefront distortion to the optical system. Wavefront distortion will affect the phase and then affect the coherence and beam quality of the laser beam, ultimately affecting the beam focusing performance. To accurately study the effect of wavefront distortion on the focusing performances of long-focal-depth mirrors, an aberration model based on Zernike polynomials was established. Based on scalar diffraction theory, the effects of three typical aberrations on the focusing performances of long-focal-depth mirrors were calculated. The focusing performances were comprehensively evaluated by using various evaluation manners, including the power in the bucket. The calculation results showed that, compared with the ideal state, for an astigmatism or coma with a root mean square (RMS) more than 0.25 μ m, the focusing performance of the long-focal-depth mirror dropped abruptly. The focused spot calculated with a 0.10 μ m aberration shows a distribution identical to that when the component is properly clamped, exhibiting no significant aberration features, indicating that a RMS of 0.10 μ m is acceptable.