Post-processing method to enhance the damage threshold of fused quartz optical element

The invention discloses a post-processing method to enhance the damage threshold of a fused quartz optical element. First, a fluorescence confocal microtechnique is employed to detect the distribution scope and scale of subsurface defects of the fused quartz optical element; and multi-frequency ultrasonic alternating multiplexing assisted chemical etching technique through KHz and MHz frequencies is used for etching different depths according to subsurface defects in different depth distribution; different frequencies are used for different scales of subsurface defects to peel off the subsurface defects layer by layer, in order to enhance the damage threshold. The post-processing method has global processing capability on optical element; hydrofluoric acid corrosion treatment completely removes a polishing deposited layer to expose the scratches on the subsurface damage layer, and sharp new look of the scratches are well passivated; the introduction of multi-frequency ultrasonic / megasonic assist can act on scratch passivation at different scales to prevent re-deposition of the etching reaction byproducts and improve the process stability. The method can stably and greatly enhance the damage threshold of the fused quartz optical element.