Evaluation of femtosecond laser damage to gold pulse compression gratings fabricated by magnetron sputtering and e-beam evaporation.

ABSTRACT

In this study, two kinds of Au-coated gratings (ACGs) with a period of 1740 lines/mm were fabricated and evaluated. For these ACG samples, magnetron sputtering and e-beam evaporation were used as the gold deposition process, and the samples had a bandwidth of at least 170 nm, with the -1st-order diffraction efficiency exceeding 90% around the center wavelength of 800 nm. The one-on-one damage threshold of ACGs fabricated by magnetron sputtering and e-beam evaporation measured at a pulse width of 60 fs was 0.59 J/cm2 and 0.43 J/cm2 in the case of the beam normal fluence, respectively. The typical damage morphology of the former type of samples was melting of the gold film, whereas those of the latter type were blisters and peeling off of the gold film. In theory, the electromagnetic field, temperature field, and thermal stress field distribution in the ACGs were calculated using the finite element method. We demonstrated that the adhesion between the gold film and the photoresist played an important role in determining the damage behavior. Thus, the laser resistance of ACG can be improved by enhancing the adhesion between the gold film and the photoresist, and magnetron sputtering was an alternative method to obtain ACGs with much better adhesion.