The chirped-pulse amplification system plays a critical role in the process of achieving high-peak ultrashort pulses. Chirped-pulse amplification technology performance mainly depends on the pulse compression gratings. Diffraction efficiency is the critical parameter of the pulse compression gratings, and optimization of grating shape can achieve higher diffraction efficiency. If the photoresist grating mask bottom is not clean, the side walls would not be steep and duty cycle would be too big or too small, thus pulse compression grating diffraction efficiency would decrease. Solving these problems is the key to improve the diffraction efficiency. In this paper, oxygen etching methods are used to reduce the photoresist mask duty cycle, and PDMS pressing method is used to increase the duty cycle of photoresist mask, and aperture up to 100 mm×100 mm. Best photoresist grating mask parameter could be obtained by effectively combining the above two methods. Based on above techniques, a number of pulse compression gratings with line densities of 1740 lines∕mm was achieved. The diffraction efficiency at the-1st order was greater than 99% for TE polarized light. A qualitative judgments for graphic transfer of ion beam etching is received through the picture before and after etching which is get from the SEM. These experimental results proved the accuracy, stability, and success rates of the technique.
Fabrication and testing results of sine-top, high-efficiency, broadband gold-coated gratings (BGCG) for high-power laser pulse compression applications are reported. These gratings differ from conventional metal-on-photoresist pulse compression gratings in that the gratings patterns are generated by directly etching the quartz substrate. The groove depth and duty cycle of the photoresist mask was controlled by changing photoresist thickness and adjusting exposure and development times, respectively. The duty cycle of the photoresist mask was further corrected by oxygen plasma etching. Using this method, high efficiency, sine-top, BGCG with line densities of 1740 lines/mm was achieved. The average diffraction efficiency at the-1st order was 89.2% and the peak value was 90% for TM polarized light as the wavelength increases from 750 to 850 nm.
Broadband gold-coated grating (BGCG) is one of the key elements of large pulse compression systems. Compared with
other pulse compression grating (PCG), BGCG have the advantages of simple structure and low cost etc. More
importantly, this kind of grating can get high diffraction efficiency within a broadband range (usually 200 nm or more).
In this paper the authors report a process for fabrication of sine-top BGCG. When gratings are intended for use with
high-power lasers, their laser-damage threshold has an importance equal to that of the diffraction efficiency. These
gratings fabricated by this method differ from conventional metal-on-photoresist PCGs in that the gratings patterns are
generated by etching the fused silica substrate directly. This can improve the laser damage threshold. The groove depth
and duty cycle of the photoresist mask were controlled by changing photoresist thickness and adjusting exposure and
development time. The duty cycle of the fused silica grating was further corrected by oxygen plasma etching. Using this
method, high efficiency sine-top BGCGs with line densities of 1740 lines /mm have been achieved, this paper has a good
reference value to the further fabrication of larger aperture gold-coated PCG.