Color separation gratings for diverting the unconverted light away from the NIF target

Technical Report · Tue Mar 11 04:00:00 EST 1997

DOI:https://doi.org/10.2172/562816· OSTI ID:562816

Dixit, S N; Rushford, M C; Thomas, I M; Herman, S M; Britten, J A; Shore, B W; Perry, M D

Most of the glass laser based inertial confinement fusion systems around the world today employ non-linear frequency conversion for converting the 1.053 micrometer light at the fundamental frequency (referred to as 1{omega} light) to either its second harmonic (called 2{omega}) at 527 nm or to its third harmonic (called 3{omega}) at 351 nm. Shorter wavelengths are preferred for laser fusion because of the improved coupling of the laser light to the fusion targets due to reduced fast electron production at shorter wavelengths. The frequency conversion process, however, is only about 60-70% efficient and the residual 30-40% of the energy remains at 1{omega} and 2{omega} frequencies. Color separation gratings (CSGs) offer a versatile approach to reducing and possibly eliminating the unconverted light at the target region. A CSG consists of a three- level lamellar grating designed so that nearly all of the 3{omega} light passes through undiffracted while the residual 1{omega} and 2{omega} energy is diverted into higher diffraction orders. The diffraction angle is determined solely by the grating period. We have demonstrated the concept of using a color separation grating. We fabricated a 345 micrometer period CSG in fused silica using lithographic processes and wet etching. The measured far field indicates that greater than 95% of the incident light is preserved in the 3{omega} zeroth order while less than 5% of unconverted 1{omega} and 2{omega} light is remaining in the zeroth order. We would like to add that diffractive optics fabricated in fused silica by wet etching in hydrofluoric acid should have high damage threshold. Our experience suggests that the damage threshold of the etched substrate is at least as high as the unetched part. 6 refs., 4 figs., 1 tab.

• Research Organization: Lawrence Livermore National Lab., CA (United States)
• Sponsoring Organization: USDOE, Washington, DC (United States)
• DOE Contract Number: W-7405-ENG-48
• OSTI ID: 562816
• Report Number(s): UCRL-JC--124512; CONF-9610225--41; ON: DE97053415
• Country of Publication: United States
• Language: English

Related Subjects

70 PLASMA PHYSICS AND FUSION TECHNOLOGY
DIFFRACTION GRATINGS
EXPERIMENTAL DATA
FABRICATION
PERFORMANCE TESTING
US NATIONAL IGNITION FACILITY