Laser Damage Resistant MLD Gratings
 
Summaries of Selected Research Activities:
Liquid Crystal Optics for High Power Lasers
Laser Damage Resistant MLD Gratings
Polymer Cholestric Liquid
Crystal Flakes
Optical Polishing Pitch
Bound Abrasive Polishers
Magnetorheological Finishing (MRF)
MRF of KDP
MRF of Sapphire
MRF of Optical Polymers
MRF of CVD ZnS
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The OMEGA EP laser uses pulse compression to generate 10-ps laser beams for experiments near the petawatt level. Laser-matter interactions may be studied in a vacuum chamber in the OMEGA EP laser bay, or in conjunction with the 60-beam OMEGA laser in the OMEGA target chamber.

4 beamline Nd:glass OMEGA EP Laser System. The grating compression chamber (GCC) w/ door open is at the top center of this photograph

 

Fundamental to the generation and propagation of these short pulses are a series of 24 large diffractive optical elements on fused silica plates, 47-cm wide by 47-cm tall by 10-cm thick, that perform the compression operation on two EP 1054-nm beams. They are located in a large vacuum chamber call the GCC.

Upper beamline in OMEGA EP grating compression chamber

Three gratings are "tiled" together to form one large diffractive optic

 

Each grating consists of a fine linear array of silica pillars and grooves with a density of 1740 lines per mm, located on the flat surface of a multilayer dielectric (MLD) thin film coating.To manufacture these MLD diffraction gratings, interference lithography is employed to create the diffraction pattern in photoresist, followed by ion beam etching of the pattern into a silica layer on top of the MLD.

 

 

Edge-on SEM view of grating and the MLD beneath

 

MLD grating pillars

(Ashe et al., 2007)

 

Interference lithography is a "dirty" business, and  degree to which the lithography debris can be cleaned off of the grating determines how well the structure performs and survives upon exposure to the EP laser beam.Research in our group is directed toward chemical cleaning of grating surfaces to remove contaminants and increase performance.

 

Pie-shaped segments of MLD grating. The uncleaned segment is discolored; the cleaned segment is less colored.

Flowchart for an advanced MLD grating cleaning process conducted near room temperature.

 

 

 

 

 

 

 

 

 

 

 

 

 

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