Realization of Tiled-Grating Compressors for the OMEGA EP Petawatt-Class Laser System

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1 Realization of Tiled-Grating Compressors for the OMEGA EP Petawatt-Class Laser System 1.41 m.43 m J. Qiao et al. University of Rochester Laboratory for Laser Energetics CLEO/QELS 28 San Jose, CA 4 9 May 28

2 Summary Two large-scale tiled-grating compressors have been activated for the OMEGA EP Petawatt-Class Laser System Eight tiled-grating assemblies (TGA s) have been built, tiled, and demonstrated submicroradian stability. The automatic tiling processes for aligning individual TGA s and optimizing overall tiling performance have been implemented. Two tiled-grating compressors have been integrated and activated. Tiling did not degrade focal-spot performance. Both compressors achieved subpicosecond-pulse durations. G822

3 Collaborators A. Kalb J. H. Kelly D. Canning T. Nguyen J. Bunkenburg Laboratory for Laser Energetics University of Rochester

4 OMEGA EP requires two tiled-grating compressor systems to meet energy and focal-spot requirements OMEGA EP requirement Energy-on-target: 2.6 kj Pulse width: 1 to 1 ps Stretcher Amplifiers Grating 3 Compressor with tiled gratings Grating 2 Grating 4 Grating 1 Beam size on gratings: 1.23 m on G1 and G4; 1.28 m on G2 and G3; size of individual gratings:.47 m #.43 m Three tiles are interferometrically aligned to generate a 1.5-meter-sized grating. G8221 D. Strickland and G. Mourou, Opt. Commun. 56, 219 (1985). L. J. Waxer, CLEO 28, Paper JThB1.

The grating compressor chamber (GCC) has been integrated, aligned, and activated 4.6 21.

6 m Vacuum-compatible DM Beam combiner Short-pulse diagnostic package Beam combiner m Deformable

5 The grating compressor chamber (GCC) has been integrated, aligned, and activated m Upper-compressor view Four tiled-grating assemblies (TGA s) Fizeau tiling interferometer 4.6 m Vacuum-compatible DM Beam combiner Short-pulse diagnostic package Beam combiner m Deformable mirror TGA4 TGA3 Fizeau reflection flat Short-pulse diagnostic path G8222 TGA1 TGA2 Fizeau transmission flat

6 Each TGA is tiled using an interferometric technique inside the grating compressor chamber at vacuum IR cw laser Fizeau nearfield camera Reflection flat (RF) TGA2 TGA1 TGA4 TGA3 Selection mirror Transmission flat (TF) Compressor alignment performed using only single central tiles A built-in Fizeau interferometer is used to tile each individual TGA G8225 TGA, selection mirror, and reflection mirror are rotated to align each outboard tile relative to the central tile Near-field tiling is realized using an interference pattern formed by the reference beam from the TF and the testing beam from two adjacent tiles and the RF.

Fourier fringe analysis is used to tile each individual TGA Interferogram

signal FFT Filtering IFFT Calculate relative tilt, tip to the TF; recover

4984 m Outboard tile Central tile Wavefront of the two tiles 3 2 1 8 6 x (mm)

7 Fourier fringe analysis is used to tile each individual TGA Interferogram near field Fourier transform of the interferogram Filtered first harmonic signal FFT Filtering IFFT Calculate relative tilt, tip to the TF; recover phase rms =.4984 m Outboard tile Central tile Wavefront of the two tiles x (mm) y (mm) G8226 J. Qiao et al., Opt. Express 15, 9562 (27). M. Takeda, H. Ina, and S. Kobayshi, J. Opt. Soc. Am. 72, 156 (1982).

8 Eight OMEGA EP production TGA s have been successfully tiled rms wavefront (m) Tiled rms wavefront for eight TGA s TGA number rms wavefront (m) Stability of the tiled wavefront (TGA5) Mean rms =.8 m STD rms =.3 m Time (h) All eight TGA s have been tiled and tested outside the GCC before being installed G8227 Each TGA was tiled for its GCC use configuration using a 24-in. Fizeau interferometer The tiled wavefronts of all qualified TGA s maintained for at least 12 h All eight TGA s have been retiled in the GCC at vacuum Tiled positions are maintained by closing the actuator control loop with feedback of position-displacement sensors. Submicroradian angular stability is achieved

9 The final tiling performance is optimized using a far-field method by adjusting TGA4 Optical layout for tiling optimization Single-tile configuration 2 2 All eight TGA s are rotated to the aligned compressor fx (nrad) positions after being individually tiled. Each of the two outboard tiles of TGA4 is used to remove the residual tiling errors from three other tiles of TGA1 to TGA3 corresponding to the same side of the beam. The far-field tiling-optimization process is automated. G8228 IR cw beam Apodizer array Far-field camera TGA2 Retro mirror #2 for final tiling optimization Two-tile configuration TGA1 TGA4 Triple-tile configuration TGA3 Retro mirror #1 for tiling beam calibration Optimized far-field spot fy (nrad) 2 2 Far field of triple tile compressor Steering mirror to target chambers

The triple-tile compressor offers a tighter focal spot than the sub-aperture single-central-tile compressor fy (nrad) Normalized intensity G8229 Far field of single-centraltile compressor 3 2 3 1 1 2

10 The triple-tile compressor offers a tighter focal spot than the sub-aperture single-central-tile compressor fy (nrad) Normalized intensity G8229 Far field of single-centraltile compressor fx (nrad) Comparison between the two X lineouts 1. FWHM:.8 Single X = nrad Triple X = nrad.2. 5 fx (nrad) Far field of tripletile compressor 2 2 fx (nrad) Comparison between the two Y lineouts 5 fy (nrad) FWHM: Single Y = 3. nrad Triple Y = 3.1 nrad Far field was measured for both single-centraltile and triple-tile configurations FWHM ratio: X lineouts = 3:1 Y lineouts = 1:1 The triple-tile compressor delivered a tighter farfield spot than the singlecentral-tile configuration. No degradation of spatial properties due to tiling

11 Subpicosecond pulses are obtained with the two tiled-grating compressors Normalized intensity Auto-correlation scanning result for the lower compressor Transform limit Triple tile Single tile Auto-correlation scanning result for the upper compressor Time (ps) Time (ps) LC (fs) UC (fs) Single tile 63 6 Triple tile 63 6 Transform limit 4 41 Decorrelated pulse width of the two compressors are obtained (decorrelation factor = 1.34) Subpicosecond pulses obtained on both compressors No degradation of temporal properties due to tiling. G823

12 Summary/Conclusions Two large-scale tiled-grating compressors have been activated for the OMEGA EP Petawatt-Class Laser System Eight tiled-grating assemblies (TGA s) have been built, tiled, and demonstrated submicroradian stability. The automatic tiling processes for aligning individual TGA s and optimizing overall tiling performance have been implemented. Two tiled-grating compressors have been integrated and activated. Tiling did not degrade focal-spot performance. Both compressors achieved subpicosecond-pulse durations. G822

Demonstration of Real-Time, Phase-Locked Alignment of Tiled Gratings for Chirped-Pulse Amplified Lasers

Demonstration of Real-Time, Phase-Locked Alignment of Tiled Gratings for Chirped-Pulse Amplified Lasers Introduction The OMEGA EP (extended performance) petawatt, multikilojoule, solid-state laser, presently