James D. Nissen

Picosecond laser damage performance assessment of multilayer dielectric gratings in vacuum

Precise assessment of the high fluence performance of pulse compressor gratings is necessary to determine the safe operational limits of short-pulse high energy lasers. We have measured the picosecond laser damage behavior of multilayer dielectric (MLD) diffraction gratings used in the compression of chirped pulses on the Advanced Radiographic Capability (ARC) kilojoule petawatt laser system at the Lawrence Livermore National Laboratory (LLNL). We present optical damage density measurements of MLD gratings using the raster scan method in order to estimate operational performance. We also report results of R-on-1 tests performed with varying pulse duration (1-30 ps) in air, and clean vacuum. Measurements were also performed in vacuum with controlled exposure to organic contamination to simulate the grating use environment. Results show sparse defects with lower damage resistance which were not detected by small-area damage test methods.

Precise diffraction efficiency measurements of large-area greater-than-99%-efficient dielectric gratings at the Littrow angle

We have developed improved cavity-finesse methods for characterizing the diffraction efficiencies of large gratings at the Littrow angle. These methods include measuring cavity length with optical techniques, using a Michelson interferometer to calibrate piezoelectric transducer nonlinearities and angle-tuning procedures to confirm optimal alignment. We used these methods to characterize two 20 cm scale dielectric gratings. The values taken from across their surfaces collectively had means and standard deviations of micro=99.293% and sigma=0.164% and micro=99.084% and sigma=0.079%. The greatest efficiency observed at a single point on a grating was (99.577+/-0.002)%, which is also the most accurate measurement of the diffraction efficiency in the literature of which we are aware. These results prove that a high diffraction efficiency with low variation is achievable across large apertures for gratings.

Performance measurements of the injection laser system configured for picosecond scale advanced radiographic capability

We have characterized the Advanced Radiographic Capability injection laser system and demonstrated that it meets performance requirements for upcoming National Ignition Facility fusion experiments. Pulse compression was achieved with a scaled down replica of the meter-scale grating ARC compressor and sub-ps pulse duration was demonstrated at the Joule-level.

Gratings for High-Energy Petawatt Lasers

To enable high-energy petawatt laser operation we have developed the processing methods and tooling that produced both the worlds largest multilayer dielectric reflection grating and the worlds highest laser damage resistant gratings. We have successfully delivered the first ever 80 cm aperture multilayer dielectric grating to LLNLs Titan Intense Short Pulse Laser Facility. We report on the design, fabrication and characterization of multilayer dielectric diffraction gratings.

Diffraction grating eigenvector for translational and rotational motion

Future energy scaling of high-energy chirped-pulse amplification systems will benefit from the capability to coherently tile diffraction gratings into larger apertures. Design and operation of a novel, accurate alignment diagnostic for coherently tiled diffraction gratings is required for successful implementation of this technique. An invariant diffraction direction and phase for special moves of a diffraction grating is discussed, allowing simplification in the design of the coherently tiled grating diagnostic. An analytical proof of the existence of a unique diffraction grating eigenvector for translational and rotational motion that conserves the diffraction direction and diffracted wave phase is presented.

Advanced dielectric grating technology for high-energy petawatt lasers

We describe the design, fabrication, and test of large-area multilayer dielectric gratings for high-energy petawatt lasers. 80/spl times/40-cm/sup 2/, 1780-mm/sup -1/ gratings have been fabricated, exhibiting high diffraction efficiency and >4 J/cm/sup 2/, 10-ps damage thresholds on witness samples.

Optical damage performance measurements of multilayer dielectric gratings for high energy short pulse lasers

We investigate the laser damage resistance of multilayer dielectric (MLD) diffraction gratings used in the pulse compressors for high energy, high peak power laser systems such as the Advanced Radiographic Capability (ARC) Petawatt laser on the National Ignition Facility (NIF). Our study includes measurements of damage threshold and damage density (ρ(Φ)) with picosecond laser pulses at 1053 nm under relevant operational conditions. Initial results indicate that sparse defects present on the optic surface from the manufacturing processes are responsible for damage initiation at laser fluences below the damage threshold indicated by the standard R-on-1 test methods, as is the case for laser damage with nanosecond pulse durations. As such, this study supports the development of damage density measurements for more accurate predictions on the damage performance of large area optics.

Dispersion balancing of complex CPA-systems using the phase-shifting technique

Dispersion balancing in complex, high-intensity, chirped-pulse-amplification, laser systems is critical for optimizing temporal pulse fidelity. We demonstrate a method for dispersion management of the eight-beam, Petawatt Advanced Radiographic Capability Laser being built at the National Ignition Facility utilizing the phase shift technique.

Characterization of Polarization Sensitive, High Efficiency Dielectric Gratings for Formation Flight Interferometry

Reflective diffraction gratings enable novel optical configurations that simplify and improve laser interferometers. We have proposed an all-reflective grating interferometer that can be used in LISA type interferometers for space gravitational wave detection [1]. One configuration requires a highly polarization sensitive grating. We report on characterizations of a grating made atop high reflective dielectric layers. Using a direct measurement method, the diffraction efficiency at the Littrow angle for s-polarization is measured as 97.3% and for p-polarization 4.2%, leading to a s/p polarization diffraction ratio of 23.2. The depolarization from s- to p-polarization is measured to be ~1.7×10-4, and from p- to s-polarization 1.8×10-4. We derived a transfer matrix based on these measurements. Furthermore, we have developed a more accurate method for diffraction efficiency measurement using a grating cavity. These measurements are encouraging steps taken towards the requirements of an ideal grating interferometer.

Group delay measurement for balancing dispersion in complex stretcher-compressor systems

The phase-shift technique for measuring group-delay has novel applications for aligning and commissioning grating compressors and balancing dispersion in large, high-energy petawatt and other complex, chirped-pulse amplifier systems.