Public Abstract

DE-SC0019496: High-Average-Power (HAP) Thermal Management for Ultrafast Lasers

Award Status: Inactive

Institution: University of Rochester, Rochester, NY
UEI: F27KDXZMF9Y8
DUNS: 041294109

Most Recent Award Date: 10/26/2021
Number of Support Periods: 3
PM: Colby, Eric

Current Budget Period: 09/25/2020 - 12/31/2021
Current Project Period: 09/25/2018 - 12/31/2021
PI: Zuegel, Jonathan

Supplement Budget Period: N/A

Public Abstract

High-Average-Power (HAP) Thermal Management for Ultrafast Lasers Jonathan D. Zuegel, Univ. of Rochester/Laboratory for Laser Energetics (Principal Investigator) Jake Bromage and Erik Power, Univ. of Rochester/Laboratory for Laser Energetics (Co-Investigators) Peter Moulton and T. Y. Fan, MIT Lincoln Laboratory (Co-Investigators) Chirped-pulse amplification (CPA) represents the most mature technical approach to realize high-energy, femtosecond lasers at high average power (HAP) for laser-plasma wakefield acceleration, x-ray generation through Compton Scattering, and high-repetition-rate secondary radiation sources such as high-harmonic generation. Scaling CPA to multi-kilowatt average powers with diffraction-limited performance critically depends on managing thermal loads in the diffraction gratings used for pulse compression. All HAP lasers face common challenges with diffraction grating and focal spot performance. Significantly better thermal management of diffraction gratings is needed for future HAP lasers for accelerator applications. Advanced broadband grating designs and new thermal management techniques are required to minimize thermal distortions that compromise compressor performance. The proposed research and development will develop advanced broadband gratings on novel substrates with superior thermo-mechanical properties and optimized active cooling for compact HAP laser pulse compressors. The average-power handling capacity of HAP gratings will be increased so they can be operated close to their single-pulse fluence limit. The improvement in performance enabled by advanced gratings can be quantified for a given system metric, such as beam quality or pulse compressibility, as the power density increase (PDI). Achieving high PDI values must be consistent with achieving system specifications, such as diffraction efficiency, bandwidth, and damage threshold. Three strategies will be adopted to achieve high PDI factors: 1. Develop substrates with high thermal stability (low expansion materials) and/or low thermal gradients (high thermal conductivity). Novel ceramic technology enables machining cooling channels into a thermally stable substrate. Another approach will be investigated that combines active cooling with high thermal-conductivity substrates, like silicon and silicon carbide. Actively cooled silicon grating substrates are particularly attractive since highly developed manufacturing techniques from the semiconductor industry could be employed to fabricate the grating structures and the embedded cooling structures. 2. Develop active-cooling techniques suitable for vacuum use that result in negligible wavefront “print through.” High PDI values are predicted using embedded cooling to achieve a one-dimensional heat flow perpendicular to the grating surface. Early-stage models predict wavefront print through to be up to three orders of magnitude smaller than the low-order thermal expansion of the surface, depending on substrate material. 3. Develop low-absorption gratings that meet all other primary specifications. Broadband multi-layer dielectric (MLD) gratings with low absorption are required to minimize thermal loading of gratings. Grating prototypes will be fabricated and tested at high-peak- and high-average-power densities. Test results will be used to refine models and develop full-scale grating designs for high-energy, high-average-power compressors. Integrated opto-mechanical models will be developed to simulate the impact that compressor gratings under thermal load have on ultrafast laser system performance, and optimize actively cooled substrate materials. Experiments with prototype optical components will verify opto-mechanical models suitable for system engineering. This program addresses three of the five topical areas in the Accelerator Stewardship - Ultrafast Laser Technology Program (Track 1.b): Increased robustness and reduction in size of optical components; Innovations in laser architectures, cryogenics, other advanced thermal management techniques; and Improvements in laser quality.

High-Average-Power (HAP) Thermal Management for Ultrafast Lasers

Jonathan D. Zuegel, Univ. of Rochester/Laboratory for Laser Energetics (Principal Investigator)
Jake Bromage and Erik Power, Univ. of Rochester/Laboratory for Laser Energetics (Co-Investigators)
Peter Moulton and T. Y. Fan, MIT Lincoln Laboratory (Co-Investigators)

Chirped-pulse amplification (CPA) represents the most mature technical approach to realize high-energy, femtosecond lasers at high average power (HAP) for laser-plasma wakefield acceleration, x-ray generation through Compton Scattering, and high-repetition-rate secondary radiation sources such as high-harmonic generation. Scaling CPA to multi-kilowatt average powers with diffraction-limited performance critically depends on managing thermal loads in the diffraction gratings used for pulse compression.

All HAP lasers face common challenges with diffraction grating and focal spot performance. Significantly better thermal management of diffraction gratings is needed for future HAP lasers for accelerator applications. Advanced broadband grating designs and new thermal management techniques are required to minimize thermal distortions that compromise compressor performance. The proposed research and development will develop advanced broadband gratings on novel substrates with superior thermo-mechanical properties and optimized active cooling for compact HAP laser pulse compressors.

The average-power handling capacity of HAP gratings will be increased so they can be operated close to their single-pulse fluence limit. The improvement in performance enabled by advanced gratings can be quantified for a given system metric, such as beam quality or pulse compressibility, as the power density increase (PDI). Achieving high PDI values must be consistent with achieving system specifications, such as diffraction efficiency, bandwidth, and damage threshold. Three strategies will be adopted to achieve high PDI factors:

1. Develop substrates with high thermal stability (low expansion materials) and/or low thermal gradients (high thermal conductivity). Novel ceramic technology enables machining cooling channels into a thermally stable substrate. Another approach will be investigated that combines active cooling with high thermal-conductivity substrates, like silicon and silicon carbide. Actively cooled silicon grating substrates are particularly attractive since highly developed manufacturing techniques from the semiconductor industry could be employed to fabricate the grating structures and the embedded cooling structures.

2. Develop active-cooling techniques suitable for vacuum use that result in negligible wavefront “print through.” High PDI values are predicted using embedded cooling to achieve a one-dimensional heat flow perpendicular to the grating surface. Early-stage models predict wavefront print through to be up to three orders of magnitude smaller than the low-order thermal expansion of the surface, depending on substrate material.

3. Develop low-absorption gratings that meet all other primary specifications. Broadband multi-layer dielectric (MLD) gratings with low absorption are required to minimize thermal loading of gratings.

Grating prototypes will be fabricated and tested at high-peak- and high-average-power densities. Test results will be used to refine models and develop full-scale grating designs for high-energy, high-average-power compressors. Integrated opto-mechanical models will be developed to simulate the impact that compressor gratings under thermal load have on ultrafast laser system performance, and optimize actively cooled substrate materials. Experiments with prototype optical components will verify opto-mechanical models suitable for system engineering.

This program addresses three of the five topical areas in the Accelerator Stewardship - Ultrafast Laser Technology Program (Track 1.b): Increased robustness and reduction in size of optical components; Innovations in laser architectures, cryogenics, other advanced thermal management techniques; and Improvements in laser quality.