A Scalable Design for a High Energy, High Repetition Rate, Diode-Pumped Solid State Laser (DPSSL) Am...
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A Scalable Design for a High Energy, High Repetition Rate, Diode-Pumped Solid State Laser (DPSSL) Amplifier. Paul Mason, Klaus Ertel, Saumyabrata Banerjee, Jonathan Phillips, Cristina Hernandez-Gomez, John Collier Workshop on Petawatt Lasers at Hard X-Ray Light Sources

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Motivation

A Scalable Design for a High Energy, High Repetition Rate, Diode-Pumped Solid State Laser (DPSSL) Amplifier

Paul Mason, Klaus Ertel, Saumyabrata Banerjee, Jonathan Phillips, Cristina Hernandez-Gomez, John Collier

Workshop on Petawatt Lasers at Hard X-Ray Light Sources

5-9th September 2011, Dresden, Germany

[email protected]

STFC Rutherford Appleton Laboratory,

Centre for Advanced Laser Technology and Applications

R1 2.62 Central Laser Facility, OX11 0QX, UK

+44 (0)1235 778301


Motivation

Motivation

  • Next generation of high-energy PW-class lasers

    • Multi-J to kJ pulse energy

    • Multi-Hz repetition rate

    • Multi-% wall-plug efficiency

  • Exploitation

    • Ultra-intense light-matter interactions

    • Particle acceleration

    • Inertial confinement fusion

  • High-energy DPSSL amplifiers needed

    • Pumping fs-OPCPA or Ti:S amplifiers

    • Drive laser for ICF

    • Pump technology for HELMHOLTZ-BEAMLINE

BeamlineFacility

  • HELMHOLTZ- BEAMLINE


Motivation

Amplifier Design Considerations

  • Requirements

    • Pulses from 10’s J to 1 kJ, 1 to 10 Hz, few ns duration, efficiency 1 to 10%

  • Gain Medium

    • Ceramic Yb:YAG down-selected as medium of choice

  • Amplifier Geometry


Motivation

STFC Amplifier Concept

~175K

  • Diode-pumped multi-slab amplifier

    • Ceramic Yb:YAG gain medium

    • Co-sintered absorber cladding for ASE suppression

  • Distributed face-cooling by stream of cold He gas

    • Heat flow along beam direction

    • Low overall aspect ratio & high surface area

  • Operation at cryogenic temperatures

    • Higher o-o efficiency – reduction of re-absorption

    • Increased gain cross-section

    • Better thermo-optical & thermo-mechanical properties

  • Graded doping profile

    • Equalised heat load in each slab

    • Reduces overall thickness (up to factor of ~2)


Motivation

Modelling

Cr4+:YAG

50%

pump region

  • Laser physics

    • Assumptions

      • Target output fluence 5 J/cm²

      • Pump 940 nm, laser 1030 nm

    • Efficiency & gain

      • Optimum doping x length product for maximum storage ~ 50%

      • Optimum aspect ratio to minimise risk of ASE (g0D < 3) of ~1.5

    • Extraction

      • Extraction efficiency ~ 50%

  • Thermal & fluid mechanics

    • Temperature distribution

    • Stress analysis

    • Optimised He flow conditions

3.8

Yb:YAG


Motivation

Scalable Design


Motivation

DiPOLE Prototype Amplifier

  • Design sized for ~ 10 J @ 10 Hz

  • Aims

    • Validate & calibrate numerical models

    • Quantify ASE losses

    • Test cryogenic gas-cooling technology

    • Test (other) ceramic gain media

    • Demonstrate viability of concept

  • Progress to date

    • Cryogenic gas-cooling system commissioned

    • Amplifier head, diode pump lasers & front-end installed

    • Full multi-pass relay-imaging extraction architecture under construction

    • Initial pulse amplification tests underway

Ceramic YAG disk with absorber cladding

Yb3+

Cr4+

Diode pump laser


Motivation

Optical Gain Material

Cr4+

Pump2 x 2

cm²

  • 4 x co-sintered ceramic Yb:YAG disks

    • Circular 55 mm diameter x 5 mm thick

    • Cr4+ absorbing cladding

    • Two doping concentrations (1.1 & 2.0 at.%)

55 mm

35 mm

Yb3+

Fresnel limit ~84%

PV

0.123

wave

1030 nm

940 nm


Motivation

Amplifier Head Design

  • Schematic

  • CFD modelling

Disks

Uniform T across pumped region ~ 3K

Pump

Pump

He flow

pressure

windows

Vacuum

vacuum

windows

He flow

40 m3/hr ~ 25 m/s @ 10 bar, 175 K


Motivation

Diode Pump Laser

  • Built by Consortium

    • Ingeneric, Amtron & Jenoptic

  • Two systems supplied

    • 0 = 939 nm, FWHM < 6 nm

    • Peak power 20 kW, 0.1 to 10 Hz

    • Pulse duration 0.2 to 1.2 ms

    • Uniform square intensity profile

      • Steep well defined edges

    • ~ 80 % spectral power within  3 nm

      • Good match to Yb:YAG absorptionspectrum @ 175K

Measured

20 mm

20 mm


Motivation

DiPOLE Laboratory

Cryo-cooling system

Amplifier head

2 x 20 kW diode pump lasers


Motivation

Front-end Injection Seed

Amplifier crystal

nsecoscillator

  • Free-space diode-pumped MOPA design

    • Built by Mathias Siebold’s team @ HZDR Germany

  • Cavity-dumped Yb:glass oscillator

    • Tuneable 1020 to 1040 nm

      •  ~ 0.2 nm

    • Fixed temporal profile

      • Duration 5 to 10 ns

    • PRF up to 10 Hz

    • Output energy up to 300 µJ

  • Multi-pass Yb:YAG boosteramplifier

    • 6 or 8 pass configuration

    • Output energy ~ 100 mJ

Booster pump diode

x3 or x4

Polarisation switching waveplate

100 mJ

output


Motivation

Initial Pulse Amplification Results

  • Simple bow tie extraction architecture

    • 1, 2 or 3 passes

    • Limited by diffraction effects

  • Injection seed

    • Gaussian beam expanded to overfill pump region

    • Energy ~ 60 mJ

Seed

Amplified

beam

Pump

Pump


Motivation

Spatial Beam Profiles @ 100K, 1 Hz

Gain  8

Gain  6

E = 2.6 J @ 10 Hz


Motivation

Pulse Energy v. Pump Pulse Duration

Onset of ASE loss

  • 3 passes @ 1 Hz

  • Relay-imaging multi (6 to 8) pass extraction architecture is required to allow >10 J energy extraction at 175K

5.9 J


Motivation

Conclusions

  • Cryogenic gas cooled Yb:YAG amplifier offers potential for efficient, high energy, high repetition rate operation

    • At least 25% optical-to-optical efficiency predicted

  • Proposed multi-slab architecture should be scalable toat least 1 kJ generating ns pulses at up to 10 Hz

    • Limit to scaling is acceptable B-integral

  • DiPOLE prototype amplifier shows very promising results

    • Installation of relay-imaging multi-pass should deliver 10 J @ 10 Hz

  • Strong candidate pump technology for generating high energy, ns pulses at ~ 1 Hz for HELMHOLTZ-BEAMLINE


Motivation

Thank you for your attention!

Any Questions?


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