DCS laser for Thomson scattering diagnostic applications Authors Jason Zweiback 10/6/2015 jzweiback@logostech.net 1
Summary Motivation DCS laser Laser for Thomson scattering diagnostics 2
What is the Dynamic Compression Sector? A DOE/NNSA sponsored user facility dedicated to understanding dynamic compression of condensed matter WSU/APS partnership to optimally link dynamic compression platforms to a dedicated synchrotron beamline WSU will operate the DCS as a national user facility Movies in single event experiments; APS upgrade important Examine time-dependent changes under dynamic compression Peak stresses (~1 GPa to over 350 GPa) Time durations (~5 ns to μs) Focus on time-resolved, in-situ diffraction, scattering, and imaging measurements; simultaneous continuum measurements Special purpose experiments to complement dynamic compression Advanced Photon Source DCS Location A new paradigm to understand dynamic compression of materials at multiple length scales For more information on DCS contact Dr. Yogendra Gupta, WSU ymgupta@wsu.edu 3
Instrumentation Room DCS Layout Peak stresses: ~1 GPa to over 350 GPa Shock wave time durations: ~5 ns to microsecond Focus on diffraction and imaging measurements; simultaneous continuum measurements Control Room Beam Direction Impact Facilities Laser Shock Facility Special Purpose Experiments Front End Optics Energy range from 7-35 kev with energies to 100 kev for imaging Focused X-ray beam spot sizes: ~14 (V) x 20 (H) μm 2 to ~19 (V) x 68 (H) μm 2 Special purpose experiments to complement dynamic compression DCS measurements will address long-standing scientific questions regarding materials dynamics 4
Design philosophy emphasizes proven technology and operational robustness Laser is designed to be part of a high productivity user facility Laser uses technologies that are currently operating in the OMEGA, OMEGA-EP, and Multi-Terawatt (MTW) laser facilities at LLE. Controls software are being developed for ease of use and high reliability. Laser is designed to be flexible and upgradable to arbitrary pulse shape (with software upgrades) and higher repetition rate (with power amplifier development and upgrade) 5
DCS Laser Design Summary Parameter Laser energy Wavelength Repetition rate Spot size Value 100 J (3ω) 200 J (1ω) 351 nm (3ω) 1 shot every 20 minutes 500 µm flat top Prepulse contrast >10 6 :1 for 100 ns >10 8 :1 for 100 ms Shot to shot reproducibility <+/- 3.0% Pulse shape control <1 nsec rise to a 5 nsec pulse that starts at 70% of the peak intensity and linearly increases to 100% peak intensity over the 5 nsec. (Pulse 1) Operating Crew <1 nsec rise to a 10 nsec pulse that starts at 70% of the peak intensity and linearly increases to 100% peak intensity over the 10 nsec. (Pulse 2) 5 nsec linear ramp to 85% of peak intensity and linear increase to 100% peak intensity over an additional 5 nsec. (Pulse 3) 13 nsec linear ramp from 0% to 100% peak intensity followed by 3 nsec flat top at 100% peak intensity. (Pulse 4) Single trained operator 6
4 standard pulses will be preprogramed into the DCS laser. 120.00% Pulse Shape #1 120.00% Pulse Shape #2 100.00% 80.00% Rise time <1ns Fall time <1ns 100.00% 80.00% Rise time <1ns Fall time <1ns 60.00% 60.00% 40.00% 40.00% 20.00% 20.00% 0.00% 120.00% 100.00% -2-1 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 t (ns) Pulse Shape #3 0.00% 120.00% 100.00% -2-1 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 t (ns) Pulse Shape #4 80.00% 60.00% 40.00% 20.00% 0.00% Fall time <1ns -2-1 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 t (ns) 80.00% 60.00% 40.00% 20.00% 0.00% -2-1 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 t (ns) The DCS laser pulse shaping system is capable of arbitrary pulse generation. Fall time <1ns 7
Laser Schematic 200 J will be required in the IR for 100 J of UV (est. ~52% beam delivery losses) Injection laser system Fiber DFB Pulse shaping + SSD FM Nd:glass regen ~5 Hz ~20 mj FI Beam shaping Initial relay plane (RP0) FCC 4-pass rod amp ~2 J Optical Isolation Bypass mode for UV target alignment Multi-pass disk amplifier (using near-field angular multiplexing) ~ 3 min charge time Image relaying required after beam shaping (not shown) 150-mm disk amp G RP0 θ SSD ~200 J >100 J FCC DPP + DPR Focus lens ETP Target spot Final Optics + ETP Measurement All subsystems have been demonstrated in laboratory environments 8
Overall laser design layout 15 cm disk amplifier 1 rod amplifier Final optics (FCC, gratings, etc) Overall size 26 x 5 Regenerative amplifier 9
Regen is designed for a 20 ns pulse. Buildup photodiode Fiber input & Isolation Rod Camera 10.0 1 Amp not shown Switch in\out output Polarizer & rotator 4.5 Isolation Pockels Cell Diagnostic Pick-off & front end ASP Length can be reduced for OTS laser Switch in\out cavity polarizer 10
Diode pumped regen operates at <1% energy variability Amplifier fluorescence 100 bck_2_80_amps_tif 80 60 40 Horizontal lineout 20 0 250 500 750 1000 1250 col bck_2_80_amps_tif 100 80 60 40 Vertical lineout 20 0 200 400 600 800 1000 Energy (J) 0.006 0.005 0.004 0.003 0.002 0.42% Std. Dev. row mm 0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 Near field output 0.001 4.0 4.5 0 0 1000 2000 3000 4000 Time (s) 0.00 1.25 2.50 3.75 5.00 6.25 Regen is designed for 20 mj output. Lenses are on order to reach full energy. mm 11
Pre-amplifier will use a 1 Continuum laser head and a NIF like 4-pass architecture Apodizer Input/Output Polarizer 1 Continuum Amp 1:1 relay image telescope 1 Faraday rotator Regen not shown Beam expanding telescope Diagnostic pick-off & ASP Image plane after 2 nd pass Current design produced 1.6 J 12
Disk amplifier uses a multi-pass bow-tie design Input object plane 2.36 cm diameter Relay telescope for passes 5 & 6 Relay telescope for passes 1 &2 Relay telescope for passes 3 &4 Passes 1 & 2 Gain slabs Relay image plane 3.55 diameter 2 x 2 x 2 passes Magnification of 1.5 between every two passes 4 element relay imaging telescope (reduces required telescope length for imaging distance) Beam Sizes 2.36 cm (input) - 3.55 cm (pass 1,2) 5.33 cm (pass 3,4) 8 cm (pass 5,6) Relay imaging repeats after every 2 passes 13
Predicted main amp energy buildup 200-J IR output energy goal for DCS Peak single-pass small-signal gain = 2.73 100 J IR needed for OTS Passes 1 through 3 Transit optics (bend mirrors & telescopes) 14
Room layout at DCS facility 15
Web based GUI integrates all operations at a single location. Main GUI panel All diagnostics are collected and displayed on a single platform 16
Higher average power is possible with redesigned power amplifier DCS Front end and regen can run at 5-10 Hz Diode pumped pre-amplifier can produce sufficient seed energy at several hertz for the power amplifier Diode pumped thin disk amplifier has the potential to produce 100 J at 10 Hz 17
The DCS laser can be adapted for use with OTS Seed energy to disk amplifier can be reduced to bring energy to ~100J Number of passes could be reduced to 4, eliminating one telescope from the main amplifier A DCS type laser can be built in 18-24 months, depending on requirements. LLE equipment is designed into the laser for robustness and design maturity. A smaller laser could be developed, but it would require a redesign of the power amplifier. LLE is investigating alternative architectures to reduce overall footprint. 18