University of Texas Tri-Color Terawatt (UT3) Laser System

This new state-of-the-art facility consists of 3 subsystems:

 

1.) 45 TW, 25 fs ultrahigh contrast Ti:S laser system (THALES Laser)
This is the newly purchased component of the UT3 system.  This acquisition developed along the following timetable:

May 2006:  University of Texas committed $ 1 M capital equipment funds
Summer & Fall 2006:  consideration of several potential vendors
December 2006:  University of Texas issues formal bid invitations
January 2007:  Contract awarded to THALES Laser
February 2007:  Design review and approval meeting at manufacturer’s site
December 2007:  Test of system at THALES factory site in Paris, France.
February 2008:  Delivery, installation & final test of ALPHA 10/XS 45 TW system

The main components of the ALPHA 10/XS 45 TW system are:

  1. FEMTOPOWER Compact Pro front end, including Model Synergy 20 oscillator from Femtolasers GmbH, with chiller.  Oscillator includes FEMTOLOCK option to synchronize to external RF clock to drive customer’s Nd:YAG channeling/machining laser system.
  2. Cross-Polarized Wave (XPW) Filter to enhance pulse duration and contrast
  3. Acousto-optic programmable filter (Model Dazzler 800 WB) to enhance pulse shaping
  4. ALPHA 10/XS 45 TW amplifier system within 2 breadboards (excluding compressor):
    • Öffner triplet stretcher
    • 10 Hz multi-pass amplifier including PREAMP and AMP-1 with Ti:S crystals water-cooled using THALES Laser patent No. 04 11815.
    • ~ 30 mJ uncompressed output split off to drive customer’s Raman shifter/amplifier subsystem
  5. Pump laser (Model JADE) for kHz preamplifier, with remote computer control.
  6. 3 Pump Lasers (Model SAGA HP) for 10 Hz amplifiers, with remote computer control.
  7. COMPRESSOR (in vacuum tank provided by customer).  THALES provides:
    • motorized 10-6 Torr vacuum-compatible mounts with remote control software & electrical feedthroughs
    • all optics including gratings mounted on aluminum plate.
  8. MASTER CLOCK to synchronize all signals and secure laser operation.  This delay generator is provided with computer and user-friendly software in Labview to allow user to develop additional control routines. Extra trigger outputs at T0 – 1 ms and T0 – 1 µs with precision better than 1 ns are included. 

The major specifications of the ALPHA 10/XS 45 TW system are:

Peak power: >45 TW                       Energy stability: 1.5 % (rms)
Wavelength: 800 ±15 nm                Contrast ratio: >1010: 1 @ > 20 ps;  > 108 @ 10 ps;    >107:1 @ 5ps
Pulse duration: < 25 fs                                             >106: 1 @ 1 ps  (> 107:1 ns prepulse contrast)
Output energy: 1.13 J                     Spectral width: > 50nm
Repetition rate: 10 Hz                     Strehl ratio: > 0.7                               
Pointing Stability: < 20 µrad           Synchronization:   < 30 ps

Thales Laser System
Dr. Erhard Gaul and Prof. Mike Downer scrutinize the new ALPHA XS/10 45 TW system at the THALES Laser factory in Paris in December 2007.  The entire system fits on a 5’ x 15’ optical table.  The FEMTOPOWER compact PRO in the foreground is the front end, producing micro-Joule level, 25 fs pulses.  The aluminum cylinder is a vacuum chamber housing the cross-polarized wave (XPW) system that improves peak-to-pedestal pulse contrast to > 1010:1 at > 20 ps from the peak, and broadens pulse bandwidth to >50 nm as shown on the laptop screen.  Heat-generating power supplies are sequestered in a mechanical room outside the clean room. 


 
 
  

2)  Nd:YAG “machining” laser system


This system will be synchronized to the ALPHA 10/XS 45 TW system with <30 ps jitter.  Built by former graduate student E. Gaul in 1996-7, the system has been used to generate plasma channels [Gaul00, Zgadzaj04] in past research. In proposed research, it will also be used as a machining laser to truncate non-uniform regions of a gas jet, leaving a uniform “top-hat” profile [Pai05].  It consists of the following components:  (1) A Coherent Antares 76-S mode-locked Nd:YAG laser (1 µm, 100 ps, 76 MHz, 20 W average power); (2) a home-built self-filtering regenerative pre-amplifier with a flashlamp-pumped Nd:YAG rod, including an intra-cavity etalon to broaden the pulses to 400 ps (1 mJ, 10 Hz); (3) a homebuilt 2-pass flash-lamp-pumped Nd:YAG pre-amplifier; (4) a Kigre single-pass Nd: YAG power amplifier that produces 1 J, 400 ps pulses. Synchronization with the Ti:S system is achieved by mixing a 76 MHz master clock signal from the Antares mode-locker with a 76 MHz photodiode signal from the Ti:S oscillator output. A difference-frequency signal is then fed back to a piezoelectric transducer that dithers the Ti:S cavity length until it exactly matches the Antares cavity length.

 

3) Chirped-Pulse Raman Amplifier (CPRA)


For his Ph.D. project, graduate student Franklin Grigsby developed a subsystem that generates millijoule-level Stokes (873, 961 nm) and anti-Stokes (738, 685, 639 nm) sidebands of 800 nm terawatt pulses by inserting a multi-stage barium nitrate Raman shifter-amplifier into a conventional Ti:sapphire chirped pulse amplification system [Grigsby08].  The Raman subsystem requires no additional pump lasers and does not compromise the energy, duration or beam quality of the main 800 nm pulses.   The chirped first Stokes (870 nm) beam is compressed to transform limit (~100 fs) with several mJ energy, and has high beam quality, free of filamentation.  Synchronized 800 nm and Raman sideband pulses are useful for a variety of two-color high-intensity laser experiments.  For example, the secondary pulse can serve as a spectrally distinct, low group-velocity-walkoff probe in cm-scale plasma waveguides [Zgadzaj04], or to induce beat-frequency modulation on the main pulse in order to seed the growth of a plasma wakefield via the forward Raman instability [Fomytskyi05].  It can also be used to realize two-color laser-plasma interaction schemes that underlie theoretical proposals to amplify [Shvets98], compress [Kalmykov05], and focus [Gibbon90] intense laser pulses in plasmas.  Graduate student J. C. Sanders will pursue some of these experiments. 

  • [Grigsby08]     F. Grigsby, D. Peng, M. C. Downer, “Chirped-pulse Raman amplifier for high-intensity two-color experiments,” J. Opt. Soc. Am. B 25(3), in press (March 2008). 
  • [Shvets98]        G. Shvets, N. J. Fisch, A. Pukhov and J. Meyer-ter-Vehn, ``Superradiant amplification of an ultrashort laser pulse in a plasma by a counterpropagating pump," Phys. Rev. Lett. 81, 4879-4882 (1998).
  • [Kalmykov05]   S. Kalmykov and G. Shvets, ``Compression of laser radiation in plasmas via electromagnetic cascading," Phys. Rev. Lett. 94, 235001 (2005).
  • [Gibbon90]        P. Gibbon, ``The self-trapping of light waves by beat-wave excitation," Phys. Fluids B 2, 2196-2208 (1990).

raman
Schematic of Raman shifter and two-pass Raman amplifier.  Top:  photograph of Raman cascade output of first pass of Raman amplifier, with intersection angle of pump and seed adjusted to optimize phase matching.  Relative intensities in the photograph are determined by fluoresce efficiency of the screen (dashed line) and detection efficiency of the camera, and do not indicate relative intensities emerging from the crystal.  The screen is removed in normal operation.