1. Optics, Lasers, and Remote Sensing Department 1128 Microlasers and Nonlinear Optics R. Schmitt, D. Armstrong, A. Smith, B. Do, and Greg Hebner Sandia National Laboratories Laser, Remote Sensing, Plasma Physics and Complex Systems Department 1128 Sandia is a multiprogram laboratory operated by Sandia Corporation, a Lockheed Martin Company, for the United States Department of Energy’s National Nuclear Security Administration under contract DE-AC04-94AL85000.

2. Optics, Lasers, and Remote Sensing Department 1128 Emerging and enabling technologies require investment Long history of atomic and molecular physics –Spectroscopy, optical surface diagnostics Fiber lasers –Emerging compact high power sources. Frequency extension, nonlinear optics –Generate wavelength(s) matched to the mission requirements. –Recent advances in nonlinear optics understanding are enabling new system designs. Exploiting the THz region of the EM spectra –New source and detector technology is opening up the THz spectral region. –High chemical specificity, unique and not widely published spectral signatures, low probability of intercept, broad area imaging using SAR like processing. Compact, robust sources –Micro lasers, high power in a small size. –Solid-state and semiconductor laser systems UV solid state lasers are relatively well developed at 400 nm with 290 nm sources on the horizon. Wavelengths are a good fit to some remote sensing opportunities. 0.6 THz image

3. Optics, Lasers, and Remote Sensing Department 1128 Basic design for passively Q-switched microlaser fiber-coupled diode laser pump (electrical isolation) passively Q-switched (electrical isolation) Cr:Nd:GSGG active material (rad hard) Cr 4+ :YAG Q-switch (rad hard) simple cavity with mirror coatings directly on crystal faces crystals bonded together to form rugged, monolithic laser thermal lensing and gain guiding stabilize flat-flat cavity Cr:Nd:GSGGCr 4+ :YAG 1.06  m output pulse lens808-nm pump light Fiber

4. Optics, Lasers, and Remote Sensing Department 1128 The Cr:Nd:GSGG microlaser produces ~1.6-ns-wide pulses E out = 57 μJ / pulse ~1.6 ns (FWHM) pulse width raw beam I mean ~ 150 MW/cm 2 after-pulse is common –~15 - 25% total energy in second pulse typical –affected by details of pump focus, pump beam quality linearly polarized (>100:1) near field beam intensity (MW/cm 2 )  output energy is scalable from μJ to 100’s of μJ

5. Optics, Lasers, and Remote Sensing Department 1128 The Cr:Nd:GSGG microlaser produces excellent beam quality The near-field beam diameter (1/e 2 ) is 150 μm (h) x 144 μm (v). The far-field divergence (1/e 2 full angle) is 10.2 mRad (h) x 10.6 mRad (v). M 2 ≈ 1.05 (fitted second moment beam diameter to propagation equation) E out = 57 μJ / pulse  F peak = 0.67 J / cm 2  I max ~ 300 MW/cm 2 (raw beam) scan through focus

6. Optics, Lasers, and Remote Sensing Department 1128 laser 1 2 3 Waveguides written directly into bulk material can be used for optical interconnects Bulk optical waveguide elements provide functional “circuits” while fibers provides the “wires”. Waveguide structures are a building block for buried optical computing. All optical interconnects are a significant safety improvement. –Alignment and materials are very robust but if broken, can be time consuming to repair. Waveguides in bulk material fail based upon well understood material properties (heat, water). Phase contrast image of a waveguide written in borosilicate glass Ring coupling structures have been manufactured using femtosecond laser machining. Near field mode profile of a laser written waveguide is near Gaussian. Writing custom optical elements directly into bulk glass

7. Optics, Lasers, and Remote Sensing Department 1128 Tunable high pulse energy UV: A difficult problem Typical method: SFG using Nd:YAG-pumped ns OPO signal + Nd:YAG 2  –803 nm + 532 nm  320 nm Many problems to overcome: –High-energy ns OPO beam quality is poor –Nanosecond OPO’s start late and back-convert –Q-switched Nd:YAG beam quality is poor Signal Depleted pump F  200 Critical direction  OPO signal far-field fluence SPIE 5887-3

8. Optics, Lasers, and Remote Sensing Department 1128 Image rotating nonplanar ring “RISTRA” OPO “ RISTRA” cavity: Rotated Image Singly- Resonant Twisted RectAngle JOSA B 19, 1801–1814 (2002) /2 Pump in /2 Pump out OPO: xz-cut KTP,  = 58.4  803(e) + 1576(o)  532(o) 10 × 10 × 15 mm 3 SFG crystal Type-II BBO,  = 48.2  803(e) + 532(o)  320(e) Pulsed “self seed” beam UV out Signal out Mechanically robust. Long-term stability No mirror adjustments 1.975" SPIE 5887-3

9. Optics, Lasers, and Remote Sensing Department 1128 Near- and far-field = 803 nm signal fluence profiles Fresnel #  D 2 / L > 450 for Signal = 803 nm Far field: Lens with effective f/#  77 Near field: Image of OPO output coupler SPIE 5887-3

10. Optics, Lasers, and Remote Sensing Department 1128 Pump depletion for seeded and unseeded oscillation Self-seeded oscillation in two-crystal RISTRA ~85% pump depletion Free-running oscillation in two-crystal RISTRA ~37% pump depletion SPIE 5887-3

11. Optics, Lasers, and Remote Sensing Department 1128 Are flat-top beam profiles important? 2nd-order Gaussian pump 0th-order Gaussian seed ~52% pump depletion Flat-top pump 100 mJ flat-top seed 10 mJ Pump depletion = 93% Flat-top pump 100 mJ Gaussian seed 10 mJ Pump depletion = 92% Flat-top pump Flat-top seed ~ 85 % pump depletion SPIE 5887-3

12. Optics, Lasers, and Remote Sensing Department 1128 Maximum extra-cavity UV energy ~ 190 mJ Detector: Scientech 380101 absorber Calibration: 1 mJ/mV @ 10 Hz Transmission loss: ~5% Efficiency: 1064 nm to 320 nm > 21% Scientech 380101 Depleted SFG Pulses 67 % depletion of 803 50 % depletion of 532 UV energy ~ 180 mJ SPIE 5887-3

13. Optics, Lasers, and Remote Sensing Department 1128 End