Developments in new high power fiber lasers and ultrafast lasers

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1 Institute of Applied Science, Friedrich Schiller University, Jena Developments in new high power fiber lasers and ultrafast lasers Martin Richardson Townes Laser Institute & College of Optics and Photonics, University of Central Florida, June 1, 2011

2 Townes Laser Institute at UCF Dedicated May ~ 57,000 students 2 nd largest university in USA New Florida Center of Excellence at the University of Central Florida COLLEGE of OPTICS & PHOTONICS Current Faculty 45 Graduate students ~ 180 Space ~ 105,000 sq ft Budget ~ $12M/yr High power fiber lasers Lasers in Medicine, Advanced Manufacturing & Defense. Economic Development Collaboration Agreement with Fraunhofer Institute for Laser Technology Aachen Industrial Laser Materials Processing

3 New professors in Optical Fibers Axel Schulzgen Professor (ex Univ. Arizona, Humbolt Univ.) Multi-structured optical fibers Phosphate fibers, Fiber lasers, NLO fibers Ayman Abouraddy Assistant Professor (ex MIT, Boston Univ) Multifunctional fibers, CG, polymer and photon band-gap fibers Biomed fibers Rodrigo Amezcua-Correa Research Assisant Professor (ex Southampton & Bath Universities) PCF fibers. Silica fibers

4 Outline Advances in High Tm fiber lasers Spectral control and tuning Pulsed laser operation in ns, ps and fs regimes Towards multi-kw power levels with spectral beam combining GMRF-line controlled lasers Dense spectral packing within Tm linewidth ( nm) Atmospheric transmission tests over 1 km Spectral tuning through water absorption lines First LIBS detection of organic signatures with Tm fiber lasers Advantages of Detection Next generation of high power ultrafast lasers CEP and quasi single cycle

5 Thulium Fiber Lasers Control of the spectral regime narrow linewidth output tunable emission stable frequency control Pulsed operation at 2 um Q-switched ns regime ps pulses with fs pulse mode-locking kw powers through beam combining initial demonstration dense wavelength stacking Available Power Including Atmosphere nm Wavelength Atmospheric Induced Cutoff 200 nm 100 pm Thulium Gain Cutoff V-parameter ~ λ -1 SRS thresh ~ λ -1 P crit (self-focusing) ~ λ -2 Applications of cw and pulsed Tm fiber lasers High power beam propagation Spectral sensing technologies Medical applications High Harmonic Generation

6 Thulium laser characteristics 6 Many Potential Pump Bands Different applications call for different bands 3 H ev 1.56 ev 790 nm pumping highly efficient High diode powers available Cross Relaxation process Quantum defect 40% CR allows >75% efficiency Multi-polar interaction between adjacent thulium ions allows energy transfer between them 3 H 5 3 F 4 3 H ev 1.03 ev 0.78 ev 0.69 ev 0.79 μm 0.09 ev 0 ev μm μm μm μm Single pump photon can generate two laser photons Potential Pump Bands Laser Cross Relaxation Energy Transfer Upconversion Multiphonon Emission Optimum doping High Tm doping levels needed Use of Al to minimize clustering in silica host which causes energy transfer up-conversion

7 Atmospheric transmission Propagation near 2 μm offers inherent benefits of increased MPE and reduced aerosol absorption. Blue: Atmospheric transmission between 0.8 and 2.2 μm Green: aerosol absorption (α = 0.18 km 1 at λ = 1 μm) Black: Relative laser Gain in Yb, Er Yb and Tm short length silica fiber lasers Red: Maximum Permitted Energy for 100 ns pulse (log scale). J-P. Cariou, B. Augere, M. Valla, C. R. Physique 7 (2006)

8 Volume Bragg Gratings (VBG) Glebov CREOL high efficiency >95% tunable (100 pm) Spectral control of the large Tm bandwidth Guided-Mode Resonant Filter (GMRF) Eric Johnson UNCC fixed wavelength by design linewidth (50 pm) Fiber Bragg Grating (FBG) Nufern Inc all-fiber, monolithic fabrication linewidth ~2.5nm

9 Monolithic FBG based Fiber Laser B. Sampson Nufern 200W 793nm PS-GDF-20/400 fiber 2.05µm Si filter Slope efficiency ~55% ~110W output power at 2050nm (FWHM ~2.5nm) from a grating based laser cavity E-O efficiency = 17% at 110W with 793 nm bars V eff = 2.05µm for 25/400 fiber 70W output at 1908nm Equation: y² = A + Bx + Cx² x y Amplitude (AU) A B C E E-05 R² x y Laser spectrum (AU) Ho:YAG absorption Atmospheric transmittance Laser Atmospheric Ho:YAG Wavelength (nm) Displacement (mm) Wavelength (nm)

10 300 W Stable, Tunable MOPA 2+1:1 PM Cladding Mode PM 10/130 Pump Stripper QWP QWP UDF 0.16NA Combiner t~5 m FC Grating L1 PM 10/130 TDF L3 Optical Isolator M3 HWP AC LD1 PM 10/130 UDF 0.16NA HWP L4 25/400 UDF 0.08 NA FC ~6 m 25/400 TDF AC L5 L2 LD1 M3 M1 25/400 UDF 0.08NA M2 L2 LD2 LD2 T. S. McComb et al.,appl. Opt, 49, 32, , ( 2010)

11 Power Amplifier Performance 8 W seed power Up to 220 W power Example slope at μm (65%) >1 hr Stability Tuning from μm μm FWHM <200 pm (MO limited) M 2 <1.2 Power (W) Slope ~65% y = x Launched Power (W) Power (W) > 170 nm Slope (%) Wavelength (nm) Wavelength (nm)

12 Volume Bragg Grating High Power Oscillator 1.0 VBG Reflectivity Grating tilted 0.6 in two axes Normalized Reflectivity (a.u.) Wavelength (nm) VBG or HR L1 25/400 UDF 0.09 NA AC ~5 m 25/400 TDF FC L3 L2 5 mm VBG Front Surface Uncoated 5 mm VBG Schematic 6 mm M1 25/400 UDF 0.09NA M2 L2 LD1 LD1

13 VBG Stabilized High Power Oscillator Output Power (W) HR Slope ~60% VBG Slope ~54% Spectral Power (a.u.) VBG Spectral Power HR Spectral Power HR Power VBG Power Launched Pump Power (W) Wavelength (nm) 159 W VBG Stabilized Power at 2053 nm 54% Slope (~5% less than for HR due to no AR coating on VBG) Stable spectrum < 1nm 10dB width (linewidth limited by VBG) M 2 <1.2 in all cases, independent of feedback >1 hr stable operation time. Power limited by onset of parasitic lasing

14 Tuning of VBG Laser Wavelength (nm) VBG Angle (degrees) VBG M2 60 L1 M1 L2 25/400 UDF 0.09 NA AC ~5 m 25/400 TDF LD1 FC 25/400 UDF 0.09NA L3 M2 L2 LD1 0.6 Rotation of VBG changes wavelength 50 W VBG Tunable Power 47-54% Slope >100 nm tuning range ( nm) Range limited by onset of parasitic lasing due to VBG design and fiber length Maximum Power (W) Maximum Power Wavelength (nm) Slope Efficiency Slope Efficiency (%)

15 Fiber Lasers based on Guided Mode Resonance Filters GMRF provided by collaboration with Eric Johnson (UNCC) OSA Signal (A.U.) 6.0x x x x x10-7 GMRF Spectral Reflectivity Transmission ~ 50 pm linewidth 1.0x10-7 Pump diode: 790nm 400 μm, 0.22 NA fiber, 30 W; 11 cm coiling diameter on heatsink Wavlength (nm)

16 Fiber Lasers based on Guided Mode Resonance Filters -20 GMRF HR Mirror Wavelength (nm) GMRF provided by collaboration with Eric Johnson (UNCC) > 10 W with GMRF linewidth < 100 nm R.A Sims, Opt. Lett, 36, 5, (2011)

17 Dense wavelength packing of Tm fiber lasers Dielectric Edge Mirrors (DEMs) Stacked Oscillators Beam Combiner Power Including Atmosphere Wavelength (nm) Principle Elements Dense stacking of narrow line (~100 pm) wavelength-specific lasers under effective bandwidth of 200 nm Beam Combiner utilizes high damage resistant Dielectric Edge Mirrors (DEMs) R.A Sims, et al., Opt. Comm, 284, 7, (2011)

18 Q-switched 2 um Tm fiber laser LIBS sensing Tm fiber laser: Wavelength:1992 nm Duration: 200 ns Energy: 100 uj Repetition rate:20 khz Focusing optics: 0.3 NA asphere Diameter: 10um Irradiance: 600 MW/cm 2 Spectrometer: Acton HRE Echelle Range: nm Resolution: 0.04 nm Acquisition: Delay: 0ns Duration: 300 ns Matthieu Baudelet et al., Optics Express (2010)

19 All-Fiber Picosecond Pulse Amplifier System 5 ps CNT Modelocked Laser 2050 nm Isolator 9/125 to 23/250 MFA Cladding Mode Stripper / Pump Dump ~2m 23/250 TDF 2+1:1 Pump Combiner 40 W 790 nm Pump Co-pumped LMA (23/250 TDF) all-fiber amplifier ~0.5 W Average power; Amplified at full 46 MHz ~11 nj pulse energy; Limited by feedback to modelocked laser due to poor isolation Improvements in Process Use Isolator for correct wavelength Higher seed power/preamp for better saturation and energy extraction More seed power -> higher efficiency Pulse down counter -> more per pulse energy Goals Reach microjoules level in conventional fiber Reach 10 s W average power Compare nonlinear thresholds to similar Yb lasers

20 Towards an all-fiber fs Tm laser Signal (db) Wavelength (nm) Signal (db) Wavelength (nm) Stretched Pulse Signal (db) Signal (db) Wavelength (nm) Amplifier Signal (db) Output Power (W) % Slope Efficiency Launched Pump Power(W) Output Energy (nj) Average Power 12.8 W 182 nj uncompressed pulses 60 nm Bandwidth Sims et al ASSP 2011

21 Innovative Science & Technology Experimentation Facility (ISTEF) A fully equipped laser ranging facility on Cape Canaveral Air Force Station Full laser and telemetry support 1 km (fully secure) range 5 km and 10 km ranges Many different receivers Beam image at ~300 m on 1 km range

22 1 km Atmospheric Propagation 2+1:1 PM Cladding Mode Grating L1 PM 10/130 TDF PM 10/130 Pump Stripper QWP UDF 0.16NA Combiner t~5 m FC QWP L3 Optical Isolator M3 GLP HWP AC LD1 PM 10/130 UDF 0.16NA HWP L4 25/400 UDF 0.08 NA AC ~5 m 25/400 TDF AC L5 L2 LD1 M3 M1 25/400 UDF 0.08NA M2 L2 LD2 LD2 Beam diameter measurements along the 1 km range confirm nearly diffraction-limited beam divergence The centroid moved between % of the full beam diameter corresponding to pointing variation of <45 μrad including beam distortion from atmospheric turbulence A 50 mm lens is used to collimated the beam from the fiber facet along a 1 km laser range

23 Initial 2 m Tm fiber laser propagation tests

24 High power lasers in the Richardson Labs TW Laser MFL MTFL HERACLES PhaSTHEUS fs 850 nm CPA Cr:LiSAF 300 mj 0.1 Hz 1 J single shot 40 fs 800 nm CPA Ti:Sapphire 40 mj 10 Hz 2mJ 1 khz 40 fs 800 nm CPA Ti:Sapphire 400 mj 10 Hz 5 fs 800 nm OPCPA CEP Hybrid 2 mj 10 khz 5 fs 800 nm OPCPA CEP Hybrid 100 mj 1 Hz High intensity laser plasmas Hard X-ray generation & imagi Air filamentation studies LIBS sensing studies Femtosecond spectroscopy Air filamentation studies Air filamentation studies LIBS sensing studies Standoff spectroscopy Attoscience EUV generation & applications THz studies Attoscience EUV generation & applications Stand-off THz studies Air filamentation studies

25 Energy scaling of few cycle systems 100 mj 10 mj 1 mj 100 J PhaSTHEUS Herrmann et al ASSP 2009 Krausz et al. CLEO, 2007 Adachi et al., Opt. Expr 2008 Witte et al., Opt. Expr 2006 HERACLES Mid IR systems 800 nm systems 10 J 1 J Tünnermann et al., Opt. Expr 2009 Chalus et al., Opt. Expr Hz 10 Hz 100 Hz 1 khz 10 khz 100 khz 1 MHz + HERACLES: High Energy Repetition rate Adjustable Carrier Locked to Envelope System

26 Architecture of HERACLES

27 Stretcher/Compressor strategy Technique implemented on HERACLES limits losses in compressor..low loss compressor enables higher output energy at low cost

28 mj, multi-khz, TEM 00 pump beam generation

29 Optical Parametric Amplifier Gain region Amplified spectrum supporting a 7.3 fs transform limited pulse

30 The high energy beam line

31 Summary New laser technologies are breathing new concepts into ultra-fast laser technologies Many new applications opening for ultra-short pulse lasers In addition to pressing to higher powers, we are pushing to towards shorter pulses, higher efficiencies, more compact and rugged systems. After 50 years of lasers After 25 years of ultrafast This field offers so much for the next generation of scientists and engineers

32 Educational Programs in Laser Marterials Processing NSF International REU Program in Optics, Lasers Photonics and Optical Materials International summer internship program for undergraduates 1998 present > 70 students 2 year program NSF Materials World Network Program In novel IR fibers ATLANTIS-MILMI Co-tutelle doctoral degree Program in Laser Materials Processing and Optical Materials Clemson University, UCF,Bordeaux University Turin University, Adelaide University University Central Florida Bordeaux University Clemson University, Friedrich-Schiller Univ. University Central Florida Clemson University Bordeaux U Mobility program ~ 20 students 2008 present International MS degree Lasers and Materials Interaction Science ~ 16 students 2004 present Joint Ph.D 7 graduates expansion

33 Acknowledgements Funding JTO-HEL Office ARO NAVAIR Industrial Affiliates

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