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The progress in near and mid-IR ultrafast laser systems at Q-Peak

Evgueni Slobodtchikov Q-Peak, Inc.

DEPS Ultrafast Workshop 2009

Outline

· ·

Motivation Near IR portable ultrafast CPA laser system for LIBS 10 MHz ultrafast Yb:CaF2 laser system for micromachining Mid IR ultrafast laser system

­ Cr:ZnSe femtosecond oscillator

·

· ·

Conclusion

DEPS Ultrafast Workshop 2009

Motivation

Goal: development of practical femtosecond laser sources in near (~1 m-wavelength) and mid-infrared (IR) (2-5 m wavelength) spectral ranges with high pulse energy output (0.1-1 mJ). Recent advances: high power cw fiber-coupled diode lasers, high-power Tm:fiber lasers, development of new laser materials. List of outside-of-lab applications for fs lasers is growing rapidly. Some of them are: ·LIBS ·Industrial micromachining ·Medical Imaging ·Rapid prototyping

DEPS Ultrafast Workshop 2009

Yb-doped laser media for near-IR lasing

Material Yb:CALGO Yb:phosphate glass Yb:YVO4 Yb:BOYS Yb:SYS Yb:KYW Yb:GdCOB Yb:KGW Yb:CaF2

DEPS Ultrafast Workshop 2009

t (fs) 47 58 61 (KLM) 69 70 71 (KLM) 89 100 150

central (nm) 1050 1080 1050 1062 1070 1025 1045 1037 1047

emission (x10-20 cm2) 0.75 0.05 0.14 0.3 0.44 3 0.35 2.8 0.25

fluo (ms) 0.42 1.3 0.3 1.1 0.44 0.6 2.6 0.35 2.4

K (W/m/K) 6.3-6.9 0.85 5.2-5.11 1.8 1.6-2.8 3.3 2.1 3.3 9.4

Ytterbium doped crystals

A very simple structure

·No undesired effects

Weak quantum defect

·Low thermal load

Diode pumping around 980 nm

·"Broad" emission spectrum (100 fs pulses possible)

Yb3+

2F 5/2

2F 7/2

Crystal field

N2

980 nm 1.05 m

2F 5/2

N1

DEPS Ultrafast Workshop 2009

2F 7/2

Absorption and emission spectrum of Yb: CaF2

DEPS Ultrafast Workshop 2009

Near-IR diode-pumped Yb:doped CPA system

Diode-pumped PDR Yb:KGW oscillator 2.7 ps, 1.5 nJ, 1042 nm, 100 MHz

Pulse stretcher 2.7 ps 200 ps

Diode-pumped Yb:CaF2 regenerative amplifier 2 mJ, 250 Hz, 1047 nm

output 1050 nm, 600 fs, 1.7 mJ, 250 Hz

Pulse compressor

DEPS Ultrafast Workshop 2009

Yb:KGW femtosecond oscillator in PDR

Femtosecond Yb:KGW laser in Positive Dispersion Regime (PDR) generates 2.7 ps pulses (positively chirped). Negative GVD compresses it to 320 fs. PDR provides extremely robust mode-locked operation due to lower peak power and reduced nonlinear effects.

DEPS Ultrafast Workshop 2009

Yb:CaF2 regenerative amplifier

0.005 experiment gaussian fit 650 fs x 1.47 0.003 0.002

0.004

0.001

0 -2 -1.5 -1 -0.5 0 0.5 1 1.5 2

Stretching-compression is accomplished through the use of Chirped Volume Bragg Gratings (OptiGrate).

DEPS Ultrafast Workshop 2009

Pulse energy 1.7 mJ at repetition rate 250 Hz. ·Pulse duration 650 fs.

Diode-pumped Yb:doped ultrafast laser system

Laser output

Laser head

Air-cooled power supply

DEPS Ultrafast Workshop 2009

3D model of the packaged diode-pumped Yb:doped system

DEPS Ultrafast Workshop 2009

Diode-pumped Yb:doped ultrafast laser system (laser head)

DEPS Ultrafast Workshop 2009

10 MHz ultrafast Yb:CaF2 laser system for micromachining

M5 M6 output M1 M4 M7 FC diode pump 980 nm, 15 W P2 SBR P1

pump telescope M8

M3

M2

Yb:CaF2

M9

Parameters Average output power Repetition rate Pulse energy Pulse duration Peak power

DEPS Ultrafast Workshop 2009

IR output 1050 nm 1W 10 MHz 100 nJ 320 fs 312 kW

SHG 525 nm 0.5 W 10 MHz 50 nJ 270 fs 180 kW

Laser-assisted silver deposition with SHG (525 nm)

Experimental setup

DEPS Ultrafast Workshop 2009

Scanning electron microscope image (silver lines are 2 um wide)

Mid-IR ultrafast CPA high power laser system

DEPS Ultrafast Workshop 2009

Properties in comparison

Cr:ZnSe

Crystal structure Thermal conductivity Thermooptics dn/dT Third order nonlinearity n2 Two-photon absorption Second-order nonlinearity Peak emission cross-section em at 0 Fluorescence bandwidth Relative bandwidth /0 Peak pump cross-section abs at max Lifetime at room temp. Isat = h/em Direct diode pumping DEPS Ultrafast Workshop 2009 Cubic 18 W/m°C 70·10-6 1/ °C 180·10-20 m2/W at 1.6 µm*) band gap 2.83 eV very high: 30 pm/V 13 ·10-19 cm2 2450 nm 1000 nm (50 THz) 0.49 11 ·10-19 cm2 1780 nm 6 µs 11 kW/cm2 Yes

Cr:ZnS

Cubic-uniaxial 17 W/m°C 27 W/m°C (cubic) 46·10-6 1/ °C <180·10-20 m2/W 3.84 eV <30 pm/V 14 ·10-19 cm2 2350 nm 800 nm (43 THz) 0.34 10 ·10-19 cm2 1690 nm 4.3 µs 14 kW/cm2 Yes

Ti:Sapphire

Uniaxial 28 W/m°C 12·10-6 1/ °C 3·10-20 m2/W ~8 eV absent 4.5 ·10-19 cm2 780 nm 300 nm (130 THz) 0.57 0.65 ·10-19 cm2 500 nm 3 µs 210 kW/cm2 No

Pumping options for Cr:ZnSe laser

· Femtosecond oscillator can be pumped directly by Tm:fiber laser.

Er:fiber

Tm:YALO Tm:YAG

Tm:fiber Ho:YLF Cr:ZnS Cr:ZnSe

·

InGaAsP diodes

Similar to Ti:S due to short upper state life time (6 s) the amplifier has to be pumped by high energy source. Ho:YLF laser can be used as an energy storage:

­ can be pumped by Tm:fiber laser ­ 2.05 m output is ideally suited for high energy pumping of Cr:ZnSe with low thermal stress.

1200 1400

·

Co:MgF 2

GaSb diodes

1600

1800

2000

2200

2400

2600

Wavelength, nm

DEPS Ultrafast Workshop 2009

State-of-the-art in Cr:ZnSe lasers

Laser characteristics CW, output power, W CW, tuning range, nm CW, efficiency, % Pulsed, output power, W Output parameter Reference 12 2000-3100 70 18.5 @ 10 kHz Moskalev et al., 2008 Sorokina et al., 2004 Mond et al., 2001 Carrig et al., 2004 Koranda et al., 2006 Demirbas et al., 2006 Sorokina et al., 2007 Moskalev et al., 2008

Pulsed, output energy, mJ 14 @ 200 s Pulsed, tuning range, nm SBR mode-locked KLM mode-locked 1880-3100 80 fs @ 80 mW ~300 fs @ 50 mW

DEPS Ultrafast Workshop 2009

Mid-IR fiber laser-pumped Cr:ZnSe CPA system

2.05 m Ho:YLF Q-switched pump laser 17 mJ, 1 kHz

1.94 m Tm:fiber CW pump laser 5W 2.5 m

Femtosecond Cr:ZnSe laser 100 fs, 10 nJ, 100 MHz

60 W

Pulse stretcher 100 fs 100 ps

2.5 m Cr:ZnSe regenerative amplifier 8 mJ, 1 kHz

Output:

2.5 m 100-200 fs ~ 1 mJ 1 kHz

DEPS Ultrafast Workshop 2009

Pulse compressor

Femtosecond Cr:ZnSe oscillator

C aF 2 pris ms

T m:fiber las er

C r:Z nS e

2% O .C .

R O C = 100 mm

S E S AM

R O C = 150 mm

1.2 1.0 Reflectance 0.8 0.6 0.4 0.2 0.0 2.2 2.4 2.6 2.8 3.0

No coating etched to 94 nm

Cavity setup of mode-locked Cr:ZnSe laser. The reflectivity curve of SESAM (NRL).

Wavelength ( m )

DEPS Ultrafast Workshop 2009

Water vapor absorption between 2.5 and 2.6 µm

1 0.9 0.8 0.7 Amplitude [au] 0.6 0.5 0.4 0.3 0.2 0.1 0 2500 2510 2520 2530 2540 2550 2560 2570 2580 2590 2600 Wavelength [nm]

Plot of water absorption lines between 2.5 and 2.6 µm (red) and the output spectrum of Q-switched Cr:ZnSe laser (blue) without N2 purging.

DEPS Ultrafast Workshop 2009

Femtosecond Cr:ZnSe oscillator

DEPS Ultrafast Workshop 2009

Femtosecond Cr:ZnSe oscillator

1 0.9 0.8 0.7 M a gnitude [au ] 0.6 0.5 0.4 0.3

1 0.8 0.6 0.4 0.2 0 -0.2 -200 -100 0 Time [fs] 100 200

A m plitude [au]

0.2 0.1 0 2400 2425 2450 2475 2500 2525 2550 2575 2600 2625 2650 Wavelength [nm]

Autocorrelation trace (left) and spectrum (right) of mode-locked Cr:ZnSe laser with a FWHM pulse duration of 130 fs. The spectrum was centered at 2530 nm with a FWHM of 50 nm.

DEPS Ultrafast Workshop 2009

Femtosecond Cr:ZnSe oscillator in f-2f interferometer for CEP stabilization.

f2f interferometer

HR 1.6 µm dichroic mirror AgS e

1.6 µm BPF

Monochromator

HR 3.2 µm octave s pectrum

PD

f0

As S e fiber

T m:fiber las er C r:Z nS e Modelocked las er

Autocorrelator S HG P D

PD

2.5 µm error s ignal

L ocking electronics

DEPS Ultrafast Workshop 2009

Supercontinuum generation in AsSe fiber

Magnitude [linear] 1

Laser Fiber

0.5

0 2350

0

2400

2450 2500 Wavelength [nm]

2550

2600

Magnitude [log]

10

2300

2350

2400 2450 2500 Wavelength [nm]

2550

2600

DEPS Ultrafast Workshop 2009

Conclusions

·

We completed the development of first truly portable ultrafast near-IR high power CPA laser system based on Yb:doped crystal. We demonstrated the prototype of femtosecond Cr:ZnSe oscillator as a seed source for high power mid-IR laser system.

·

DEPS Ultrafast Workshop 2009

Acknowledgments

· The work is supported by SBIR Phase II and STTR Phase I programs from AFRL (DE) and ARL.

DEPS Ultrafast Workshop 2009

Information

Development of near and mid-IR

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