Advanced Solid State Lasers for Lidar Systems - Q … 1998.pdfJuly 9, 1998 Ilrc98.ppt KTP-family...

Advanced Solid State Lasersfor Lidar Systems

Peter F. Moulton19th International Laser Radar Conference

Annapolis, MarylandJuly 9, 1998

July 9, 1998 Ilrc98.ppt

What is Q-Peak???

Research Division of Schwartz Electro-Optics, Inc.

SEO Boston (name change)

Q-Peak, Inc. (wholly owned subsidiary)


Credits

• Researchers– Glen Rines, Richard Schwarz, Andy Finch, Mark Webb– David Welford, Jeff Russell, Kevin Wall, Anton Zavriyev,

Yelena Isyanova, Kevin Snell, Dicky Lee, Jeff Manni, Alex Dergachev, Bhabana Pati

• Collaboration– Ushio, Inc. (UV generation)

• Government Support– NASA Langley (OPOs, Ti:sapphire UV generation)– NASA Goddard (microlasers)– Army ERDEC (OPOs, Ti:sapphire UV generation)– DARPA (intracavity OPOs)– Air Force (Ti:sapphire, OPOs)


Outline

• Lamp-pumped, compact Nd lasers• High-energy OPOs for eyesafe systems• Ti:sapphire lasers for UV generation• Tandem OPO for mid-IR generation• CW, diode-pumped lasers for next-generation

lidar systems


Properties of Compact Laser Head (CLH)

• Rugged, compact, flashlamp-pumped 1-micron laser• Nd:YLF oscillator / amplifier design• Output: 700 mJ @ 10 - 30 Hz @ 1053 nm (15 ns pulse)• Beam quality: M = 15• Optical head: 5" x 6" x 17", 16 pounds• All optics hard-mounted; final alignment w/ Risley wedges• Power supply & closed-loop cooler in shock-mount cases• Serves as multipurpose pump source

– Pump for NCPM KTP-family OPOs– Frequency doubled for Ti:sapphire pumping


Input-Output curves for CLH are independent of pulse rate to 30 Hz

0 20 40 60 800

200

400

600

800

Lamp Energy (J)

1053

-nm

Out

put (

mJ)

10 Hz

20 Hz

30 Hz


CLH Photograph


Optical Parametric Oscillators (OPOs)

• Optical parametric oscillators are nonlinear optical devices that convert a fraction of the output of a laser (the pump) into two outputs, the signal and idler, both at longer wavelengths

• The frequencies of the signal and idler sum to that of the pump

• For a given pump, the signal and idler wavelengths are determined by the characteristics of the nonlinear crystal used in the OPO


KTP-family OPOs are used as eyesafe sources

• Several crystals belonging to the KTP family, when pumped by Nd-doped laser pumps around 1050-1070 nm, generate signal wavelengths around 1550 nm, the maximally eyesafe wavelength region

• The advantages of the KTP family include:– non-critical phase-matching, which allows good OPO

conversion efficiency even with poor-beam-quality pump lasers

– large available crystal sizes, which allows generation of high energies


0

100

200

300

400

500 15

71-n

m O

PO

Out

put

0.2 0.4 0.6 0.8 1 1.2 1064-nm Pump Energy (J)

4.5 W average power

KTP OPO generated a record energy in 10ns pulses


KTP OPO engineered for CLH


Picture of complete OPO-based lidar


KTA OPOs generated record powers at 100 Hz

0 20 40 60 80 100 1200

5

10

15

20

25

30

35

Pump Power (Watts)

Sign

al P

ower

(Wat

ts)


Biological Standoff Detection System (BSDS)


Laser-pumped, high-energy Ti:sapphire laser

Pump #1

Pump #2

Output

GRM

Ti:sapphirecrystals

Prisms

HR

Developed with NASA Langley, DARPA support, 1986-1992


Ti:sapphire input-output, 727-960 nm

0

50

100

150

200

250

300

350

400

450

500

0 200 400 600 800 1000 1200 1400

Green pump energy (mJ)

Ti:s

apph

ire

outp

ut e

nerg

y (m

J)

790 nm727 nm911 nm960 nm


Harmonic generation extends Ti:sapphire wavelength coverage for DIAL

700 750 800 850 900 950Wavelength (nm)

NO2

Benzene

Hg

Toluene Ozone

NO

SO2

Cl2

2nd

3rd

4th

Harmonic


Ti:sapphire provides high energies at fundamental and harmonics

• Fundamental (700 - 980 nm region)– > 400 mJ at selected wavelengths

• Second Harmonic (350 - 490 nm region):– 250 mJ at selected wavelengths (60% conversion)

• Third Harmonic (233 - 327 nm region):– > 40 mJ at selected wavelengths (254, 290 nm)– Currently investigating double-pulse system for ozone lidar,

improved harmonic conversion• Fourth Harmonic (210 - 245 nm region):

– 10 mJ at selected wavelengths


Tandem OPO provides broad IR wavelength coverage

Nd-doped,Q-switched laser KTA OPO CdSe OPO

IR seed source

IR seed source

Nd-dopedseed laser

1.5 - 3.6 μm

3.3 - 11 μm


Tuning curves for Tandem OPO design

1.52

2.53

3.54

4.55

5.56

6.57

7.58

8.59

9.510

10.511

45 50 55 60 65 70 75 80 85 90 95

Angle (degrees)

CdSe idlerCdSe signalKTA idlerKTA signal

Hydrocarbons

Wavelength (um)

Mustard gas

CO, HF

HCl

Strong water absorption


Input-output curves for KTA OPO

0

20

40

60

80

100

0 50 100 150 200Pump pulse energy, mJ

OPO

pul

se e

nerg

y, m

J

Total, 80%R OCIdler, 80% R OCIdler, 96% R OC Pump: 1053 nm

Signal: 1514 nmIdler: 3456 nm(x-cut crystal)

Also:Signal: 1483 nmIdler: 3631 nm(y-cut crystal)


Next-generation lidar sources will be cw pumped

• The current generation of solid state lidar sources is based on lamp-pumped Nd-laser technology

• Diode-pumped solid state lasers are more reliable, more efficient and provide better beam quality per W of output power

• Diodes are cw devices - they produce essentially the same power whether pulsed or cw

• Generation of high pulse energies requires many diodes -and many $$

• The most output per $ occurs for cw diode-pumped solid state lasers


CW-pumped lidar sources

• CW-pumped repetitively Q-switched lasers are common in industry for applications such as materials processing, marking and IC trimming

• Diode-pumped, repetitively Q-switched lasers can produce 10-20-ns pulsewidths (or shorter) under the right conditions, and thus providing range resolution comparable to pulsed-pumped lasers

• For the same average power, the trade-off is that the repetitively Q-switched sources will produce high pulse rates and lower pulse energies

• More sophisticated signal averaging is needed• Nonlinear devices can work well at the high rates, providing

frequency diversity


Nd:YLF “Gain Module” uses transverse pumping

20-W linear array

20-W linear array

Cylinder lens

Cylinder lens

Nd:YLF crystal

Cavitymode

Multi-pass design extracts large fraction of available power in TEM00 mode, has high gainLow average excitation density minimizes stress, beam distortionSimple, single-element pump optics


0

1

2

3

4

5

6

7

1 10 100

PULSE RATE (kHz)

PULS

E EN

ERG

Y (m

J)

7

8

9

10

11

12

13

14

AVE

RA

GE

POW

ER (W

)

PULSE ENERGY DATATHEORY (450 us)AVERAGE POWER DATA

Note!

Q-Switching results for single gain module show >12 W above 10-kHz PRR


MOPA #1 design generates higher power

AOQ-switch

Gain module

Diode Laser bar

Nd:YLF Oscillator

FaradayIsolator

1st StageAmplifier

2nd StageAmplifier

29W @ 5kHz37W CW

19W @ 5kHz25W CW

11.5W @ 5kHz13.5W CW

Nd:YLF slab

M = 1.07 (H), 1.1 (V)2


MOPA #2 design uses a two-gain-module oscillator, generates 0.6-MW pulses at 5 kHz

EOQ-switch

Two-module Nd:YLF Oscillator1st StageAmplifier

2nd StageAmplifier

50 W CW40 W Q-Sw @ 5 kHz

14-ns pulsewidth

Cylinderlens

Cylinderlens


Two-gain-module oscillator generates 14-ns pulses at a 5-kHz pulse rate

10 ns per division


Harmonic conversion generates visible, UV power

5HGCLBO

4HGCLBOBBOSHG LBO

Oven

0

1

2

3

4

5

6

7

0 2 4 6 8 10 12 14 16

SHG Average power (W)

4HG

Ave

rage

pow

er (W

)

0

10

20

30

40

50

60

70

Con

vers

ion

effic

ienc

y(%

)FHG powerEfficiency

Best results:

SHG (523.5 nm):14 W at 5 kHzand 65% conversionin LBO

4HG (262 nm): 6.6 W (internal)at 5 kHz with CLBO2.5 W at 10 kHz in BBO

5HG (207 nm):2 W (internal)at 5 kHz with CLBO


Ti:sapphire laser pumped by doubled Nd:YLF laser has 44% conversion efficiency at 10 kHz PRR

0

20

40

60

80

100

120

140

0 0.2 0.4 0.6

Ein (mJ)

T P (n

s)

0

0.05

0.1

0.15

0.2

0.25

E out

(mJ)

52% slope


OPOs provide high power at eyesafe wavelengths

AOQ-switch

Gain module

Diode Laser bar

Nd:YLF slab KTA 25 mm

Intracavity OPO1 W output

at 1507 nm

12.5 kHz PRR

6 ns pulsewidth

0

1

2

3

4

5

6

0 2 4 6 8 10 12 14

Pump power (W)

Sign

al p

ower

(W)

External OPO

Q-SW Pump

Signal

KTA 75 mm

43% conversion to 1507 nm

5 kHz PRR


KTA and PPLN OPOs provide longer-wavelength IR

• Pump source: MOPA #2• KTA OPO

– 60-mm crystal length, 80-degree cut• 30 W pump, 5 kHz PRR• 10 W at 1530 nm, 3 W at 3340 nm

– 40-mm crystal length, 60-degree cut• 33 W pump, 5 kHz PRR• 5-6 W of idler tunable from 2300-3000 nm

• PPLN OPO– 19-mm crystal length, 30.8-um pitch

• 30 W pump, 5 kHz PRR• 5.2 W at 2610-nm idler, 3W at 1720-nm signal


Closing Comments

• The “next generation” solid state lidar transmitters will replace the lamp-pumped Nd-doped laser “engine” with a diode-pumped Nd-laser “engine”

• To be cost-effective (and reliable) the diode-pumped lasers should be cw-pumped and repetitively Q-switched

• A full range of nonlinear optics (harmonic generators, OPOs) and tunable lasers (Ti:sapphire, etc.) are usable with the cw-pumped “engines” to provide wavelength diversity and tunability

Advanced Solid State Lasers for Lidar Systems - Q … 1998.pdfJuly 9, 1998 Ilrc98.ppt KTP-family...

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