Diode-pumped, High-Power Nd:YLF and Nd:YVO4 Lasers

D. Lee, K.J. Snell, J.G. Manni, K.F. Wall,Y. Isyanova and P.F. Moulton

Solid State & Diode Laser Technology Review 20008 June, 2000

Albuquerque, NM

Outline

• Laser materials choices• Basic Nd:YLF laser design and performance• Basic Nd:YVO4 laser design and performance• MOPA systems• Applications

Three Nd Laser Hosts As Choices

Crystal Thermalconductivity

(W/m K)

Expansioncoeff.(10-6)

Thermalshock(W/m)

dn/dT(10-6)

Lensing

YAG 13 6.7 1450 +7.3 moderateYLF 5.8 (c)

7.2 (a)8 (c)13(a)

240 -4.3 (e)-2.0 (o)

weak

YVO4 5.2 7.3 (a)?? (c)

? +2.9 (e)+8.5 (o)

strong

Crystal Wavelength (nm)

Gain cross section

(10-19 cm2)

Lifetime(µs)

Peak absorption

(cm-1)YAG 1065 3.3 240 10YLF (π)YLF (σ)

10471053

1.9-2.3π / 1.5

480-520 11

YVO4 (π) 1064 9.8-15.6 97 40

MPS Pumping Design

Diode laser

Diode laser

Nd:YLF Lasercrystal

Cylinder lensLaserbeam

Pumpbeam

MPS gain module with resonator (MPS-1047)

AOQ-switch

Gain module

Diode Laser bar

Nd:YLF slab

Production data on MPS gain module

0.0

2.0

4.0

6.0

8.0

10.0

12.0

14.0

16.01 3 5 7 9 11 13 15 17 19 21 23 25 27 29

Gain module number

Pow

er o

utpu

t (W

)

Average: 12.1 WMedian: 12.1 WStandard deviation: 0.9 W

0

1

2

3

4

5

6

7

8

10.5 11 11.5 12 12.5 13 13.5 14 14.5

Power output (W)

Num

ber o

f mod

ules

MPS Q-switching produces high powers

100 1000 10000 100000

Pulse rate (Hz)

Peak

Pow

er

MPS-E

MPS

1 MW

100 kW

10 kW

1 kW

CW oscillator performance scales upward

0

5

10

15

20

25

30

35

40

0 10 20 30 40 50 60 70 80

Pump Power (W)

Out

put P

ower

(W)

40 W, MM30 W, MM30 W, TEMoo20 W, TEMoo

TEMoo properties are power-independent

0

0.2

0.4

0.6

0.8

1

1.2

1.4

35 40 45 50 55 60 65

Pump Power (W)

Bea

m D

iam

eter

(mm

)

0.95

1

1.05

1.1

1.15

1.2

1.25

1.3

M2

Horizontal Plane

Vertical Plane

Q-switched average power is nearly doubled with 50% more pump power

0

5

10

15

20

25

30

0.1 1 10 100

Pulse rate (kHz)

Ave

rage

pow

er (W

)

63 W40 W

Pumppower

Higher gain yields shorter pulses

0

50

100

150

200

250

300

10 20 30 40 50 60 70 80 90 100

Pulse rate (kHz)

Puls

ewid

th (n

s)

40 W63 W

Pumppower

Peak power is increased at high PRR

0.1

1

10

100

10 20 30 40 50 60 70 80 90 100

Pulse rate (kHz)

Peak

pow

er (k

W)

63 W40 W

Pumppower

High-power, MPV (Nd:YVO4) gain module

HR

HR

Collimated 20 WLaser Diode Bars

Nd:YVO4 Slab

MPV (Nd:YVO4 ) Oscillator CW Efficiency

0

2

4

6

8

10

12

14

16

0 10 20 30 40

Pump Power (W)

Out

put P

ower

(W)

1064 nm MM1064 nm TEMoo1342 nm TEMoo

• 1064 nm, >15 W multimode, >13 W TEM00, 46.3% slope, 35.0% optical and 13% electrical efficiency.

• 1342 nm, >6 W TEM00, 26% slope, 15% optical and 6% electrical efficiency.

MPS CW Amplifier Performance

• Gain of 17 with 27 mW input at a pump power of 38.7 W. 3-pass small signal gain >30 based on later single-pass measurements.

0

2

4

6

8

10

12

14

16

18

0 1 2 3 4 5

Input Power (W)

Gai

n

0

1

2

3

4

5

6

7

8

9

10

11

12

Out

put P

ower

(W)

GPo

MPS and MPV pulsewidth vs. rate

1

10

100

1000

1000 10000 100000 1000000

Pulse rate (Hz)

Puls

ewid

th (n

s)

MPS

MPV

MPS MOPA system #2 generates 50 W cw

EOQ-switch

Two-module Nd:YLF Oscillator1st StageAmplifier

2nd StageAmplifier

Cylinderlens

Cylinderlens50 W CW

40 W Q-Sw @ 5 kHz14-ns pulsewidth

MOPA #2 laser head

MOPA design allows scaling to 60 W cw

(20-W pump lasers)

50 W QS@ 5 kHz

60 W cw

GM

18 W

11 W10 W

GMIsolator QS

GM GM GM

28 W 40 W

Q-Switched, Nd:YLF, Master Oscillator

GM Gain ModuleRelay Optics

QSMirrors AO Q Switch

MOPA generates 54 W cw with one amplifier

(40-W pump lasers)

54 W cwwith 128 W total pumpM2 ≈ 1.1

MPV Nd:YVO4 MOPA System

Osc

AO Amp1 Amp2 Amp3Is

olat

orAmp4

Output

• 5 Gain Modules; 1 Oscillator, 4 Power Amplifiers. Same design for both 1064 nm and 1342 nm.

• Relay-imaged between master oscillator and amplifiers to preserve optimum beam size throughout the MOPA chain.

Nd:YVO4 MOPA Results

1064 nm• Outputs CW/Q-Switched @ 50 kHz

Oscillator: 11.4 W /10.5 W, 10 ns FWHMOutput: 53.5 W / 50.7 W, 10 ns FWHM, 1.01 mJ/pulse

101.4 kW Peak• 200 W pump power → >25% optical, >10% electrical efficiency.

1342 nm• Outputs CW/Q-switched @ 50 kHz

Oscillator: 11 W /9.6 W, 22 ns FWHM (Double crystal)Output: 26.5 W / 25.0 W, 22 ns FWHM, 0.5 mJ/pulse

23 kW Peak 240 W pump power → 10.4% optical, 4% electrical efficiency.

Nd:YLF harmonic conversion generates high visible, UV powers (with Ushio)

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

SHG (523.5 nm):30 W at 67 kHzand 60-68% conversionin LBO

3HG (349 nm):6 W at 10 kHz (30%)15 W at 5 kHz in LBO

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

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

3HGLBO

MPS-based 349-nm commercial product

A/O QS

Nd:YLF Oscillator Amplifier Gain Module

SHGLBO

THGLBO

1047 nm10 Watt

1047 nm20 Watt

1047 nm10 Watt

523 nm10 Watt

349 nm

1047 nmand523 nm

6 Watt

Schematic of RGB OPO

Type-IISHG LBO

Pump524 nm

Signal 898 nm +Green 524 nm

Red628 nm

Idler1256 nm

f = 29 mm

SWP: HR@ 1256 nm;HT@ 524, 628, and 898 nm

Intracavity SHG

Singly Resonant OPO Green524 nm

SWP

Signal898 nm

LWP

Walk-Off compensated

Type-I SHG LBO

Blue449 nm

Type-I OPO LBO

Watt-level doubled OPO outputs at 10 kHz

0

0.5

1

1.5

2

2.5

3

3.5

4

4.5

0 2 4 6 8 10 12

Green power (W)

Pow

er (W

)

SignalRedBlue

IR parametric oscillator systems

Intracavity OPO1 W output

at 1507 nm

12.5 kHz PRR

6 ns pulsewidthAO

Q-switch

Gain module

Diode Laser bar

Nd:YLF slab KTA 25 mm

External OPO

0

1

2

3

4

5

6

0 2 4 6 8 10 12 14

Pump power (W)

Sign

al p

ower

(W)

43% conversion to 1507 nm

5 kHz PRRQ-SW Pump

Signal

KTA 75 mm

Tuning curve for MPS-driven KTA OPO

0

1

2

3

4

5

6

2 2.1 2.2 2.3 2.4 2.5 2.6 2.7 2.8 2.9 3 3.1 3.2

Wavelength (um)

Pow

er (W

)

Tandem OPO design gives full IR coverage

MPS MOPAPump laser KTA OPO CdSe OPO

1.5 - 3.6 µm

3 - 12 µ m

Angle-Tuned NCPM

Results to date:(At 4 kHz pulse rate, 30-W pump power)

•KTA signal at 1514 nm: 6.5 W•KTA idler at 3450 nm: 5 W•CdSe signal at 5120 nm: threshold•CdSe idler at 10570 nm: threshold

MPS modules amplify a mode-locked laser

(Modules pumped by 20-W bars)

0.7 W,4.5 ps @100 MHz

Amplified ML laser converts efficiently

SecondHarmonic

Crystal

NCPMLBO

AmplifiedML laser

CPMCLBO

FourthHarmonic

Crystal

2.9 W at262 nm

15.0 W at1047 nmM2 < 1.1

8.4 W at523.5 nmM2 < 1.1

MPV amplifies a micro-chip laser

HR mirrorFaraday rotator3 mW at 2 kHz, 400 ps pulsewidth

650 mW MPV gain moduleNd:YAG / Cr:YAGmicrochip laser

at 1064 nmNCPM LBO

SHG

390 mW, 2 kHz PRR at 532 nm

Summary

• Side-pumped Nd:YLF MPS and Nd:YVO4 MPV designs combine simplicity, scalability of side pumping with the high-efficiency, TEM00-mode performance of fiber-coupled, end-pumping designs.

• Recent availability of 40-W bars has more than doubled the output of MPS Nd:YLF “gain module” to > 25 W and increased peak power at high pulse rates. Nd:YVO4performance may improve as well, but strong thermal lensing will be a challenge.

• CW-pumped, Q-switched systems can efficiently drive nonlinear optics to generate tunable, vis-UV and IR wavelengths.

• Systems designers should consider cw-diode-pumped systems instead of pulsed-pumped systems for cost and reliability reasons.

Diode-pumped, High-Power Nd:YLF and Nd:YVO4 LasersOutlineThree Nd Laser Hosts As ChoicesMPS Pumping DesignMPS gain module with resonator (MPS-1047)Production data on MPS gain moduleMPS Q-switching produces high powersCW oscillator performance scales upwardTEMoo properties are power-independentQ-switched average power is nearly doubled with 50% more pump powerHigher gain yields shorter pulsesPeak power is increased at high PRRHigh-power, MPV (Nd:YVO4) gain moduleMPV (Nd:YVO4 ) Oscillator CW EfficiencyMPS CW Amplifier PerformanceMPS and MPV pulsewidth vs. rateMPS MOPA system #2 generates 50 W cwMOPA #2 laser headMOPA design allows scaling to 60 W cwMOPA generates 54 W cw with one amplifierMPV Nd:YVO4 MOPA SystemNd:YVO4 MOPA ResultsNd:YLF harmonic conversion generates high visible, UV powers (with Ushio)MPS-based 349-nm commercial productSchematic of RGB OPOWatt-level doubled OPO outputs at 10 kHzIR parametric oscillator systemsTuning curve for MPS-driven KTA OPOTandem OPO design gives full IR coverageMPS modules amplify a mode-locked laserAmplified ML laser converts efficientlyMPV amplifies a micro-chip laserSummary