Multi-Watt Single Frequency Output from 1.4 to 4.2 Microns (2400 to 7100cm-1) from a

Single Laser System

Angus Henderson, Paul Hoffman and Ryan Stafford

Aculight CorporationBothell, WA

6/21/07

Practical laser sources for spectroscopy scarce in 2 to 4m region

• Lead salt lasers – low power, poor spectral quality, cryogenics

• DFG sources – low power

• Diode lasers – mostly below 2m

• Quantum cascade lasers – not below 4m

ArgosTM is a single frequency CW OPO pumped by a 15 Watt fiber laser

OPO

Fiber-collimator

PPLNOven

PZT

M1 M2

PumpFilter

EtalonET2 M3M4

UnconvertedPump

i

Yb fiber laserOPO tuning

controller

Control unit and OPO head

OPO systemconfiguration

OPO produces two highpower SLM outputs

isp 111

signal

idlerpump

periodically polednonlinear material

OPO inputmirror

Partially reflectiveOPO output mirror

.

0

2

4

6

0 2 4 6 8 10 12 14 16

Idler power Signal power

Pump power (Watts)

Idle

r a

nd

sig

na

l po

we

r (W

att

s)

Signal 1660nm, idler 2950nm

Power vs wavelength

Idler wavelengthsSignal wavelengths

Wavelength modules are interchangeable with same pump laser

Short term linewidth < 60kHz (2*10-6 cm-1)

• Beat frequency measured between two OPOs tuned to 2930nm

• Timescale 500 microseconds

• Same measurement gives 600kHz linewidth over 80 ms

< 30 MHz over 2 minutes

• Frequency stability measured by “parking” frequency on an N2O line at 2984nm

< 30 MHz over 2 minutes

Mode-hop-free operation over 14 hours

• 30pm variation in 14 hours – driven by temperature

• No mode hops once equilibrium temp. reached

• No active feedback or cavity temp. control

• 150MHz stability over 10 hours with cavity temp. control

-0.50

-0.25

0

0.25

5 10 15 20

14 hours w/o mode-hops

Time (Hours

Wa

vele

ng

th d

evi

atio

n (

nm

)

3% pk to pk power stability over 24 hours

0

1

2

3

4

5

0 5 10 15 20

Time (Hours)

Idle

r p

ow

er

(Wa

tts)

3010nm idler power stability over 24 hours

Sdev 0.6%

Coarse tuning ~700nm tuning via poling period

• OPO poled with fan-out pattern – period varies linearly across crystal

• OPO tunes by translating crystal relative to pump beam

• Temp tuning also allows coarse tuning

2300

2450

2600

2750

2900

3050

40 80 120 160

Crystal lateral position (A.U.)

Wa

vele

ng

th (

nm

)

Intermediate tuning - Etalon tunes ~9nm through adjacent free spectral ranges

2988.000

2990.000

2992.000

2994.000

2996.000

2998.000

3000.000

3 3.5 4 4.5 5 5.5

Etalon Display Reading (deg)

Idle

r W

avel

eng

th (

nm

)

Tuning by galvo rotation of intracavity etalon

Fine mode-hop-free tuning by temperature or PZT tuning of fiber seed laser

+

i

Nonresonant wave tuning of singlefrequency pumped OPOs

sp

Fiber amplifier

Bulk Isolator

Fiberisolator

Fiberconnector

DFB fiber laser

Etalon

Mid-IRoutput

MgO:PPLN

OPO idler tunes synchronously with pump

• DFB fiber laser is default seed• Alternate seeds can be used e.g. DBR diode

Fine tuning allows rapid spectral scans

0.00

0.05

0.10

0.15

0.20

0.25

0.30

3558.2 3558.4 3558.6 3558.8 3559 3559.2

Wavenumber (cm-1)

Ab

sorb

ance

CO2

Data obtained in single sweep,

30ms

Photoacoustic spectra with 16kHz frequency modulation using DBR diode seed

-60

-40

-20

0

20

40

60

80

-4 -3 -2 -1 0 1 2 3 4

060129_8&9

#8, more NH3#9, less NH3

X

Current, a.u.

3367.642 H2O

3367.519 H2O

3367.470 NH3

3367.377 NH3

Beam profile – close to diffraction limit

0.1

0.2

0.3

0.4

0.5

-60 -30 0 30 60

Y axis: y=sqrt(a2+b

2*(((3.037*10

-3)

2/(3.14159*a)

2))*(x-c)

2) max dev:0.0203, r

2=0.992

a=0.133, b=1.03, c=-0.709

X axis: y=sqrt(a2+b

2*(((3.037*10

-3)

2/(3.14159*a)

2))*(x-c)

2) max dev:0.0227, r

2=0.985

a=0.143, b=0.983, c=-3.80

Position (mm)

Ra

diu

s (m

m)

Radius v Position Bmod 1W 3037nm

Wavelength extension – sum frequency generation and second harmonic generation

• Intracavity signal power is 100s of Watts

• SFG (signal + pump) produces ~0.3mW 600 to 700 nm

• SHG (signal) produces >1mW 700 to 1000 nm

• SHG of idler produces 1000 to 1400nm

• All single frequency outputs

-60

-40

-20

0

750 1000 1250 1500 1750

Signal+pumpSFG Signal

Pump

Signal SHG

Wavelength (nm

Po

we

r (d

Bm

)

Future – CW OPO using OP-GaAs

• Collaboration with Stanford U.

• Can be pumped by Erbium or Thulium fiber laser

• Transparent out to 16 m

1.80 1.85 1.90 1.95 2.00 2.05

2

3

4

5

6

7

8

9

10GaAs, QPM period=61.2 m

sign

al &

idle

r (

m)

pump (m)

Conclusion: OPO is a robust, powerful source for near to mid-infrared spectroscopy

• Provides multi-Watt level power in both near-IR and mid-IR

• Single frequency output at signal and idler

• Mode hop free tuning of ~60GHz

• Near-diffraction-limited beam quality

• Stable in power and frequency

• Fiber laser provides robust pump source

Aculight CW OPO product

Demo unit running at Aculight booth