Laser Applications to Chemical, Security, and Environmental Analysis

San Diego, CA1 February 2010

Characterization of Highly Stable Mid-IR, GaSb-Based Laser Diodes

A. V. Okishev,1 D. Wang,2 D. Westerfeld,3 L. Shterengas,2 and G. Belenky,2University of RochesterLaboratory for Laser Energetics1Laboratory for Laser Energetics 2SUNY at Stony Brook3Power Photonics Corp

60

50

40

30

20

10

01000 1400

12ºC

3150 nm

3181 nm

1800 2200 2600

Driver current (mA)

Ou

tpu

t p

ow

er (

mW

)

A new highly stable mid-IR laser diode has been characterized

E18591

• Mid-IRlaserdiodesarerequiredforcryogenicD2 target layering for Inertial Confinement Fusion (ICF).

• Room-temperaturemid-IR,GaSb-basedlaserdiodeshavebeencharacterized at various temperatures and driver currents.

• Upto54mWofoutputpowerwasdemonstratedina3150-to3180-nmwavelength range with <20-nm FWHM spectral width.

• Highspectralandoutputpowertemporalstability(<1% rms) has been demonstrated.

• Upto37mWofoutputpowerisavailableforcryogenicD2 target layering.

Summary

Laserdrive D2-fuel-filled

pellet

Implodingpellet

Expandingblowoff

2. Compression

1. Irradiation

3. Thermonuclear ignition

Compressedpellet

Tem

per

atu

re

Radius

Mas

s d

ensi

ty

Hot spot

Burnwave

Ablator

Main fuel –D2 ice

D2 gas

Ablationisusedtogeneratetheextremepressuresrequiredto compress a fusion capsule to ignition conditions

S5v

“Hot-spot”ignitionrequiresthecoretemperaturetobeatleast10keV and the core fuel areal density to exceed ~300 mg/cm2.

Cryogenic D2targetlayeringrequiresastablemid-IR source

E17940

• Themid-IRsource’soutputpowerandspectrummustbetemporallystable to avoid overheating and melting the ice layer.

• Otherapplicationsincludegassensing,spectralanalysis,infraredillumination, countermeasures, and medical diagnostics.

Unlayered target

Sphericalisotherm

Layered target

Layeringsphere

0.9-mm-diam target at ~18.7 K in a layering sphere

Mid-IR lasersource output

Temperaturegradient

Mid-IRlaser-sourcerequirementsforcryogenic D2 target layering

E18592

• Centralwavelength 3160nm• Centralwavelengthstability ±2 nm• Spectralwidth 5< Dm < 20-nm FWHM• Centralwavelengthtuningrange ±15 nm• Outputpower 10to100mW(for ~1-mm target size)• Operatingregime Continuouswave

0.6

log

10(I

0/I) 0.4

0.2

0.03000 3200

Frequency (cm–1)

Solid D2 1.9 K,2.5 mm path

3400

D2 absorption band*is well approximatedwith4thordersuperGaussian

*A. Crane and H. P. Gush, Can. J. Phys. 44,373(1966).

GaSb-based mid-IR diode lasers manufactured at SUNY – Stony Brook present an attractive light source for D2 target layering

E18037

Quantum wells(In0.54Ga0.46As0.23Sb0.77)

p-clad(Al0.6Ga0.4As0.05Sb0.95)

Waveguide(Al0.2In0.2Ga0.6As0.02Sb0.98)

n-clad(Al0.6Ga0.4As0.05Sb0.95)

Ec

Ev

Band structure of 3-nm laser diode*(Ec – the bottom of conductive band; Ev – the top of valence band)

*L. Shterengas et al., Appl. Phys. Lett. 92,171111(2008).

Output power and spectra have been measured for three laser diodes

E18288

60

50

40

30

20

10

0

1.0

0.8

0.6

0.4

0.2

0.01000 1400 1800 2200 2600

Driver current (mA)

Ou

tpu

t p

ow

er (

mW

)

No

rmal

ized

sp

ectr

alin

ten

sity

Diode #1Linear (diode #1)Diode #2Linear (diode #2)Diode #3Linear (diode #3)

12°C

3130 3140 3150 3160 31803170 3190

Wavelength (nm)

12°C1600 mA

Diode #1Diode #2Diode #3

Laser diode #1 has been chosen for further testing due to higher output power and a more compact symmetric spectrum.

Output power of diode #1 depends on driver current and temperature

E18289

10

20

30

40

50

60

01200 1600 2000 2400

24

1620

12

Ou

tpu

t p

ow

er (

mW

)

Driver current (mA)

Temperature(°C)

mW50403020100

Output beam profile(60º × 12º divergence)

Output spectral shape and central wavelength change with temperature and current

E18290

D2 absorption must be taken into account when the laser-diode working point is specified for D2 target layering.

60

50

40

30

20

10

03130 3150 3170 3190

Wavelength (nm) Wavelength (nm)

~2 nm per ºC(7.5ºC temp tuning is requiredfor 15-nm wavelength tuning)

~2.5 nm per 100 mA

1600 mA

20

0

40

60

50

30

10

70

31503130 3170 3190

12ºC

Sp

ectr

al in

ten

sity

(arb

itra

ry u

nit

s)

Sp

ectr

al in

ten

sity

(arb

itra

ry u

nit

s)

1200 mA1400 mA1600 mA1800 mA

2000 mA2200 mA2400 mA

12ºC14ºC16ºC18ºC

Thediode#1spectrumishighlystableandfitswell with the D2 absorption band

E18295

Diode #1 output-power stability is <1% rms over two hours of operation.

31300

10

20

30

40

50

60

70

80

3140 3150 3160 3170 3180 3190

0.5

0.0

1.0

Wavelength (nm)

10 spectra takenover 2 hours

Sp

ectr

al in

ten

sity

(ar

bit

rary

un

its)

Mo

del

ed D

2 ab

sorp

tio

n

1600 mA 1800 mA

12°C

Diode#1produces37mWofoutputpowerat1800mA and 12ºC that perfectly fit D2 absorption spectrum

E18593

8

24

16

32

40

0

Ab

sorb

ed p

ow

er (

mW

)

12001600

20002400

Driver current (mA)

16

12

Temperature(°C)

mW40

32

24

16

8

0

A new highly stable mid-IR laser diode has been characterized

E18591

• Mid-IRlaserdiodesarerequiredforcryogenicD2 target layering for Inertial Confinement Fusion (ICF).

• Room-temperaturemid-IR,GaSb-basedlaserdiodeshavebeencharacterized at various temperatures and driver currents.

• Upto54mWofoutputpowerwasdemonstratedina3150-to3180-nmwavelength range with <20-nm FWHM spectral width.

• Highspectralandoutputpowertemporalstability(<1% rms) has been demonstrated.

• Upto37mWofoutputpowerisavailableforcryogenicD2 target layering.

Summary/Conclusions