High Power Diode Lasers - Center for Biomedical Optics and New ...

Bio-Photonics ’03 Summer School 

High Power Diode Lasers 

Fabrication 

Characterization 

Results in the near IR (732-980 nm) 

Applications 

Michel Krakowski 

Sophie-Charlotte Auzanneau 

Thales Research and Technology France

Fabrication 

•Materials 

• Epitaxy 

• Process 


Laser diodes 

• power and spectrum measurement 

• far-field and near-field measurement 

• The M² factor : definition, measurement 

• Saturation of the power : cause and solution = the large optical cavity 

Main epitaxial structures : at 808 nm, 940 nm, 980 nm and 732 nm 

Examples of lasers diodes 

• Ridge and broad-area lasers at 980 nm 

• high brigthness lasers near at 980 nm 

• state of the art 

• external approach : four-wave mixing 

• internal approach : the tapered laser diode 

• Tapered lasers bars at 980 nm coupled into an optical fiber 

• Laser diodes at 732 nm : broad-area laser results and aging test 

• Application to photodynamic therapy of laser diodes at 732 nm 

• Application to surgery and dentistry of laser diodes at 980 nm

How is a laser diode 

Max. size : 3 mm long 

and 100-200 µm large 

On Indium 

18 Au wires 

Laser 

6 mm 

Output 

facet 

Laser 

Alumina 

3 mm 

Copper holder

Schematic of a laser diode = stack of semiconductor materials 

layers 

Anti-reflection 

coating (AR 3%) 

100-200 µm 

High 

reflection 

coating 

(HR 95%) 

2- 3mm 

Electrodes 

Confinement 

layers 

Separated 

confinement layers 

Cleaved facets 

Current injection 

Photon guiding 

Optical losses are 

reduced 

Mirrors 

Active region 

Lateral passivation 

Photon generating 

Electrical isolation

Which material system for which wavelength 

II-VI compounds 

Diode lasers 

GaN/AlInGaN 

GaAs/GaInAs/GaAlAs 

GaAs/GaInAsP 

InP/GaInAsP 

0 

0 0.5 1.0 1.5 

2.0 

Wavelength ( µm) 

GaSb/ 

AlGaInSbAs 

Quantum Cascade lasers 

GaAs/AlGaAs 

GaInAs/AlInAs/InP 

THz and 

mm wave 

0 

0 5 10 15 20 

Wavelength ( 

µm)

Steps of the fabrication of a laser diode 

1- SUBSTRAT (wafer) 2- EPITAXY : growth of layers 3- LASER PROCESSING 

4- FACETS CLEAVING 5-chip cleaving 

6- MOUNTING, BONDING 

A 2’’ wafer ≈ 1000-2000 chips

substrate 

Schematic of the growth of semiconductor layers 

Dissociated 

molecules 

Dissociated 

molecules

Layers growth : 2 kinds of epitaxy 

MBE : Molecular Beam Epitaxy 

MOCVD : Metallo-Organic 

Chemical Vapor Deposition 

Molecules fluxes, with ≠ rates 

Gas fluxes, with ≠ rates 

Wafer en 

rotation 

400-500° 

Dissociated 

molecules 

Unused 

gas 

Rotating wafer ∼ 

650° 

Liquid or solid sources 

Gas sources

Layers growth : 2 kinds of epitaxy 

MBE : Molecular Beam Epitaxy 

MOCVD : Metallo-Organic 

Chemical Vapor Deposition 

slow growth : good controle of the 

interfaces quality atomic layers. 

ultravacuum (10 -10 Torr) 

Controle in-situ of the thicknesses of the 

layers (diffraction X) 

A usual laser diode = 6h 

Quantum cascade laser diode = 40h 

Machines : Riber, Varian (en salle 

blanche)…. 

No phosphide. 

faster growth : layers thicker 50-70 nm 

(no quantum cascade laser). 

under weak pressure or ambiant pressure. 

A usual laser diode = 5-6h 

Machines : Aixtron (white room)…. 

phosphore allowed. 

organo-métallic = gas giving elements III 

( Triméthyl In, Ga, Al…) 

Arsine (As), phosphine (P), Silane (Si) : 

toxiques 

1 epitaxy machine = a small truck

Si 3 N 4 , SiO 2 

Process : why 

To define a surface where the current is injected 

Typical threshold current density of a laser diode J th 

~ 100 A/cm 2 to 1 kA/cm² 

To minimize it, we reduce the injection surface! 

Active region 

contact 

~ 

Substrate 

~ 

process 

~ 

Substrate 

~ 

EPITAXY 

size = 1 - 100 

mm 

Laser surface = 1 cm 2 I th = 100A to 1000 A ! 

Laser surface = 100 µm x 1 mm = 10 -3 cm 2 

I th = 100 mA to 1 A

Process 

Three steps of the planar process 

Photolithography 

Masquage et 

Insolation UV 

Développement 

et ouverture 

Etching 

Ionic etching (dry etching) 

Chemical etching 

Coating 

(metallic and dielectric)

Then mounting on copper holder … 

p-down 

p-up 

N side 

xxxxxxxxx 

xxxxxxxxx 

P side 

xxxxxxxxx 

soldering 

xxxxxxxxx 

P side 

soldering 

N side 

current 

Thermal regulation (Peltier) 

current 

Thermal regulation (Peltier) 

The heat is well dissipated because 

the active region is near the 

thermal regulation 

For specific technologies 

high power laser diodes

And electrical wires soldering … 

Scale : the micron !! 

Now we can characterize the laser diode ... ha ha ha ...

Fabrication 

•Materials 

• Epitaxy 

• Process 


Laser diodes 
















The laser diode : assymetric device elliptic 

beam 

Perpendicular (fast) axis 

Near-field (µm) 

∼ 1 µm 

Diode laser 

θ y 

cavité optique 

θ x 

HR 

AR 

Parallel (slow) axis 

Far-field 

(rad) 

We characterize 

according to each axis (no 

correlation) 

In the ⊥ direction, monomode 

beam. In the // direction, it’s 

different …

Polarization of a laser diode 

Point for electrical 

contact 

With a p-down laser 

diode : 

Pol. - 

Pol. + 

Thermal regulation

• power measurement : high divergence of the beam 

⇒ we use a sphere. 

z 

Laser diode 

Photodiode : 

power 

calculation 

Thermal 

regulation 

+ 

spectrometer 

for λ

• Near-field measurement 

Microscope objective 

Laser diode 

CCD camera 

z 

Beam analyser 

Camera linked 

to a PC (beam 

analyser)

• far-field measurement 

Laser diode 

Diverging beam 

Rotating 

photodiode 

0.0 

-20 

power 

0.2 0.4 0.6 0.8 1.0 

θ 

z 

a 

n 

g 

l 

e 

-10 

0 

10 

θ 1/e² 

θ 1/2 

20 

θ

Brightness 3D (W.cm 

- 2 

.sr 

-1 

) = 

Luminance (brightness) 

emissive 

OpticalPower (W) 

area (cm²) * solid 

angle 

(sr) 

Brightness 

1D 

-1 -1 

(W.cm .rad ) 

= 

Perpendicular 

(fast) axis 


W (cm)* θ (rad) 

Near- 

field 

∝ 


M 

² 

1D 

Laser diode 

θ y 

W x 

Optical cavity 

θ x 

Parallel (slow) axis 

Luminance ⇒ spatial beam quality ⇒ M² ⇒ near-field size and far-field 

angle of the beam. 

Far- 

field

W(z) = 

W 

W(z) 

0 

⎛ 

1+ 

⎜ 

⎜ 

⎝ 

The Gaussian beam 

2 

⎞ 

M2λ(z 

− z0) 

⎟ 

2 ⎛ π ⎞ 

M = ⎜ ⎟θ 

W > 1 

2 ⎟ 

1/e² 01/e² 

πW0 

⎝ λ ⎠ 

⎠ 

0 

1 

Waist : 2 w 0 

z 

2θ 

1.0 

0.8 

0.6 

0.4 

0.2 

0.0 

-20 -10 0 1 

Taille u.a. 0 

W 0 1/e² 

2 

0 

Near-field at the waist -20 -10 0 10 20 

Ref. : A.E.Siegman, « New developments in laser resonators », SPIE Vol. 1224, 1990 

u.a. 

1.0 

0.8 

0.6 

0.4 

0.2 

0.0 

Divergence u.a. 

Far-field 

θ 1/e²

What is the limitation of the emitted power 

• Diode heating : power saturation , normally 

non-destructive (thermal roll-over) 

400 

350 

300 

250 

P (mW) 

200 

150 

100 

• Catastrophic optical mirror damage (COMD) : 

destructive 

50 

0 

0 200 400 600 800 1000 

I (mA) 

BC 

BV 

hν 

Recombinaison non-radiative 

électron-trou de surface 

Elévation de température 

Réabsorption optique 

COMD 

Face-miroir 

Filamentation

• Catastrophic optical mirror damage (COMD) : destructive 

Maximal emitted power: 

P 

MAX 

(mW / 

µm ) 

= P ( λ) 

COMD 

1−R 

. 

1+ 

R 

d 

Γ 

PCOMD: internal optical power density at threshold COMD 

R: mirror reflectivity 

d: active region thickness (reabsorbing) 

Γ: overlap of the transverse mode with the active region 

d : transverse spot size 

Γ 

Active-Region material P COMD (MW /cm 2 ) 

InGaAs (0.92 - 0.98µm) 18-19 

InGaAsP (0.81µm) 18-19 

InAlGaAs (0.81µm) 13-14 

GaAs (0.81 - 0.87µm) 10-12 

Al 0.07 GaAs (0.81µm) 8-9 

Al 0.13 GaAs (0.78µm) 5 

(Botez, SPIE proceedings, vol. 3628, p5, 1999) 

To increase P max : 

>Structure design: 

- enlarged guides 

>Active region materials: 

-InAlGaAs 

- InGaAsP (Al-free)

Laser diode with an enlarged active region : advantages 

Wider transverse near-field (> 0.5 µm) : COMD level increased. 

Weak internal losses (< 1 cm -1 ): 

High external differential efficiency 

Longer cavity are possible (> 1 mm): thermal and electrical 

resistivities are decreased 

Power and efficiency record in CW 

Usual cavity 

(Thershold current minimized) 

1,0 

Enlarged cavity : 

Γclad => α 

Γqw => COMD 

Refractive index, Near field intensity 

p Cladding 

QW 

QW 

nid waveguide 

n Cladding 

Refractive index, Near field intensity 

0,8 

0,6 

0,4 

0,2 

0,0 

-0,2 

QW 

p Cladding 

nid Broad Waveguide 

n Cladding 

-4 -2 0 2 4 

Distance 

Distance

Fabrication 

•Materials 

• Epitaxy 

• Process 


Laser diodes 
















Laser structure 732 nm : 

GaAsP / AlGaAs / AlGaAs 

• Tensile strained GaAsP QW 

TM polarisation 

• High Al – content 

of waveguide and cladding layers 

• LOC structure (1µm waveguide)

Fabrication 

•Materials 

• Epitaxy 

• Process 


Laser diodes 















• Application to surgery and denistry of laser diodes at 980 nm

All the results presented here have been 

obtained in the IST-1999-10356 european 

project ULTRABRIGHT 

Reliable Ultra-Bright Laser Diode Sources 

For Terabit Telecommunications 

and Photodynamic Therapy Applications 

Results from : 

Thales Research and Technology (TRT) 

Thales Laser Diodes (TLD) 

Ceram Optec 

Ferdinand-Braun-Institut für Höchstfrequenztechnik 

R&T 

CeramOptec GmbH

Why a high brightness laser diode at 980 nm 

Laser with a GaInAs quantum well on GaAs 

substrate. 

Losses on the 1.55 µm signal in the optical fibers 

1.55 µm signal 

Erbium 

doped fiber 

pump 

Erbium 

Ion 

optical amplification with the EDFA 

(Erbium Doped Fiber Amplifier)

How can we bring more power in the optical 

fiber 

Efficient coupling of the emitted power in the optical fiber 

Pump diode 

Coupling optics 

Optical fiber 

⇒ that’s why we need : high power + high beam 

spatial quality 

= high brightness

12 

11 

10 

CW optical power records delivered by 

single 100µm wide emitters at 25°C 

30/06/00 13:35:35 

Max. optical power (W) 

9 

8 

7 

6 

5 

4 

3 

2 

(55 µm) 

GaAs/AlGaAs : Mitsui Chemicals, Jap. 

Al-free : Wisconsin U./ Coherent USA 

AlGaInAs/AlGaAs : Optopower Corp. USA 

AlGaAs : SDL, USA 

AlGaAs : Fraunhofer Inst., Ger. 

GaAsP/AlGaAs : F. Braun Inst., Ger. 

GaAs/AlGaAs : Thales TLD 

Al-free : Thales TRT 

720 740 760 780 800 820 840 860 880 900 920 940 960 980 1000 

Wavelength (nm)

In the perpendicular direction : quasi-gaussian 

far-field profile (M² close to 1) for all the 

lasers fabricated with the same epitaxy. 

1,0 

I (u.a.) 

0,5 

0,0 

-60 -30 0 30 60 

Angle (°) 

θ 1/e² ≈ 52-65° 

But in the parallel direction, it depends on the 

waveguide shape …

In the parallel direction : 2 main kinds of lasers 

The broad-area laser : high power (∼10W at 0.98µm) but low beam spatial quality 

100 

µm 

1.0 

2 mm Far field 

P = 1 W 

M² = 15-20 

I (u.a.) 

0.8 

0.6 

0.4 

0.2 

0.0 

-15 -10 -5 0 5 10 15 

Angle (°) 

8,7° 

9,8° 

in the // 

direction 

The ridge laser: high spatial beam quality but a few hundreds of mW 

5 

µm 

2 mm 

P =300 mW 

M² = 1.2 

I (u.a.) 

1.0 

0.8 

0.6 

0.4 

0.2 

0.0 

-15 -10 -5 0 5 10 15 

Angle (°) 

8° 

14° 

Far field 

in the // 

direction

The broad-area laser 100 µm large * 2mm long : 

The broad-area laser 0.98µm AR/HR 100 µm * 2mm: 

8.5W CW, (usually operating at 3-4 W) 

Threshold : 340mA (170 A/cm²) 

Efficiency : 0.95W/A 

Mondial Record : 10.6W CW (Botez, U Wisc.) 

I (u.a.) 

1,0 

0,8 

0,6 

0,4 

// Far-field 

at 1W 

// 

2.5 

10 

1.0 

0,2 

Voltage U /V 

2.0 

1.5 

1.0 

V 

P 

eff 

. 

9 

8 

7 

6 

5 

4 

3 

Optical Power P /W 

0.8 

0.6 

0.4 

Efficiency η 

C 

I (u.a.) 

0,0 

-15 -10 -5 0 5 10 15 

1,0 

0,8 

0,6 

0,4 

Angle (°) 

// Near-field 

at 1W 

// 

0.5 

2 

1 

0.2 

0,2 

0.0 

0 

0 2 4 6 8 1 0 

C u rre nt I /A 

0.0 

0,0 

0 40 80 120 160 200 240 

x (µm) 

At 1W , parallel M² > 15 …

The broad-area laser 100 µm large at 980 nm : 

reliability 

PROFIL DE VIEILLISSEMENT TGB 969 P= 1W I=1.4A à 30°C 

PUISSANCE OPTIQUE (W) 

1.60 

1.40 

1.20 

1.00 

0.80 

0.60 

0.40 

0.20 

0.00 

0 1000 2000 3000 4000 5000 6000 7000 8000 9000 10000 11000 12000 13000 14000 15000 16000 

TEMPS CUMULE (HEURES) 

1-4 1-6 1-7 1-8 1-9 2-5 2-7

The broad-area laser 100 µm large at 808 nm : 

reliability 

1.60 

PROFIL DE VIEILLISSEMENT TGB963D A 1W, 1,4 A, 40°C 

Puissance optique (W) 

1.40 

1.20 

1.00 

0.80 

0.60 

0.40 

0.20 

0.00 

0 1000 2000 3000 4000 5000 6000 7000 8000 9000 10000 11000 12000 13000 14000 15000 16000 17000 18000 19000 20000 21000 22000 23000 

Temps cumulé (heures) 

8-2 8-8 9-1 9-2 9-4

The ridge laser 5 µm large * 2mm long : 

1,0 

Laser ridge 0.98µm AR/HR 5µm * 2mm: 300 W 

CW, (usually operating at 100-300 mW) 

Threshold : 40mA 

Efficiency : 0.95W/A 

Record : 1.2W (with optimized mirrors treatments) 

I (u.a.) 

0,8 

0,6 

0,4 

0,2 

// Far-field 

at 300 mW 

// 

300 

250 

0,0 

-25 -20 -15 -10 -5 0 5 10 15 20 25 

angle (°) 

P (mW) 

200 

150 

100 

I (u.a.) 

1,0 

0,5 

// 

// Near-field 

at 300 mW 

50 

0 

0 50 100 150 200 250 300 350 400 450 

I (mA) 

0,0 

28 32 36 40 44 

x (µm) 

At 300 mW , parallel M² =1.2

Others solutions to improve the brightness (1) : 

internal approach 

MOPA 

1 mm 

Laser (straight section with a 

Bragg grating) 

R 2 =0.01% 

- 1.5W FWHM// 0.26° Ortel IEEE- 

PLT 99 

- Difficulties: 

•R 2 ≈ 0.01% 

• interaction between the 2 sections 

I 1 I 2 

Master Oscillator Power Amplifier 

Tapered amplifier 

section 

• p-down mounting is difficult 

α- DFB 

I 

- 0.94 W FWHM// 0.2° SDL 

CLEO-97 

- 14 éléments bar, 20 W 75 A, 

FWHM// 1.1° , SDL CLEO-97 

- weak wall-plug efficiency 

- difficult fabrication


internal approach 

The index guided tapered laser bar 

30 µm 

15 µm 

- 8W 10A, FWHM// 5° à 4.5W, 

R 2 =1%, GEC EL-99 

200 µm 1800 µm 

The gain guided tapered laser 

100 µm 1900 µm 

- 2.2 W 4 A FWHM// 0.24° M²=2.2, R2= 0.05%, 

θ 200 µm 

Fraunhofer SPIE-98 

- 25 lasers bar, 25W 50A, M²=2.6 / emitter, 

Ipol 

Monomode lateral section : 

ridge 

Fraunhofer IEEE-PTL99


external approach 

Risø National Laboratory 

Optics & Fluid Dynamics Dept. 

Improving the Spatial and Temporal 

Coherence of High-Power Diode Lasers 

Using Four-Wave Mixing in the Gain Material 

Paul M. Petersen 

Optics and Fluid Dynamics Department, Risø 

National Laboratory, 

DK-4000 Roskilde, Denmark 

P.M. Petersen et al.

Others solutions to improve the brightness (3) : external approach 



New Laser design at Risø National Laboratory 

Gain- and refractive index gratings in broad area laser 

diodes 

may be used for selective amplification of spatial modes 

The effect is based on spatial hole burning in the active 

semiconductor gain material. 

The third order nonlinear susceptibility and the mode 

suppressions factor depend on the angle between the 

interacting beams in the four-wave mixing. 

A narrow range of angles exist with strong gratings and 

good mode suppression. 





Gain- and refractive index gratings in laser diodes 

0 

L 

Z 

Gain and refractive 

index gratings 

A 1 

A 3 

Semiconductor 

amplifier 

A 2 

Electrode 

Z=0 

Z=L 

The induced gain- and 

refractive index 

gratings lead to 

selective amplification 

of one spatial mode 

and suppression of all 

other modes 


Semiconductor 

amplifier 

and refractive 

Gain 

index gratings 




Four-wave mixing in diodes using spatial hole burning 

High reflective 

coating 

A 1 

0 

Z=0 

A 3 

A 2 

Electrode 

L 

Z 

Z=L 

Antireflection 

coating 

Spatial- and temporal 

filtering 

M 

Output 

beam 

The induced gratings 

eliminate filamentation 

and lateral lasing in the 

laser diode. 





Far-field profiles 

Intensity [arb. units] 

0 

1.4 times the 

diffraction limit 

Single- lobe 

80% of the total 

power is contained in 

a diffraction limited 

output lobe. 

0 

0 

-5 -4 -3 -2 -1 0 1 2 3 4 5 

Radiation angle [deg] 

Runs freely 





Singlemode 

(a) 

Single-mode 

operation 

BW < 0.02 nm 

Wavelength 

is tunable 

over 20 nm ! 

Intensity [arbitrary units] 

807 808 809 810 811 812 813 814 

Wavelength [nm] 

(b) 

(c) 

(d) 

(e) 


Other solution to improve the brightness at 980 nm developed in 

Thales Research and Technology (4) : the tapered laser diode 

Between power (broad-area laser) and spatial beam quality (ridge laser) 

Straight section (ridge) 

High reflection 

(HR) 

Tapered section 

θ 

Anti-reflection 

coatings (AR) = 

3% 

output 

Ridge 

L1 

Tapered sec. L2 

2-3 mm

Between the broad-area laser and the ridge: 

the tapered laser 

200 µm 2300 µm 

// Far- field at 600 mW 

1,0 

P (mW) 

1000 

800 

600 

400 

200 

To have more power : bars 

To obtain a lower divergence : tapered laser bars. 

• Broad- area laser bars (8 lasers) : P = 20W CW (for coupling into a 

multimode fiber). 

• Index guided tapered laser bars : P = 20W CW at 33A 

25°C 

Is : 4,8 A Rdt : 0.7W/A Eff. : 41% λ = 974 nm 

TOP VIEW 

TILTED FRONT VIEW 

ridge tapered section Single emitter output facet

Index guided tapered lasers bar 

Mini-bar width = 3 mm 

20 W, 33 A, 25°C, CW 

Is : 4.8 A Eff. : 0.7 W/A max Wall Plug Eff. : 41% 

Eff. 

P 

V 

At 33A λ = 974.5 nm and FWHM < 5 nm

Mini-bar of narrow index guided tapered lasers 

At 20 W, 33 A, 25°C, CW 

⊥ direction 

θ 1/2 = 31° 

θ 1/e² = 55° 

Intensity (a.u.) 

1,0 

0,8 

0,6 

0,4 

0,2 

// direction 

θ 1/2 = 3,5° 

θ 1/e² = 6° 

0,0 

-40 -20 0 20 40 

angle (°)

• Tapered laser bars coupled in a multimode fiber (100 µm) 

coupled power = 10 W at 21A, 13°C 

24 

20 

With a new beam shaping technique 

Coupling efficiency 

60 

50 

Optical power (W) 

16 

12 

8 

4 

0 

Emitted power 

Coupled power 

0 

0 5 10 15 20 25 30 35 

Current (A) 

40 

30 

20 

10 

Coupling efficiency (%)

• Tapered laser bars coupled in a multimode fiber 

coupled power = 10 W at 21A, 13°C with a new beam 

shaping technique : method 

Requirement on beam product parameter 

• Beam product parameter of a beam: 

BPP = (width) x (divergence) 

if non symetric, BPP x and BPP y 

• Regulation for an efficient optical coupling: 

BPP source < BPP fibre (100µm, NA=0.26) 

• Laser diode bar BPP: 

BPP // ~ (100-1000)xBPP ⊥ 

reshaping of the beam prior to fibre coupling 

beam 

fibre

Beam shaping technique 

General principle of “Optical stacking” 

1st plate 

2nd plate 

Input 

“Flat”Beam 

N intermediary 

beams 

Output 

“Stacked” 

Beams 

Fibre 

BPP // =X // x θ // 

BPP ⊥ =X ⊥ x θ ⊥ 

squared BPP ⇒ BPP // / N = BPP ⊥ x N

θ ⊥ 


Plates arrangement 

2nd plate 

Input beam: 

//: 2.6mm x 7° 

⊥: 0.5mm x 0.7° 

Number of sub-beams: 7 

Output beam: 

// : 0.37mm x 7° = 2.6 mm° 

⊥: 3.5mm x 0.7° = 2.45 mm° 

1st plate 

θ // 

Patent : C. Larat et al, Patent WO0014836.


Schematic optical system 

Laser 

diode 

Collimating 

lens 

2 plates Focusing lenses Optical fibre

Optical module 

Focusing lens 

Cylindrical lens 

Plates 

SMA HP 

tput connector 

Collimating 

lens 

Mini bars 

Commercialized by Thales Laser Diodes

ars at 808-980 nm 

On the laser diode market, main firms: 

• 808-980 nm : 

•Thales Laser Diodes : bars emitting 30-40W, 

stacks emitting from 2 to 5 kW, 

•OSRAM : the same and tapered laser bars 

•Coherent 

• for others kinds od laser diodes : 

•High Power Laser, Alfalight, JDS Uniphase...

Fabrication 

•Materials 

• Epitaxy 

• Process 


Laser diodes 
















Results with broad-area lasers – FBH 

FBH 

Ferdinand-Braun-Institut 

für Höchstfrequenztechnik 

735nm GaAsP-QW / AlGaAs LOC Laser Structure: 

Typical Performance 

• Transparency current density j th 

< 200A/cm² 

• Threshold current for 100x1000µm² I th 

< 300mA 

• Gain coefficient Γ⋅G 0 

= 20cm -1 

• FA angle FWHM θ < 30° 

• Internal efficiency 0.8 

• Internal loss ≤ 1cm -1 

• T 0 

≈ 60K 

α - factor < 1.5 ⇒ good beam quality 

Comparable wall plug efficiency to longer wavelength structures 

Low temperature stability

Results with 732 nmbroad-area lasers – FBH 

FBH 

Ferdinand-Braun-Institut 

für Höchstfrequenztechnik 

1.0 

2.0 

2.0 

0.8 

• Threshold current Ith 1W/A 

• Conversion efficiency ≈ 50% 

• Reliability at facet load up to 20mW/µm 

Voltage U / V 

1.5 

1.0 

0.5 

η C 

P 

1.5 

1.0 

0.5 

opt. Power P /W 

0.6 

0.4 

0.2 

conversion efficiency η C 

0.0 

0.0 0.5 1.0 1.5 2.0 

Current I / A 

0.0 

0.0

Results with tapered lasers – FBH 

653365 - Diode 030302 

L = 2.75 mm; L RW 

= 1 mm; W RW 

= 3 µm; ϕ TR 

= 6° 

R f 

= 1%; R r 

= 94%; T = 25°C 

I th 

= 643 mA; S = 0.97 W/A; η C 

= 40% 

I = 5 A ⇒ P = 3.3 W 

P / W 

0.5 

1.0 

2.0 

3.0 

BW / µm FF / ° 

M 2 

∆x / µm Centr.lobe 

4.4 16.6 1.4 576 86% 

4.4 16.6 1.4 591 86% 

4.4 14.7 1.2 606 79% 

4.8 12.2 1.1 669 80% 

rel. Intensity / arb. units 

0.5 W 

1.0 W 

2.0 W 

3.0 W 

0 10 20 30 40 50 60 

Position x / µm

Results – FBH - Aging tests done with tapered lasers 

• Sample 653309 

• All five diodes show reliable 

operation over 3200 h. 

• The degradation rates were 

below 3.2x10 -5 h -1 (estimated 

lifetime > 6000 h). 

Laser 

020601 

020603 

M 2 

before 

Aging 

1.3 

1.5 

M2 after 

1007.4 h 

@ 1 W 

1.4 

4.3 

M 2 after 

3166 h 

@ 1 W 

1.2 

3.1 

Current I / mA 

2000 

1500 

1000 

020601 

020603 

500 

020705 

020713 

020716 

0 

0 500 1000 1500 2000 2500 3000 

Aging time t / h 

020705 

020713 

020716 

1.4 

1.3 

1.6 

2.0 

1.2 

1.7 

1.3 

1.3 

1.4 

Aging behaviour of 2 mm long 

devices at P = 1 W, T = 25°C

CeramOptec GmbH 

Medical applications : laser diodes at 732 nm Siemensstr. 44 

D-53121 Bonn 

Germany 

• 8W @ 732nm laser system 

– Applied for test of photo 

toxicity of photosensitizer 

• 10W @ 975nm laser system 

– Applied in dental 

applications 

• Cleaning of root canal 

• Cutting of soft tissue 

• 4W @ 732nm and 10W 975nm 

prototype laser system


Medical applications : laser diodes at 732 nm 

Coupling of 4W at 732nm from single emitters 

into an optical fibre with 400µm core and NA < 0.3 

• Bundle of 8 lasers (9 fibres) 

– ∅≈470µm, NA = 0.15 

– P ~ 11W 

• Coupling to application fibre 

– ∅ = 200µm, NA = 0.35 

– P ~ 8.4W 

• Outmatches originally planned 

specs significantly 

• Runs in “time- mode” = ON for pre- selected treatment time 

• Has been applied for test of photo- toxicity of photosensitizer


Application Test of 732 nm system I 

Evaluation of photo-toxicity of PDT substance (BLC2025) 

Typical test procedure 

• Growth of cell cultures 

• Incubation with photosensitizer in 

varying concentrations 

• Excitation of the sensitizer with 

different energy densities and 

total energy 

• Continuation of cell growth 

• Determination of survival rate, 

e.g. via concentration of 

enzymes, which only exist in 

living cells 

100µl cell suspension per well

Application Test of 732 nm system II 


• HT29 cell line, 732 nm, BLC2025, 30 minutes incubation 

• Variation of photosensitizer concentration 

120 

100 

80 

60 

40 

20 

0 

0µM 10µM 20µM 30µM 40µM 50µM 

concentration BLC2025 

10J/cm2 0.5 W 12 sec 10J/cm2 1 W 6 sec 20J/cm2 0.5 W 25 sec 

20J/cm2 1 W 12 sec 50J/cm2 0.5 W 70 sec 50J/cm2 1 W 35 sec


Application Test of 732 nm system III 

• 30 µM BLC 2025, 50 J/cm2, 35 J 

• Variation of Treatment time with constant energy 

120 

100 

80 

60 

40 

20 

0 

0.5 W 70 sec 1 W 35 sec 2 W 17 sec 3 W 12 sec 4 W 9 sec 5 W 7 sec 

laser setting 

PBS HEK293 BLC2025 HEK293 BLC2025 HT29


Application Test of 975 nm system 

Cutting of soft tissue 

• Comparable conditions of wounds 

– 8h after treatment with 100µm 

core fibre 

– 24h after treatment with 400µm 

core fibre 

• Higher power density leads to 

– more accurate cuts without 

carbonisation 

– Less postoperative pains 

– Slightly reduced treatment time

Application Test of 975 nm system 

Cleaning of root canal 


Advantages of smaller 

application fibre 

• Especially interesting 

in cases where a 

regular cleaning is not 

possible 

• Strong bended roots 

become accessible 

• Small space situations 

benefit from higher 

flexibility of fibre

At last : 

• Others laser diodes: 

-VCSELs (vertical emission), quantum cascade lasers ( 

intra-band recombination ), lasers with gratings (DFB, 

DBR) … 

- other wavelengthes 

- a lot of applications : Telecoms, dentistry, surgery, gas 

detection … 

• any questions

High Power Diode Lasers - Center for Biomedical Optics and New ...

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