Semiconductor lasers: What's next?

Grigorii Sokolovskii

Ioffe Institute, St Petersburg, Russia

gs@mail.ioffe.ru

Outline• Applications of semiconductor lasers. ‘Revolution’ of light.

• Basic principles of laser operation (only to remind).

• Absorption and gain in semiconductors, inversion of population and conditions for it's achievement.

• Rate equations. Lasing threshold. Laser efficiency.

• Modulation of the laser signal. Gain clamping.

• Fiber-optical applications. DFB and DBR lasers. VCSELs and VECSELS

• Waveguide in LD structure. Modes of the waveguide.

• Beam-propagation (‘beam-quality’) parameter M2 and how to measure it. Achieving maximum power density with LDs.

• Interference focusing of LD beams.

• What’s next? New applications and problems to solve.

Applications of LDs

• Telecoms• Data reading/recording• Laser printing• Pumping of the solid-state and fiber lasers • ‘Direct’ applications: cutting/drilling/welding • Biology and medicine

$7B → $1T

Applications of LDs

• Telecoms• Data reading/recording• Laser printing• Pumping of the solid state and fiber lasers• ‘Direct’ applications: drilling/cutting etc• Biomedicine

1. Surface and edge-emitting(e.g. VCSELs, VECSELs, GCSELs, etc and ‘striped’ LDs)

2. Broad and narrow area Broad: high power, poor beam quality;Narrow: low power, better beam quality

Types of LDs

LDs for Mid-IR (1600-5000 nm)

0

10

20

30

40

50

60

70

80

1300 1500 1700 1900 2100 2300 2500 2700

Wavelength, nm

Sp

ectr

al d

ensi

ty

W

/nm

LED22

LED20f=500 Hz

LED18

In Mid Infrared spectral range 1600-5000 nm lies strong absorption bands of such

important gases and liquids as:

CH4 , H2O, CO2, CO, C2H2, C2H4, C2H6,

CH3Cl, OCS, HCl, HOCl, HBr, H2S, HCN, NH3 , NO2 , SO2 , glucose and

many others.

Optical tweezers

Waveguide: light in matter

‘Inverse’ waveguide: matter in light – optical tweezers

Laser projectors

Microvision SHOWWX Laser Pico Projector

MacWorld 2010 Best of Show award

Samsung H03 Pico Pocket Sized LED Projector

Aiptek PocketCinema T30

Basic principles of laser operation

Gain + Feedback

0( ) xS x S e

Basic principles of laser operation

Lasing threshold

0( ) xS x S e 2 20 0(2 ) LS L R S e S

1lnout R

L threshold out in

Spontaneous and stimulated emission

E1

E2

E1

E2

Spontaneous Stimulated Absorption

dSAn

dt dS

BSndt

dSBSn

dt

Basic principles of laser operation

‘Negative’ temperature

2

1

E

kTn

en

Gain: inversion of population

Basic principles of laser operation

E1

E2

T

n

3- & 4-level systems

E1

E2

E3

E1

E2

E3

E4

Laser diodes: Some basics

Vibronic laser

E1

E2

E3

E4

Ev

Ec

Eg

Diode laser

Ec – conduction bandEv – valence bandEg – energy gap

QWs and QDs are the ‘artificial atoms’ :)

Laser diodes: Some basics

ElectronsElectrons

Photon

CurrentCurrentCurrentCurrent

Quantum Dot or Quantum Well

Conduction band

Valence bandValence band HolesHoles CurrentCurrentCurrentCurrent

NN--typetype PP--typetypeNN--typetype PP--typetype

Light generation and absorption in semiconductors

‘Golden’ rule of Quantum mechanics: 22

fW f H i

2( ) (1 )absorbtion v cW B M S E f f

2( 1) ( )(1 )radiation v cW B M S E f f

Absorption probability:

Radiation probability:

2 2( ) (1 ) ( )( )radiation absorption c v c vW W W B M E f f SB M E f f

( ) ( ) ( )sp stW E r E Sr E 2

( ) ( ) (1 )sp c vr E B M E f f 2

( ) ( )( )st c vr E B M E f f

The total radiation probability:

Light generation and absorption in semiconductors

What is the condition for stimulated emission?

c v c v gF F E E E

1 10 0

1 exp 1 expc v

c c v v

f fE F E F

kT kT

( ) 0str E 2

( ) ( )( ) 0st c vr E B M E f f

Inversion of population:

c v gF F E

Inversion of population

http://britneyspears.ac/physics/fplasers/fplasers.htm

gvc EFF

Forward-biased p-n-junction is both the source for the inversion of population and for the name of the “laser diodes”

Stimulated and spontaneous emission rate: 3D

ћω=E

r

rst

rsp

fce

fvh

ρ(E)

-ρ(E)

T↑

Eg

)1()(~)( vcsp ffEEr

))((~)( vcst ffEEr

kTFE

fcc

c

exp1

1

kTFE

fvv

v

exp1

1

gEEE ~)(

Density of states: Low-Dimensional vs 3D

Bulk semiconductor

Quantum Well

Quantum Wire

Quantum Dot

32

3 2 2

2( )

2D g

d mE E E

2 02( ) ( )D QW

mE n h E E

12

1 20

2 1( )

2QWW

D

n mE

E E

0 0( ) 2 ( )D QDE n E E

Evolution of the threshold current density: from 3D to Low-Dimensional

Density of states: Low-Dimensional vs 3D

Bulk semiconductor

~1 kA/cm2

Quantum Well

~100 A/cm2

Quantum Wire???

Quantum Dot

~10 A/cm2

3D

E

rst

0( ) 2 ( )QD QDE n E E

QDs vs 3D

Lower threshold

Lower temperature dependence of the laser parameters

But: at low QD density threshold may NOT be reached

Narrow spectrum for IDENTICAL QDs

But: broad spectrum for inhomogeneously broadened QDs

QD

k0nf

kz

kx

nc

ns

nf fkxf

kxf

φc

φs

220

22fzx nkkk mfk csx 22

mm

xfm

z Nkknkk 0)(22

0)(

fmcs nNnn ,

Laser diodes: The waveguide

Eg ↓ ↔ n↑

.

.

x

k0nf

z

k0ns k0nc

x

k0nf

z

k0ns k0nc

Modes of the waveguide

.

.

Composing Rate Equations

The simplest model

red

J

J is the average pump current densityn is the average carrier concentration in the active regionS is the average photon concentration (average intensity)

Carriers, steady-state:

Pump rate = Recombination rate

Carriers, time-dependent:

red

J

dt

dn

SngN

cn

ed

J

dt

dn

effs

)(

stsp Srred

J

dt

dn

Bn

nBnr s

ssp

1,2

gainrst ~ )(ng

N

cr

effst

Composing Rate Equations

rS

p

Photons, steady-state:

Total radiation probability = Recombination rate

Photons, time-dependent:

p

Sr

dt

dS

pstsp

SSrr

dt

dS

pseff

SnSng

N

c

dt

dS

)(

SnnAn

ed

J

dt

dn

SnSnnA

dt

dS

ts

pst

Г - confinement factorβ - spontaneous emission factornt - transparency concentrationA - linear gain coefficientτs - spontaneous recomb. timeτp - photon lifetime

Lifetimes

Bns

1

Spontaneous: Photon lifetime:

p

S

dt

dS

τs ~ 1 ns if n ~ nt, then: p

t

eSS

0

c

LNt eff

r

2 22

0

2

0)( ReSeStS inp

eff

Lc

LN

r

RLN

cin

effp

1ln

11 τp ~ 1 ps

L ↑ → τp ↑αin ↑ → τp ↓R ↑ → τp ↑

Rate Equations for QD LD

Ws

WE

E

WW

E

EW nf

nf

n

ed

J

t

n

''0

Es

EE

G

GGE

EW

E

EEE

WE nf

nf

nf

nf

n

t

n

''''00

Gs

GE

G

GtrGGG

EG nf

nSnnAf

n

t

n

')('0

p

p

Gs

GtrG

SnSnnA

t

S

)(

GS

ES

τWG

τWE

τE

τG

…where f is the filling factor

5ML InAs

Steady-state solution of the Rate Eqs

0

0

SnnAn

ed

J

dt

dn

SnSnnA

dt

dS

ts

pst

st

spt

n

ed

JSnnA

nSSnnA

0

sspt

sp

n

ed

Jn

ed

JnnA

n

ed

JS

pt

s

Ann

ed

Jn

1

pt

s

p

An

edJ

edS

S

1

0

Steady-state solution of the Rate Eqs

pt

s

Ann

ed

Jn

1

pt

s

p

An

edJ

edS

S

1

0J

J

S

Jth

n

Jth

nth

β↑

β↑nt

ptth A

nn

1

thsp

ts

th ned

An

edJ

1

Lasing Threshold

0 0.2 0.4 0.6 0.8 1

5

10

Thickness, f

Thr

esho

ld, J

thsp

ts

th ned

An

edJ

1

RLN

cin

effp

1ln

11

0 5 103 0.01 0.015

1

2

3

4

5

Inverse Length, 1/L

Thr

esho

ld, J

R↑R↑

0 200 400 600 800

1

2

3

4

5

Length, L

Thr

esho

ld, J

R↑

Lasing Threshold

Threshold vs Temperature

100 200 3000

1

2

Temperature, T

Thr

esho

ld, J

100 200 3000.1

1

10

Temperature, T

Thr

esho

ld, J

0

expT

JT

)(0 TfT

Laser efficiency

thp

ii JJed

SJJ

~~

electrons

photons

J

J

i

total

active

~ Pumping efficiency

Internal quantum efficiency

32

2

CnBnAn

Bni

Ev

Ec

Ev

Ec Ev

Ec

Evv

free-carriers Auger

Laser efficiency

thp

i JJed

S

~ RL

V

N

cSP

eff

1ln

1

2

121

thp

ieff

JJedRL

V

N

cP

~1

ln1

2

121

RLN

cin

effp

1ln

11

d

VJJWLI

th

in

i II

RL

RLe

P

1

ln1

1ln

1~

2

121

outin

outi

in

i

th

d

RL

RL

IIe

P

~

2

11

ln1

1ln

1~

2

121

differential efficiency:

R↑

I

P

Ith

ηd

Laser efficiency

serial

thd

serial Ire

I

IIe

Ire

I

P

21

21

R

Lin

id1

ln1~

21

Measuring IQE:

L

1/ηd

i~2

Riin1ln~2

Lasing efficiency:

I

P

Ith

U

rserial↑

I

P

Ith

η(1/2)

rserial↑

Turn-on delay

t

J

Jth

t

S

t

S

Δt

SnnAn

ed

J

dt

dn

SnSnnA

dt

dS

ts

pst

s

ts e

ed

Jtn

1)(

thntn )(

J

J

JJ

Jt th

sth

s

ln

?

Turn-on delay

J

J

JJ

Jt th

sth

s

ln

If J = 2Jth, τs = 1 ns: Δt = 0.7 ns t

J

Jth

Non-return-to-zero (NRZ) modulation

t

S

Δt

t

J

Jth

t

S

RZ modulation

Turn-on delay of QD LDs

J

J

JJ

Jt th

sth

s

ln

J/Jth

Δt

Cτp

Non-QD laser diode:

pth

s CJ

Jt

QD LD:

SngN

cn

de

J

dt

dn

effs

)(

speff

nSSng

N

c

dt

dS

)(

)(),()(

)(),()(

)(),()(

00

00

00

tnJntnntn

tSStSStS

tJJtJJtJ

)( 00 nSgSgN

cn

de

Jn

effs

speff

nSnSgSg

N

cS

)( 00

Small-signal moduation

0)(

0)(

SngN

cn

ed

J

SnSng

N

c

effs

pseff

SngN

cn

de

J

dt

dn

effs

)(

speff

nSSng

N

c

dt

dS

)(

)exp()()(

)exp()()(

)exp()(

tibtS

tiatn

tijtJ

)( 00 nSgSg

N

cn

de

Jn

effs

speff

nSnSgSg

N

cS

)( 00

de

jbg

N

caSg

N

ci

effeffs

00

1

01

00

bg

N

ciaSg

N

c

effpseff

gN

cAAS

effs

,1

0 0

1g

N

c

effp

p

AS

02

0

Small-signal moduation

))(exp()()(22

0

20

Bp iB

de

j

ide

jb

de

jbg

N

caSg

N

ci

effeffs

00

1

01

00

bg

N

ciaSg

N

c

effpseff

222220

20

)()(

B )()(22

0

arctgB

Amplitude-freq. response of photons

gN

cAAS

effs

,1

0 0

1g

N

c

effp

p

AS

02

0

1

1/2

B(

)

I1

I2>I

1

222220

20

)()(

B

0

1AS

s

p

AS

02

0

Amplitude-freq. response of photons

-3

-2

-1

0

1

B(

)

)()(22

0

arctgB

0

1AS

s

p

AS

02

0

Phase-frequency response of photons

))(exp()()(22

0

AiAde

j

i

i

de

ja

de

jbg

N

caSg

N

ci

effeffs

00

1

01

00

bg

N

ciaSg

N

c

effpseff

222220 )(

)(

A2

)()(22

0

arctgA

Amplitude-freq. response of carriers

A(

)

222220 )(

)(

A

0

1AS

s

p

AS

02

0

Amplitude-freq. response of carriers

-3

-2

-1

0

1

A(

)

2)()(

220

arctgA

0

1AS

s

p

AS

02

0

Phase-frequency response of carriers

-3

-2

-1

0

1

2 B()

A()

B(

), A

()

π/2

π/2 shift in the phase-frequency responses means the energy flow between the photons and carriers (similar to the kinetic and potential energy in pendulum) which is called ‘relaxation oscillations’.

2)()(

220

arctgA

)()(22

0

arctgB

Phase-frequency response

0 0.5 1 1.5 2 2.5 3 3.5 40

1

2

3

4

5

6

время, нс

кон

цен

трац

ия,

о.е

.

n(t)

S(t)

Relaxation oscillations

NB: no relaxation oscillations in QD lasers!

Typical explanations: 1) QD LDs are too fast; 2) QD LDs are too slow

Eye-diagram

Eye-diagram

Gain clamping (gain saturation)

Laser diodes at extremely high pumping: pulsed vs CW

I

P

IthI

CW

pulsed

I

P

Ith

CW

pulsed

Gain clamping

ptr

tr

SNSSNNA

dt

dS

NSSNNA

ed

J

dt

dN

)1()(

)1()(

edNJ

S

S

A

edJJ

edS

ANN

S

S

ANN

thth

pth

p

ptrth

pth

,1

1,

1

1

22

th

pthth JJ

AedA

AJJ

AedNN

Quasi-analytical:

Asymptotical:

2 4 6 8 10 12 140

5

10

15

20

25

30

(I-Ith)/Ith

Concentration

.

N

ε=0

S

ε=0

pp

ASS 0

01

Gain clamping

SSngN

cn

de

J

dt

dn

effs

1)(

speff

nSSSng

N

c

dt

dS

1)(

J

S

Jth

0 5 10 15 20 25 30

20

10

0

10

20

частота, ГГц

откл

ик,

дБ

=0, =0

=21023

,

=21023

, =110-4

=0

pp

ASS 0

01

Gain clamping

Frequency, GHz

Res

pons

e,

dB

Application to the fiber optical communications

Application to the fiber optical communications

Double power: Double distance?

0

lg10P

PdB Typical attenuation: -20dB km

kmdB

dBL 100

/2.0

20

km

kmdB

dB

kmdB

dBPP

kmdB

PP

PL 115/2.0

3.0210

/2.0

2lglg10

/2.0

2lg10

)2( 00

kmPL 100)( if:

kmPL 200)100(

Wavelength / Time Division Multiplexing

Wavelength Selection

Gain Chip:

• 4mm length, 5µm wide waveguide

• 10 layers InAs QDs, grown on GaAs substrate

• waveguide angled at 5o

• facets AR coated: Rangled < 10-5

Rfront ~ 2 ·10-3

Distributed feedback (DFB) laser diodes

p-InP

n-InP

p-InP

n-InP

p-InP

n-InP

p-InP

p-InP

p-InP

n-InP

Distributed Bragg reflector (DBR) LDs

Diffraction grating in a waveguidex

k0nf

z

k0ns k0nc

mm

xfm

z Nkknkk 0)(22

0)(

x

z

k0Nm

Diffraction grating in a waveguide

N

Nkkz

20

x

z

k0Nm

x

z

k0Nm

1st order

2

k

zzz kkkk )1(

zzz kkkk 2)2(

2nd order

Distributed feedback/2

выход выход

Расстояние

Ам

пли

туда

022

2

Ez

E

n z n n z( ) cos( ) 1 02 ( ) cos( )z z 1 02

0 0 n c n c/ /

Р.Ф.Казаринов, Р.А.Сурис, ФТП, 1972, т.6(7), с. 1359-1365.H.Kogelnik, C.V.Shank, Journal of Appl. Phys, 1972, v.43(5), pp.2327-2335.

)2cos(42 022 zki

n c k n i 1 0 1 2

E z R z e S z ei z i z( ) ( ) ( ) 0 0

dR

dzi R ikS

dS

dzi S ik R *

202

2

0

0nc

Distributed feedback

202

2

00n

c

dR

dzi R ikS

dS

dzi S ik R * k n i 1 0 1 2

Vertical-cavity surface-emitting lasers VCSELs

(AlGa)Oxy

0 1000 2000 3000 4000 50000,0

0,2

0,4

0,6

0,8

1,0

Radial distance [nm]

Nor

mal

i zed

op

tica

l fie

ld in

tens

ity

Cu

rren

t de

nsit

y p

rofi

les

E2LP01

J

0 1 2 3 4 5 6 70.0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

ou

tpu

t p

ow

er [

mW

]

current [mA]

0.0

0.5

1.0

1.5

2.0

2.5

3.0

vo

ltag

e [V

]

SML InGaAs QD VCSELCW RT, single-modeaperture 3.5 m

960 964 968-80

-70

-60

-50

-40

-30 31

2

Vertical-extended-cavity surface-emitting lasers (VECSELs)

A.Mooradian, “High brightness cavity-controlled surface emitting GaInAs lasers operating at 980 nm”, Proceedings of the Optical Fiber Communications Conference, 17-22 March 2001

• Power• Beam quality• Spectral quality

LD ‘bar’

Problems of LDs

Broad-stripe LD

Power density &intensity gradient

Optical confinement

dxxE

dxxEf

2

0

2

)(

)(

Double confined

Separately confined

Modes of the waveguide.

.

x

k0nf

z

k0ns k0nc

x

k0nf

z

k0ns k0nc

mm

xfm

z Nkknkk 0)(22

0)(

Optical confinement

dxxE

dxxEf

2

0

2

)(

)(

2f

Managing mode structure with optical confinement

.

Higher power does not meanhigher power density… :(

Power density and LD power

‘Not impossible’ near-field distribution of the broad-stripe LD

Higher power: • Higher modes• Spots (filaments)• Astigmatism

Multi-moded and ‘spotted’ (filamented) radiation is difficult (and sometimes impossible) to focus!

Multimode LDs

Propagation of the Gaussian beam

exp(-r2/w2).

. .

Gaussian beams

Coordinate

Gaussian exp(-r2/w2) is the most dense distribution. Therefore, Gaussian beams are the beams of the highest ‘quality’.

Even the ‘ideal’ power density is limited due to the quantum mechanical uncertainty principle ΔpΔx=h

2

20

0 1)(

w

zwzw

2201)(

z

wzzR

NAw

0

exp(-r2/w2)

.

. .

2

00

wz

Beam waist size on the level of 1/e2 (86%)

Propagating beam size (beam diameter)

Wavefront curvature

Raleigh range (distance of √2-fold increase of diameter of the beam)

Gaussian beams

LD beams: From multi-mode to quasi-Gaussian

exp(-2r2/w2)

.. .

.

M2 – beam propagation parameter

Second moment properties

dxdyyxI

dxdyyxIxxx

),(

),(202

Definition of the second moment (or variance):

Leads to a universal, rigorous parabolic propagation rule:2

020

20

2 )()( zzz xx

which holds for any arbitrary real beam (Gaussian or non-Gaussian, spatially coherent or incoherent) in free space

• Can develop such a universial propagation rule only for the second-moment beam width definition

• Actually holds true for propagation through arbitrary paraxial optical systems as well

A.E.Siegman, How to (Maybe) Measure Laser Beam Quality, OSA Annual Meeting, 1998

Second-moment-based beam width definition

xxw 2

For a zero-mode Gaussian beam the standard deviation is related to the Gaussian spot size w by

Therefore for arbitrary real beams similar beam width definitions can be adopted:

These second-moment-based beam widths will propagate exactly quadratically with distance in free space. For any arbitrary beam (coherent or incoherent), one can then write using the second-moment width definition

A.E.Siegman, How to (Maybe) Measure Laser Beam Quality, OSA Annual Meeting, 1998

xxw 2

z

zwwM

)(02

20

2

,0

4,

2,0

2, )()( zz

wMwzw

yxyxyxyx

using this width definition,

Basic properties of the M2 parameter

M2 is a “times-diffraction-limited” parameter based on measured near and far field second-moment beam widths

M2=1 for a zero-mode Gaussian beams

Arbitrary real beam widths can then be fully described by six parameters:

A.E.Siegman, How to (Maybe) Measure Laser Beam Quality, OSA Annual Meeting, 1998

220000 ,,,,, yxyxyx MMzzww

Requires time-averaged intensity measurements only.NO phase or wavefront measurements!

0

2

w

wM measured

2

2

2

2

2 1)(

MM w

zMwzw

2

2

22

1)(zM

wzzR M

NA

Mw

M 2

2

2

22

2

M

wz M

M

2M

Quasi-Gaussian beams

Beam waist size on the level of 1/e2 (15%)

Propagating beam size

Wavefront curvature

Raleigh range

exp(-2r2/w2)

.. .

.

1000 500 0 500 10000

50

100

wM z 0.1 1( )

wM z 0.1 3( )

wM z 0.1 10( )

z

wM 0 0.1 10( )

wM 0 0.1 1( )10

Focusing of the quasi-Gaussian beams

exp(-2r2/w2)

.. .

.

How to measure M2 parameter?

follows:

1000 500 0 500 10000

50

100

wM z 0.1 1( )

wM z 0.1 3( )

wM z 0.1 10( )

z

wM 0 0.1 10( )

wM 0 0.1 1( )10

22

201

220

2

2

NAB

NAzB

NAzwAM

NA

Mw

M 2

2 with

Measurable: beam diameter as a function of propagation length:

221

2220

220

220

222 2)( 22 zBzBANAzNAzzNAzwzzNAwzwMM

4

2

21

22

2

10

2

BABM

BBz

BNA

How to measure M2 parameter?

M2 is different at fast and slow axis!

1000 500 0 500 10000

50

100

wM z 0.1 1( )

wM z 0.1 3( )

wM z 0.1 10( )

z

wM 0 0.1 10( )

wM 0 0.1 1( )10

Cylindrical lens No.1(Fast axis corrector)

Cylindrical lens No.1(Fast axis corrector)

Cylindrical lens No.2(Slow axis corrector)Cylindrical lens No.2(Slow axis corrector)

Measuring lensMeasuring lens

CCDCCD

How to measure M2 in your lab?

1. Use house-built setup with any CAL or CAD software(e.g. MicroCal Origin)

2. Use specialist hard- and soft-ware (e.g. DataRay)

Approx. time for one laser: 3 hrs (when you’ve got some experience)

Approx. time for one laser: 15 mins

Standard:ISO 11146

Measuring M2 parameter

0 1 2

0,5

1,0

1,5

10

20

30

40

50

60

Pow

er, W

Current, A

M 2 p

aram

eter

0 1 2

0,5

1,0

1,5

0

3

6

9

12

15

Pow

er, W

Current, A

M 2 p

aram

eter

Fast axis

Slow axis

M2 varies with current!

For broad-stripe laser diodes,M2 at slow axis is an order ofmagnitude higher comparingto that at slow axis…

M2 can be NOT measurable!

100 um high-power LD, 1.06 um

Don’t call it ‘Gaussian’ before you are sure…

Light emitting diode Lumiled, 0.63 um 350 mA, M2=500

Don’t overestimate the M2 parameter of the ‘nasty’ LD beams…

Narrow stripe LD, 1.06 um, 100 mA, M2=4

Interference focusing (Generation of Bessel beams)

Prism: interference of plane waves

Conical lens (axicon): interference of conical waves

J. Durnin // J. Opt. Soc. Am. 1987, A 4, P. 651-654B.Ya.Zel’dovich, N.F.Pilipetskii // Izvestia VUZov, Radiophysics, 1966, 9(1), P.95-101

vg

vg vg

vg cos2(x)

J02(x)

Bessel beams vs Gaussian beamsAxicon

Bessel beams are ideal for optical tweezers, micromanipulation and lab-on-a-chip applications

vgvg vg

Lense

distance

pow

er d

ensi

ty

distance

pow

er d

ensi

ty

Bessel beams are typically generated with vibronic lasers

VCSEL DO-701d, Innolume GmbH, axicon 1700, I=1 mА

G.S.Sokolovskii et al. // Tech Phys Lett, 2008, 34(24) 75-82

Main problem: Low coherence???

Interference focusing with Laser Diodes

Interference focuing with High-power Laser Diodes

Main problem: Poor beam quality

Radiation wavelength λ = 1.06 µm. Axicon apex angle 1700. Central lobe size d0 = 10 µm.

Multimode Filamented Oblique

Axicon apex angle 1700

Bessel beams from the broad-stripe LD

G.S.Sokolovskii et al. // Tech Phys Lett, 2010, 36(1) 22-30

Propagation length of Bessel beams generated from Laser Diodes

Распространение Бесселева пучка, созданного аксиконом

vg

vg vg

Фокусировка Гауссова и квази-Гауссова пучков линзой

exp(-2r2/w2)

.

. .

.

2M

NA

M

2

M2LD=10-50

M2LED=200-500

Распространение Бесселева пучка, сформированного

из расходящегося Гауссова пучка

zB0 J02(r) exp(-2r2/w2) z0 zB

.

vg

vg

.

Achieving ‘non-achievable’ intensity gradients with broad-stripe LDs

Broad-stripe LD 1.06 um, М2=22, interference focal spot dia = 4 um

LED 0.63 um, М2=200, interference focal spot dia = 6 um

(Fiber axicon(Fiber axicons manufactured by Maria Farsari and colleagues, FORTH)

Fiber axicons

5000100001500020000250003000035000

40

50

60

70

80

90

100

5000100001500020000250003000035000

40 60 80 10040

50

60

70

80

90

100

NA

M

2

1

Applications of LDsWhat’s next?

• Data reading/recording• Telecoms• Laser printing• ‘Direct’ applications: cutting/drilling/welding • Pumping of other lasers and frequency conversion • Biology and medicine

$7B → $1T

Laser projectors: Green Light?

Microvision SHOWWX Laser Pico Projector

MacWorld 2010 Best of Show award

Samsung H03 Pico Pocket Sized LED Projector

Aiptek PocketCinema T30

No need for focusing!

From laser printers to 3D printing

Telecoms/Datacoms: Silicon Photonics?

On-chip Datacoms: Size matters?Energy matters!

What counts? fJ/bit!

Polariton Laser?

Automotive applications: laser ignition?

Optical tweezers: lab-on-a-chip?

Waveguide: light in matter

‘Inverse’ waveguide: matter in light – optical tweezers

‘Lab’

‘Chip-in-a-lab’ ‘Lab-on-a-chip’

‘Lab-on-a-chip’

‘Laboratory’

Lab-on-a-chip

Fluorescent microscopy: need for color?

480 500 520 540 560 580 600 620 640 660

0,01

0,1

1

10

100

0,01

0,1

1

10

100

960 1000 1040 1080 1120 1160 1200 1240 1280 1320

Fundamental Wavelength, nm

Pu

mp

Po

wer

, mW

SH

Po

wer

, mW

SH Wavelength, nm

Extracellular heat shock proteins (Hsp70) and ceramides are known to possess high adjuvant activity for cancer vaccines and low-immunogenic vaccines against dangerous infections. Hsp70 and ceramide can activate receptors of the innate immunity (TLR4) and boost protective immune response reactions against abiotic stress factors and biopathogens.

Generation of Heat-Shock Proteins and Ceramides with Laser Diodes

Laser diode

Power supply

Hsp70 Pulse duration 100 nsFrequency 10 kHzWavelength 1060 nm

LDs for Mid-IR (1600 nm - 5000 nm)

0

10

20

30

40

50

60

70

80

1300 1500 1700 1900 2100 2300 2500 2700

Wavelength, nm

Sp

ectr

al d

ensi

ty

W

/nm

LED22

LED20f=500 Hz

LED18

In Mid Infrared spectral range 1600-5000 nm lies strong absorption bands of such

important gases and liquids as:

CH4 , H2O, CO2, CO, C2H2, C2H4, C2H6,

CH3Cl, OCS, HCl, HOCl, HBr, H2S, HCN, NH3 , NO2 , SO2 , glucose and

many others.

16 μm

Thank you for your attention!• Applications of semiconductor lasers. ‘Revolution’ of light.

• Basic principles of laser operation (only to remind).

• Absorption and gain in semiconductors, inversion of population and conditions for it's achievement.

• Rate equations. Lasing threshold. Laser efficiency.

• Modulation of the laser signal. Gain clamping.

• Fiber-optical applications. DFB and DBR lasers. VCSELs and VECSELS

• Waveguide in LD structure. Modes of the waveguide.

• Beam-propagation (‘beam-quality’) parameter M2 and how to measure it. Achieving maximum power density with LDs.

• Interference focusing of LD beams.

• What’s next? New applications and problems to solve.