Folienvorlagen für Seminarvortrag

Novel laser concepts

HR-mirror out coupling mirror

disccooling

diode laser

focusing optic

diode laser

focusing optic

fiber

HR-Spiegel

diode laser

focusing optic

Slab

HR-mirror

y

zDisc laser

Slab laser

Fiber laserlaser beam

inner cladding

outer cladding

active corepump

light

laser radiation

refractive index profile

n

ri

meridional rays helical rays

Double-clad fiber laser

0 5 10 15 20 250

20

40

60

80 D-shape

rectangular

dec. core

circular

abso

rptio

n [%

]

fiber length [m]

Improving pump absorption by pump core design

Improving the pump-absorption by mode mixing

kidney shaping

Double clad fiber laser (today)

1994 1996 1998 2000 2002 2004 2006 2008 20100

200

400

600

800

1000

1200

1400

1 kW

single mode multi mode

260 W

135 W

200 W

400 W

150 W 170 W

?

600 W

485 W

110 W

9,2 W5 W 30 W

272 W

ou

tpu

t p

ow

er [

W]

year

M2~ 1

600 W

most recent result … cw fiber laser: P= 1.3 kW M2< 3 @ MFD 25 µm (accepted @ CLEO postdeadline)

- immunity against thermal problems

- high gain - low threshold - high efficiency

- low intrinsic loss - large interaction length - exploitation of weak transitions

- large bandwidth - tuneability - short pulse generation + amplification

- STRONG NONLINEARITY

Properties of fiber lasers

Low-NA large-mode-area fiber design

core <10 µm core NA = 0.1 – 0.2

absorption length > 20 m

n

n

active core pump core

coating

double-clad single-mode fiber

double-clad large-mode-area fiber

active core pump core

coating

core = 30 .. 40 µm core NA = 0.06 .. 0.08

absorption length < 10 m

increased mode-field diameterreduced fiber length reduced nonlinearity

fiber stretcher300 m, MFD = 6.6 µm

Isolator

Isolator

diode laser

Transmission grating compressor

Output

fs-oscillator single-modepreamplifier

diode laser

Yb-dopedpower amplifier

CPA-fiber amplifier – high average power system

1060 nm,150 mW,

150 fs, 75 MHz = 22 nm, = 250 ps

@ 15 mW = 20 nm, = 225 ps

@ 2 W

CPA-fiber amplifier – power amplifier

Yb-dopedpower amplifier

diode laser976 nm

Yb-doped large-mode-area fiber

length: 13.5 mcore: = 28.5 µm, NA = 0.06, MFD = 23 µminner clad.: = 400 µm, NA = 0.38, Ddoping: 700 ppm (mol) Yb2O3

0 20 40 60 80 100 120 140 160 1800

20

40

60

80

100

120

140 Slope efficiency ~80%

Ou

tpu

t p

ow

er [

W]

Launched pump power [W]

beam quality:diffraction-limited (M2 = 1.1)

degree of polarization: ~ 50% (3 to 1)

output characteristics

CPA-fiber amplifier – power amplifier

Yb-dopedpower amplifier

diode laser976 nm

1020 1040 1060 1080 11000.0

0.2

0.4

0.6

0.8

1.0

= 20.1 nm

Inte

nsi

ty [

a.u

.]

Wavelength [nm]

-1.0 -0.5 0.0 0.5 1.00.0

0.2

0.4

0.6

0.8

1.0

= 224 ps

Inte

nsi

ty [

a.u

.]

Time [ns]

Yb-doped large-mode-area fiber

core: = 28.5 µm, NA = 0.06doping: 700 ppm (mol) Yb2O3

inner clad.: = 400 µm, NA = 0.38, Dlength: 13.5 m

emitted spectrum at 140 W pulse duration at 140 W

Air-clad large-mode-area microstructure fibers

high numerical aperture inner claddingradiation not in contact with coating materials

Yb:KGWoscillator

grating stretcher

preamplifier

diode laser

diode laser

AOM I AOM II

grating compressor

FR

diode laser

Yb

-do

ped

po

wer am

plifier

to application

preamplifier

PBS

Inner cladding: = 150 µm NA > 0.55Core: = 28 µm, NA = 0.05, MFD ~25 µmPump light absorption: 9.6 dB/m @ 976 nm

High energy fiber CPA system

250 fs 1 W

750 ps

1 W~10 kHz to ~MHz