Zhiyi WEI, H.HAN, P.Wang, J.Tian,

W.Ling, Z.Wang, J.Zhang

Nov. 23~25, 2005. Beijing

Phase control, synchronization and amplification of femtosecond Ti:sapphire laser

Institute of Physics, CAS, Beijing 100080, China

Sino-Germany Symposium on Quantum Engineering

Outline

Background and motivation

Phase control femtosecond laser

Synchronized femtosecond laser

Amplification of femtosecond laser

Summary and Acknowledgement

Background and motivation

Phase control femtosecond laser

Synchronized femtosecond laser

Amplification of femtosecond laser

Summary and Acknowledgement

Background

Laser- original from the optical quantum theory by Einstein. Laser- a kind of electric-magnetic wave. E(,t)=A(t/)cos (t+)

AA: Amplitude, Energy depend on fund: Amplitude, Energy depend on fund ccwavelength, 1nm was obtawavelength, 1nm was obtained with attosecond laser pulse.ined with attosecond laser pulse. controllable with femtosecond lasecontrollable with femtosecond laserr ，，pulse durationpulse duration

play a key role in laser development

Pursue the shortest pulse is a challenge work

Applications of Ultrashort Laser Pulse

Ultrashort laser

Attosecond Physics Ultrafast electronics, optical communication

High field physics, laser acceleration etc.,

Ultrafast phenomena

Femtosecond micro/nano fabrication

THz radiation

Frequency omb,Optical clock

UL——The key for seeking answer

Nobel Prizes

Pushing laser intensity

Pursue the highest laser intensity is another challenge work, the discover of Chirped Pulse Amplification lead to the revolutionary progress in power density.

I=E/E: energy : pulse duration: beam size

Ultrafast and Ultrastrong laser It is another challenge work to pursue high power laser.

Recent development of CPA laser

Facility Peak Power Type Pulse duration Pulse Energy

RAL,UK 1PW Nd:glass/OPCPA 600fs 600J

ILE,Japan 700TW Nd:glass/OPCPA 700fs 350J

JAERI,Japan 850TW Ti:sapphire 33fs 28J

MBI,Germany 100TW Ti:sapphire 50fs 5J

Phelix,Germany 1PW Ti:s/Nd:glass 500 fs 500 J

LLNL,USA 200TW Ti:sapphire 100fs 20J

LULI,France 100TW Nd:glass 300fs 30J

CEDEX,France 100TW Ti:sapphire 25fs 2.5J

QG-II,China 120TW Ti:sapphire 36fs 4.2J

SILEX-1, China 286TW Ti:sapphire 30fs 8.6J

Multi-100TW facilities are available in many labs in the world now.Some new facilities are under constructing

全世界最高聚焦功率密度激光

The record works on TW laser

The highest peak power—850W JAERI, Japan, K.Yamakawa et al, The highest power density— 0.8X1022W/cm2 Michigan University, USA, S.Bahk et al, CLEO2004The highest peak power from OPCAP—100TW Russian, ALT05, Tianjin ChinaThe highest contrast ratio— 10-11

French, USA (Michigan PW) The shortest pulse duration— 1TW/10fs,10TW/12fs AIST Japan, H.Takada et al

Motivation of this talk

laser1

laser2 Laser N

1. Limitation Because of the limited crystal size and optical damage threshold, it has a Bottle Neck effect on the increasing of laser peak power.2. A new way toward higher intensity Phase controlled and synchronized n femtosecond ultra-strong lasers, it will enable us to generate an un-precedent power density of n2I.

Phase Controlled5-fs, 100 MHz

Ti:Sapphire Laser

Highly Energy Stable Multi-pass Amplifier

30 fs

Pulse Stretcher(negative Chirp)

Material Compression

10 kHz, 1 mJ30 fs

Phase Control+

Puls Selector

Hollow Fiber Comp.

10 kHz, 0.5 mJ, 5 fsPhase Controlled

A. Baltuska, et al., Nature, 421, 611 (2003)

Diagram show on CEP controlled CPA

Pow er am plifier

gas target

H igh-pass filter

Vacuum

Q uasi-m onocycle“cos” driver laser fie ld

Bandpass m irror

Isolated attosecond XUV pulse

cw pum plaser

Detector of fastCEP drift

Detector of slowCEP drift

AO M

Phase-lockingelectronics

Pum p laser

Ti:Sa oscillator Stretcher Com pressor

-15 -10 -5 0 5 10-1

0

1

-20 -10 0 10 20

0

8

A(t) =/2=0

Ele

ctri

c fi

eld

str

eng

th (

a.u

.)

Time (fs)

Inte

nsi

ty

Delay (fs)

1.5 2.00

1

Photon energy (eV)

Inte

nsi

ty

1000 800 600

Wavelength (nm)

Output of a 0.1-TW CEP-stabilized

Ti:sapphire system in Vienna

Laser for attosecond generation

Background and motivation

Phase control femtosecond laser

Synchronized femtosecond laser

Amplification of femtosecond laser

Summary and Acknowledgement

Outline

Stable femtosecond Ti:sapphire oscillator

Stability <1%Average power >1WPulse duration 15 ～ 30fsPeak Power ~1MWTunable range 760nm~850nmRepetition rate 50 ～ 100MHz

600mm

200mm

Pulse duration and stability

-40 -20 0 20 400

1

2

3

4

5

6

7

8

Ultralasers

Inte

nsity

Time delay (fs)0 2 4 6 8 10 12

0.0

0.2

0.4

0.6

0.8

1.0

1.2

Average power of fs Ti:sapphire laser

Powe

r(a.u

)

Running Time (hour)

<20fs

2.3 fs

Progress on Ultrashort Laser Pulses

Toward Monocycles pulse (<3fs in visible range )

L.Xu et al., Opt Lett, 21, 2008 (1996)

Carrier-envelope phase (CEP)

Principle of carrier envelop phase control

Carrier-envelope -phase (CEP)

Carrier-envelope offset frequency fceo

f =nf

rep

2(nfrep

nfrep

nfrep

f=2(nfrep nfrep

Self-reference technique

Stabilizing laser cavity length for locking frep

Modulating pump power for locking

Layout of experiment for CEP controlantenna

TV-Rb clcok10MHz

PLL

for frep

PLL

for CE

P

PCF

Grating

Beat frequency

0 50 100 150 200 250 300 3500

10

20

30

40

50

60

70

80

90

Locking

RF

fr

eq

ue

ncy(M

Hz)

Time(s)

Without Locking

fceo

frep

0 50 100 150 200 250 300 350

6

8

10

12

14

16

18

20

RF

fr

eque

ncy(

MH

z)

Time(s)

Without locking

Locking

Locking of CE phase with TV－ Rb clock

f2=+nfrep f1=+mfrep

frep frep

f

I (f)

fDFG= (m-n)frep DFG: 627-1000nm1680nm()

Free CE phase, f1 = nfrep

SHG: 1680nm 840nm(2)

CEP locked, f2 = 2nfrep

DFG: Difference frequency generation: fDFG= f1 -f2= (+mfrep)-(+nfrep)= (m-n)frep

Stabilized CE phase with DFG technique

DFG of the ultra-broaden band laser spectrum will generate a self-stabilized femtosecond frequency comb at wavelength around 1.5micrometer, it will be free of the electronics control for frequency beat.M. Zimmermann et al., MPQ; T. Fuji et al., TUW; S. M. Foreman et al., JILA&MIT

OC T=10%

f=10 cm M1 M2

Ti:sa

M3

5W 532nmMillennia

600 700 800 900 1000 1100

10

100

1000

Inte

nsi

ty

wavelength(nm)

T=10%

The spectrum support pulse duration of less than 7fs

M1-M3: Chirped mirror

Cavity length 85 cm (F 170 MHz)

Ultra-broaden bandwidth fs laser

500 600 700 800 900 1000 11000.0

0.2

0.4

0.6

0.8

1.0

Spe

ctra

l int

ensi

ty

wavelength /nm

532 nm 1064 nm

The latest result of spectrum

Directly output from the oscillator, covered from 550~1050nm

Outline

Background and motivation

Phase control femtosecond laser

Synchronized femtosecond laser

Amplification of femtosecond laser

Summary and Acknowledgement

Opt Lett, Vol.26,1806 (2001), Opt Lett, Vol.26,1806 (2001), Appl Phys B, Vol74.S171, (2002)Appl Phys B, Vol74.S171, (2002)

12

8

4

0

Inte

nsity

of

SF

G

543210Time (second)

S -P M illen n ia X s

S -P T -4 0 Z -1 0 6 C

P 1

R G

P 3

M 5

H R

P Z TP 2

P 4

M 1

P D

M 4

M 6

M 3M 2

T 1

C r:F

M 7 S E S A M

T 2

Ti:S

P D

To A C an d C C

P Z T D riv e r

F 2F 1

Ti:sapphire laser 600mW/18fs/820nm

Cr:forsterite laser

200mW/42fs/1300nm

For the first time the synchronization based on different gain media was demonstrated, the timing jitter is less than 1fs.

First synchronization between two different femtosecond lasers

Robust synchronization based on the improved design

Average power:>1W Pulse duration: 30 ～ 70fs Tunable range: 730 ～ 850nm Timing jitter: <400a Unstability: <1 ％ Tolerance of mismatch of cavity length: >10mm

Measurement of SFG and timing jitter

0.0 0.5 1.0 1.5 2.00.0

0.1

0.2

0.3

0.4

0.5

0.6

0.0 0.5 1.0 1.5 2.00.48

0.49

0.50

0.51

0.52

Inte

nsity

(a.

u.)

Time (s)

Nor

mal

ized

inte

nsity

Time (s)

V ＝ 0.5Vstandard ＝ 0.00653 t

I(t)

K

Timing jitter

V/V

SFG

j

V

VK

~

The cross-correlation trace (SFG) and its fluctuation at half amplitude. The fluctuation is proportional to timing jitter and was measured within 5s, it shows the timing jitter is less than 400as.

J.Tian et al; Opt Lett., Vol.30, 2161(2005)

Measurement of CEP between two lasers

0 20 40 60 80 100 120

-70

-60

-50

-40

-30

-20

-10

0

frep

frep+

Beat frequencyCentral frequency: 78.75 MHzSpan: 150 MHzResolution:100 KHzSweep time: 50 ms

inte

nsit

y (d

Bm

)

frequency (MHz)

frep-

frep ： Repetition rate,

90MHz ： ~28MHzS/N ： 41dB

f1=1+nfrep

f2=2+nfrep

f1- f2 1- 2

1 2

frep frep

f2=2+mfrep f1=1+nfrep

f

I (f)

frep

1

2

Considering the coupling inside the medium, each laser will suffer the frequency shift. For laser 2:

)exp(8 2

12

122 ddST

LPn

]})(exp[]{exp[4 22

12

122 ddST

LPn

Induced frequency shift

laser1

laser2

Coupling area

Medium for XPM

Where: P1 ： Intra-cavity peak power of laser 1

2 ： The central wavelength of laser 2

S ： The interaction area L ： The effective interaction length T1 ： Pulse of pulse duration

= 2c(1-2)/(T102)

The walk off parameter

for Vg1 = Vg2

for Vg1 Vg2

-3 -2 -1 0 1 2 3 4 5 6 7-2.0

-1.5

-1.0

-0.5

0.0

0.5

1.0

1.5

2.0

Ind

uce

d f

req

uen

cy s

hif

t Initial normalized time delay

Vg1 箎 Vg2

Vg1=Vg2

Induced-frequency shift as the function of the normalized initial delay of both the lasers

dd

T

GVDP

T

GVDP

S

LnT

21

12

12

2128

Build up time of synchronization

So the time to reach synchronization is:

/]1)1[( NdNT

fT d

offT

1

β1log0 1000 2000 3000 4000 5000 6000 7000 8000 9000 10000

-4-3-2-10123456

wav

elen

gth

shift

(nm

)Round trip times

wavelength shift of front laser wavelength shift of hind laser

0 1000 2000 3000 4000 5000 6000 7000 8000 9000 100000.00

0.05

0.10

0.15

0.20

0.25

0.30

Nor

mal

ized

del

ay

delay between both pulses

From the frequency shift, it is possible to deduce the relative time delay between two closer pulses:

Here <0, after N times round trip inside cavity, the new delay time will be:

The time interval and accumulated wavelength shift of both lasers versus round trip times cross in the crystal.

12

12

22

2

12

21

21

1

2

2

r

GVDGVD

T

c

r

GVDGVD

T

c

And wavelengths shift is

Actively synchronization between picosecond and femtosecond lasers

ps laser ： central wavelength 1064nm ； 7ps ； output >1W 。 fs laser ： central wavelength 810nm ； ~50fs ； output >600mW

ps laser

cavity controller

fslaser

86MHz

816MHzPLL

BBO

PLL

Adjustable delay

DetectorSFG

Before synchronization

Aftersynchronization

1064nm 810nm 532nm 460nm 405nm

Sum frequency generation between fs and ps laser

445 450 455 460 465 470 475 4800

500

1000

1500

2000

2500

3000

3500

4000

理 论 曲 线 实 测 曲 线

(a.u.)

强度

( nm)波 长

Spectrum of SFG laser

Theory: 7.1nm

Experiment: 5.5nm

Outline

Background and motivation

Phase control femtosecond laser

Synchronized femtosecond laser

Amplification of femtosecond laser

Summary and Acknowledgement

Development of TW laser at IoP Beijing

Extreme Light I (in 1999 ） Pulse energy ： 36mJ Pulse duration ： 25fs Peak power ： 1.4TW

Extreme Light II （ in 2001 ） Pulse energy ： 640mJ Pulse duration ： 31fs Peak power ： ~20TW

New design and system of 20TW peak power with two modes

Pro-350-101.4J/532nm/10Hz

AOPDF

Vacuum compressor

Evolu

tion 20

527nm

/1kH

z

1 kH

z pre-

amp

lifier

Main amplifier

Verdi-10 1W/fs oscillatorÖffern stretcher

Pro-350-101.4J/532nm/10Hz

Space2×4.5m

Two output with two repetition rate2mJ/990Hz; 20TW/10Hz

Construction of multi-100TW laser system

500 mJ/ 532nm/10HzSingle frequency laser

CEP controlled oscillator20fs/5nJ/80MHz

OPCPA, 2mJ/10 Hz

Finial main amplifier15 J, 1Hz（ or single shot)

Second main amplifier~1J, 1Hz

comprerssor8J/40fs/200TW

3J /532nm/1Hz or800mJ/532nm/10Hz

~50J/ 527nm pump laserSingle shot (~20min) 1Hz

Strtetcher>600ps

Adaptive optical system1×1021

1nJ

2106

14/3J

160

40

500MW/cm27/0.8J

14/7

50

Jp ＝ 2J/cm2

Jp ＝ 2J/cm2

200mJ/cm2

50J/527nm pump laser

Am

plifier II

Am

plifier IOffern Strectcher

1.5J/532nm/10H

z

CW

532

nmpu

mp

lase

r

fs o

scill

ator

500m

W/ 2

0fs

8J/40fs/800nm

～200T

W

Target Chamber II

Pre-pulseGenerator

600mJ/30fs/

~20TW

/800nm

Target Chamber I

Final amplifier~15J/800nm/20min

1mArea for power supply, 1X6 meters Control Platform

Door

Clear door

Room size:14X8 meters

Compressor I

40J/527nmPump laser

1.5J/532nm/10H

z

500m

J/10

Hz

532n

m S

F L

aser

Compressor II

Arrangement of lab for multi-100TW laser

Layout of 50J pump laser

～ 0.2 米

～ 2.6 米

MP1 晶体 85×20mm

IR5

IR4

IR3

IR2

MP2

MP3

MP4

MP5MP6

MP7

MP9

MP10

M2

M3

M4

M5

M6M7

M8

M9

M10

M11

M12

～ 2.0 米～ 2.16 米

～ 2.16 米

～ 0.5 米～ 0.6 米

～ 0.7 米

～ 0.3 9 米

0.1 1

～ 0.2 7 米

PC

箎箎 箎

Design of main amplifier

～ 20

1650

A

10

1650

B

Artificial Ti:S crystal shape for eliminating ASE

Ti:sapphire: Dia 85mmPatent design

Space size of the chamber ： 900×700mm,Incident angle: 24 degree ， diffractive angle: 51degree

Vacuum pumps

Layout of vacuum compressor

-150-120 -90 -60 -30 0 30 60 90 120 150

0.0

0.2

0.4

0.6

0.8

1.0(a)

compressed pulse seed pulse

Inte

nsi

ty(a

.u)

duration(fs)-150 -120 -90 -60 -30 0 30 60 90 120 150

1E-5

1E-4

1E-3

0.01

0.1

1

(b) compressed pulse seed pulse

Inte

nsi

ty(a

.u)

duration(fs)

Same grating groove between stretcher and compressor

(1200/mm)

-150 -120 -90 -60 -30 0 30 60 90 120 150

0.0

0.2

0.4

0.6

0.8

1.0(a)

compressed pulse seed pulse

Inte

nsi

ty(a

.u)

duration(fs)

-150 -120 -90 -60 -30 0 30 60 90 120 1501E-8

1E-7

1E-6

1E-5

1E-4

1E-3

0.01

0.1

1

10

(b) compressed pulse

seed pulse

Inte

nsi

ty(a

.u)

duration(fs)

Calculation of the optimized parameters in compressor

Different grating groove between

stretcher and compressor (1480/mm)

Large grating from JY

Holder for gratings

Summary

A multi-beams CPA laser with CEP control and synchronization was proposed, it will be enable us to obtain n2 times intensity by coherent overlap the laser beams at target. We locked the CE phase of fs oscillator, ultra-broaden bandwidth was realized with chirped mirrors technique, it will be enable us to further lock CE phase with DFG.Robust synchronized femtosecond lasers with timing jitter of sub-400as was demonstrated, tolerance of cavity length mismatch is longer than 10m.New technique for eliminate ASE from large crystal was proposed.

ACKNOWLEDGEMENT

Thanks to Mr.Zhu Jiangfeng( 朱江峰 ) 、 Gao Cunxiao ( 高存孝 ) 、 Zhao Linghui( 赵玲慧 ),Zhao Huan( 赵环 ) 、 Zhang Wei( 张炜 ) 、 Zhao Yanying （赵研英） ,Tong Juanjuan （佟娟娟） and Wang Yanghui （王延辉） for their partly works.Collaboration and technical discussion with Prof W.Zhao （赵卫）， Prof.J.Pan （潘建伟） and T.Yang （杨涛）Supports by Prof Nie Yuxin （聂玉昕） , Prof Sheng Naicheng （沈乃澄） and Mr Li Dehua( 李德华 ).

Funds supported by NSFC and Chinese Academy of Sciences are appreciated

Thank You for your attention!