Institute of Atomic and Molecular Science, IAMS, Taiwan, ROC

 

Wang-Yau Cheng, Chien-Ming Wu, Tz-Wei Liu and Yo-Huan Chen

Progressive report on portable Ti:sapphire comb laser

based on cesium-stabilized diode lasers

Chemistry laboratory

Hubble observatory

Keck observatory

Hard to incorporate VIS-UV comb laser into 。。。

Ti:sapphire laser most popular comb laser light source from NIR to UV

Difficulties for being conveyable

Conventionally, extending comb spectrum or 1f-2f interferometer is needed

Inconvenient pump laser

Mode frequency is actually not accurate enough and also sensitive to the environments

mfm

LOCKEDLOCKED

Self-reference

m~106 When~2 mHz instability fm~ 2 kHz instability

Directly referring and fm to narrow atomic two-photon transitions

mfmI(f)

f

F=4

6 P

6 SF=3

6 D

8S

822 nm

884 nm822 nm

884 nm

822 nm

884 nm

A project locking all comb laser parameters by cesium cells

Accuracy, comb-based CPT

Opt. lett. 32, 563 (2007)

Apply Physics B 92, 13-18 (2008)

submitted

-12

-11

(sec, log)

30 MHz

day

Bea

t not

e (k

Hz)

0 5 10 15 20

-2

-1

0

1

-1 0 1 2

-13

off lock

P+A

P

Allan deviation: 4*10-13

~150 Hz frequency uncertainty

822 nm optical frequency reference

Opt. lett. 32, 563 (2007)

To PMTCs cell

PZT17 cm

30 MHz

6S 8SF=3 F=3

Cs spectrometer

Extended-cavity diode laser Paper submitted

6S1/26D5/2;F=4~f’=6-2

6S1/26D5/2;F=3~f’=5-1

6S1/26D3/2;F=4~f’=2-5

6S1/26D3/2;F=3~f’=2-5

20 MHz

884 nm optical frequency reference

f

Difficulties: How to referring comb laser repetition rate directly to atomic spectrum

Population coherence between a and c states is thus built up

Cesium Ground state hyperfine splitting

a

b

c

Clock frequency

22

12

12

RR

RR cb

Coherent population trapping

Cesium Ground state hyperfine splitting

a

b

c

Clock frequency

CPT signal by comb laser is extremely sensitive to repetition rate

Repetition rate – 1/100clock frequency (mHz)

30-20-70-120 80 130 180 230 280 330 380

0.95

0.97

0.99

1.01

1.00

Flu

ores

cenc

e (A

rb. u

nit)

Repetition rate – 1/100clock frequency (mHz)

30-20-70-120 80 130 180 230 280 330 380

0.95

0.97

0.99

1.01

1.00

0.95

0.97

0.99

1.01

1.00

Flu

ores

cenc

e (A

rb. u

nit)

-80 -60 -40 -20 0 20 40 60 80

0.95

0.96

0.97

0.98

0.99

1.00

1.01

Flu

ores

cenc

e (A

rb. u

nit)

repetition rate 1/100 clock frequency (mHz)

52 mHz

-80 -60 -40 -20 0 20 40 60 80

0.95

0.96

0.97

0.98

0.99

1.00

1.01

Flu

ores

cenc

e (A

rb. u

nit)

repetition rate 1/100 clock frequency (mHz) repetition rate 1/100 clock frequency (mHz)

5.2 Hz

Summary

main marker from 884nm laser

scale: Cmob-CPT clock

Paper submitted

6S1/26D5/2;F=4~f’=6-2

6S1/26D5/2;F=3~f’=5-1

6S1/26D3/2;F=4~f’=2-5

6S1/26D3/2;F=3~f’=2-5

main marker from 822 nm laser

Opt. lett. 32, 563 (2007)

30 MHz

6S 8SF=3 F=3

30ms time constant

Cs spectrometer

1. no 1f-2f scheme

2. all comb parameters referring to atomic cesium transitions

On going works

170 mm

portable comb clock is now under construction

1. stable and small reference laser

3. small pump laser

2. small Ti:sapphire laser

criteria:

fiber laser + waveguide crystal

+

Optics letters 34, 1561 (2009)

10*30 mm

AOM2

Ti:S laser #1

Ti:S laser #2

532 nm Pump laser

Second harmonic

crystal

Color filter Interference

filter

C3

Molecule

Mirrors in UVAOM1

PZT

Signal

reference

Low noise detector (D1)

Low noise

detector (D2)

Multi-heterodyne comb laser spectroscopy (Collaborate with Dr. Yen-Chu Hsu’s group )

Reference:NIST, PRL 100, 013902 (2008)

With C3 molecules– UV comb references

Gergly

Cs MOT

Hand-size laser

宥寰

822 nm standard

子維comb laser建宏建明

宗翰

852 nm CPT芝佑

聖輝

彥龍

theory modeling

郁菁

建中 884 nm spectra

麗晶

It is a team work !Acknowledge the funding support from NSC, Taiwan

NSC94-2112-m-001-022-MY3

Cesium ground state

become mixed state

The wavefunction of mixed state will decay with a quantum beat (clock frequency)

When the phase of repetition rate matches the phase of this quantum beat, a stable mixed state or ground-state coherence will then be built up

Periodic-driven swing

first 10 kicks

0 20 40 60 80 100

34

0.00

0.02

0.04

0.06

0.08

nano-second

Thanks for your attention

Our laser is uniquely suited for coherent multi-photon process

fn=n-

I(f)

f

fn= n

Apply Physics B 92, 13-18 (2008)

PMT

Lock-in amplifier

AOM

Spatial light modulator

grating

-metal (3 layers)

chopper

Solenoid coilgrating

Cs cell

(Wall temperature 100 0.0010C)C)

1/4 852 nm

Pump laser

Synthesizer

Function Generator

Loran-C

Comb laser

PZT

CTSDL

Control fn

Control frep

Spectrum analyzer (FFT)

Repetition rate

Monitor fn, frep

PD

Submit to PRL

experimental results

repetition rate 1/100 clock frequency (Hz)

-0.8 -0.6 -0.4 -0.2 0.0 0.2 0.4 0.6 0.8

Fluo

resc

ence

(A

rb. u

nit)

0.95

0.96

0.97

0.98

0.99

1.00

1.01

70 Hz

1500 Pascal N2+1500 Pascal He, mixed buffer gas

))(( beatCos iR

H=H0+HEM

Dressed atom

a

b

+ Hde

radiative collision

Not a stable mixed state

c

Brief introduction on Coherent Population Trapping (CPT)

22

12

12

RR

RR cb

Ground state

Not dipole allowed transitionClock frequency

PMT

Lock-in amplifier

AOM

Spatial light modulator

grating

-metal (3 layers)

chopper

Solenoid coilgrating

Cs cell

(Wall temperature 100 0.0010C)C)

1/4 852 nm

Pump laser

Synthesizer

Function Generator

Loran-C

Comb laser

PZT

CTSDL

Control fn

Control frep

Spectrum analyzer (FFT)

Repetition rate

Monitor fn, frep

PD

Problems of CPT clocks

1. light shift and laser power broadening problem

2. need narrow linewidth as a frequency discriminator

3. buffer gas caused pressure shift

a

ba

bH0=

a

b0

0

c

0

0

00 c

c

HEM= 0

0

0

0 0

*1R

1R

*2R

2R

Hde= 0

0

0

0

0bc cb0

0

CW CPT86 kHz

without buffer gasCW CPT

with buffer gas

150 Hz

0 500 1000 1500 2000 2500 3000

0

200

400

600

800CW-light shift

comb-light shft

laser power (W)

ligh

t shi

ft (

Hz)

Power insensitive character of comb-CPT (1)

Viewpoint in time domain

Laser pulse

Atom /

molecule

Dressed

Atom/molecule

Mixed state

)()( tat nn

n

Time

1 ps 1 ps

10 ns

1 ps

10 ns

1 ps

10 ns

dressed wavefunction relaxes at quantum beat (clock frequency)

Theoretical simulation

CW-CPT (140 W)

500 Hz

-1.5 1.5-1 1-0.5 0 0.5

Nor

mal

ized

upp

er-l

evel

po

pula

tion

Detuning from clock frequency (kHz)

Comb-CPT (140 W)

40 Hz

-0.4 -0.2 0 0.2 0.4

Nor

mal

ized

upp

er-l

evel

po

pula

tion

Detuning from clock frequency (kHz)

Due to quantum interference effect

Comb laser

CW laser

CW-CPTPower broadening (with buffer gas)

CW-CPTLight shift (with buffer gas)

-80 -60 -40 -20 0 20 40 60 80

0.95

0.96

0.97

0.98

0.99

1.00

1.01F

luor

esce

nce

(Arb

. uni

t)

Detuning from clock frequency (mHz)

5.6 Hz Comb-CPT (with buffer gas)2-order of magnitude narrower linewidth2-order of magnitude improved light shiftinsensitive to pressure shift

45 Hz shift

950 Hz linewidth

0.8 Hz shift

Peak power: 1400 mW/cm2

Kinetic energy of Ne collision cell~0.1 eV

a

b

c

852 nm, 1.46 eV

1 ps100 mW/cm2

(peak power)

Ne

Effective collision time: 0.3 ms

CPT signal quenched

One-photon saturation power(1 mW/cm2)

6D3/2

8S1/20.2 eV

852 nm

Apply Physics B 92, 13-18 (2008)

Pump laser PZT 1

Ti:S crystal

PZT 2

Output coupler

Translational stage

prism 1

prism 2

A novel way on orthogonally controlling carrier-envelop phase

0 2 4 6 8 103.54.04.55.05.56.06.57.07.5

0 2 4 6 8 103.54.04.55.05.56.06.57.07.5

fn dither width (MHz)

Max

imum

f rep

fluc

tuat

ion

(m H

z)