Time Evolution of Coherent Excitation (STIRAP)

Time Evolution of Coherent Excitation (STIRAP)

How Camp

7 April, 2004

How Camp

7 April, 2004

What is Coherent Excitation?What is Coherent Excitation?

0.5

1.0

Ex

cite

d p

op

ula

tio

n

Incoherent

Coherent

ARP

0.0|1>

|2>

I

Rabi Period

Time

2-Level

0.5

1.0

0.0

|1>

|3>

3-Level

|2>

Pump

StokesRab

i F

req

uen

cy

Time

Stokes Pump

What is STIRAP?What is STIRAP?E

xcit

ed F

ract

ion

Time

0

1

|1>

|2>

|3>

ApplicationsApplications

• Control of Chemical Reactions

• Atom Optics

• Laser Cooling

• Measurement of Weak B-Fields

• Cavity QED

• BEC From Bergmann, et al. Annu. Rev. Phys. Chem. (2001)

Technique: What Others DoTechnique: What Others Do

5S1/2 F=3

Monitor 420 nm fluorescence from 6P-5S transition

5P3/2 F’=4

5D5/2 F’’=5

6P3/2

Stokes

Pump

Monitor 780 nm fluorescence from

MOT

780 nm

776 nm

85Rb

Problems:Problems:

5S1/2 F=3

Monitor 420 nm fluorescence from 6P-5S transition

5P3/2 F’=4

5D5/2 F’’=5

Stokes

Pump

Monitor 780 nm fluorescence from

MOT

780 nm

776 nm

• Inaccurate measure of 5S atoms

• Time resolution limited by lifetimes

• Inability to see all transitions

85Rb

6P3/2

Technique: What We Can DoTechnique: What We Can Do

5S1/2 F=2

5P3/2 F’=3

4D5/2 F’’=4

Stokes

Pump

780 nm

1529 nm • Accurate excited-state fractions

• Measure all 3 populations

• Monitor time-evolution of process (~2 ns resolution)

87Rb

What Theory PredictsWhat Theory Predicts

Stokes (L2)

Pump (L1)

4D

5P

5S

Delay = -30 ns

What Theory PredictsWhat Theory Predicts

Stokes (L2)

Pump (L1)

4D

5P

5S

Technique: How We Do ItTechnique: How We Do It

MOTRIMSMOTRIMS

Q-Value SpectraQ-Value Spectra

50 75 100 125 150

0

500

1000

1500

2000

2500

3000

3500

Co

un

ts

Q-Value (Channel)

5s-3p

4d-3d5s-3s

-5

-4

-3

-2

-1

0

4d 2D5/2

, 4d2D3/2

4f 2F7/2

, 4f2F5/2

4s 2S1/2

4p 2P1/2

, 4p 2P3/2

23Na

4s 2S1/2

3d 2D5/2

, 3d2D3/2

3p 2P

1/2, 3p

2P

3/2

3s 2S

1/2

12f

4d 2D3/2,5/2

5p 2P

3/2

5s 2S

1/2

87Rb

Pote

ntia

l Ene

rgy

(eV)

Hold That Thought!Hold That Thought!

Simplified Experimental SetupSimplified Experimental Setup

Ion Beam

Diameter: ~ 500 m

Pump Laser (L1)

Diameter: ~ 200 m

Stokes Laser (L2)

Diameter: ~ 350 m

MOT

Diameter: ~ 600 - 800 m

7 KeV Na+ Rb

STIRAP Laser TimingSTIRAP Laser Timing

Trapping Lasers ONStokes (L2) ON

~50 ns

Pump (L1) ON ~50 ns

Trapping Lasers ON

Trap Off Time: ~ 0.5 s

Total Period: 5 s

Correlating Q-Value & Laser TimingCorrelating Q-Value & Laser Timing

+ =

50 75 100 125 150

0

500

1000

1500

2000

2500

3000

3500

Cou

nts

Q-Value (Channel)

2D TAC Spectra

TAC SpectraTAC Spectra

Q-Value (Channel)

Tim

e (s

)

50 100 150

0.5

1.0

1.5

2.0

2.5

0.0

5s-3p 5p-3p 5s-3s

4d-3d4d-3s

5p-3p

Time Evolution of STIRAPTime Evolution of STIRAP

Future WorkFuture Work

• Explore Temporal Evolution of STIRAP:

• Pulse Delay

• Pulse Width

• Laser Intensity

• Laser Detuning

• See Rabi Flops ?!

New MOTRIMS!New MOTRIMS!

New MOTRIMS!New MOTRIMS!

New MOTRIMS!New MOTRIMS!

New MOTRIMS!New MOTRIMS!

New MOTRIMS!New MOTRIMS!

New MOTRIMS!New MOTRIMS!

New MOTRIMS!New MOTRIMS!

New MOTRIMS!New MOTRIMS!

New MOTRIMS!New MOTRIMS!

New MOTRIMS!New MOTRIMS!

New MOTRIMS!New MOTRIMS!

New MOTRIMS!New MOTRIMS!

How Do We Measure Q Value?How Do We Measure Q Value?

Q: energy defect

: Scattering angle (Lab frame)

Pr|| , Pr : parallel and perpendicular recoil momentum components

PP , PP’ : projectile momentum before and after the collision

Vp: projectile velocity

nc: number of transferred electrons

pp

pP’

pr

rp

rp

||

2|| 2

1PcrP VnPVQ

p

r

P

P

Chopping Our Lasers

-3 -2 -1 0 1 2 3-1000

0

1000

2000

3000

4000

5000-3 -2 -1 0 1 2 3

0

5000

10000

15000

5s-3p

5s-3sCo

un

ts

Q value (eV)

AOM Off

5p-3p5s-3s

5s-3p

5p-3d5p-4p

5p-4s

Co

un

ts

Tot

80 90 100 110 120 130 140 15030

40

50

60

70

80

90

100

110

120

130

140

150

Time of Flight difference (ns)

TA

C (

chan

nel)

1.000

1.433

2.053

2.941

4.214

6.037

8.649

12.39

17.75

25.44

36.44

52.21

74.81

107.2

153.6

220.0

100 200 300

0

60

120

180

Cou

nts

TAC (channel)

Capture from 5P Capture from 5S

Chopping Our Lasers