High Precision Mid-Infrared Spectroscopy of 12C16O2 : Progress Report Speaker: Wei-Jo Ting

Department of Physics National Tsing Hua University 2010.06.25Department of Physics National Tsing Hua University 2010.06.25

OutlineOutlinePrecision MIR source

• mW PPLN DFG source

• Frequency calibration

High resolution spectroscopy of CO2

• 0001← 0000 @ 4.3 μm (Fundamental ν3 band)

• [1001,0201]I ← 0000 band @ 2.69 μm

• [1001,0201]II ← 0000 band @ 2.76 μm

• 0111← 0110 @ 4.3 μm (Hot-band)

• [1110,0310]I ← 0000 band @ 4.8 μm

mW PPLN DFGmW PPLN DFG sourcesource

Ti:Sapphire laser

Nd:YAG laser MgO:PPLN

Temperature stability < 0.05 ℃

Ge plate

1 W tunable: 700 ~1000 nm

8 W though fiber amplifier @1064nm

DFG radiation 2 to 5 m ~7 mW @ 2.8 m

44 mm

Frequency calibrationFrequency calibration

• Ti:sapphire laser (fTiS) Optical Frequency Comb

• Nd:YAG laser (fYAG) Iodine hyperfine transition

fTiS- fYAG=fDFG DFG absolute frequency

OFCOFC performancesperformances

• Repetition frequency: 1 GHz • Average power of supercontinuum: 420 mW• Spectral range of supercontinuum: 500 ~ 1500 nm• Stability of repetition frequency: 0.68 mHz• Stability of offset frequency: 4 mHz• Accuracy: 10-12 @ 1 s (referenced to a GPS

disciplined Rb clock)

Why COWhy CO22? ?

• Most heterodyne frequency measurements are carried on CO2 laser transitions

A. G. Maki et al., J. Mol. Spectrosc. 167, 211 (1994)

A. Amy-Klein, H. Vigué, C. Chardonnet, J. Mol. Spectrosc. 228, 206 (2004)

• Only one measurement for [1001,0201]I← 0000 band

A. Groh et al., J. Mol. Spectrosc. 146, 161 (1991)

Energy diagram of COEnergy diagram of CO2 2

No good laser sources

Frequency measurement is difficult before OFC is invented

Fundamental vFundamental v33 band band:: Experimental set-up

CaF2 window

InSb detector

DFG

CO2 cell

Lock-in amplifier

Lock point

Fundamental vFundamental v33 band band

OSU ISMS 63th FA09

• 56 P- and R-branch transitions up to J=60 (accuracy < 30 kHz)

(see OSU 63th ISMS FA09)

• 10 high J (60<J<90) R-branch transitions (accuracy < 72 kHz)

(see OSU 64th ISMS TG11)

Molecular constants of the ground vibration level are greatly improved.

Fundamental vFundamental v33 band band

[10[10001,021,02001]1]I,III,II←← 00 00000 Bands: 0 Bands:

Saturated 4.3 Saturated 4.3 μμm Fluorescencem Fluorescence

• 2.7 μm laser pumping.• Probing 4.3 μm fluorescent signal.• Zero background, High S/N ratio.

Direct detection vs. Fluorescence detectionDirect detection vs. Fluorescence detection

Direct Detection Fluorescence Detection

OSU ISMS 63th FA10

• For [1001,0201]I ← 0000 , 19 transitions have been measured to an accuracy of 40 kHz

• Accurate molecular constants of the [1001,0201]I vibrational level have been determined

(see OSU 63rd ISMS FA10)

[10[10001,021,02001]1]II← 00← 00000 Band 0 Band

For For [10[10001,021,02001]1]II II ← 00← 00000 weaker band 0 weaker band

Old design New design

8.7 times enhancement

New design for fluorescence signal enhancement• Reduce the distance between L-cell and detector.• Use larger area InSb detector (diameter from 4 mm to 7 mm)

One order of magnitude improvement!

5500 6000 6500 7000 7500 8000 8500 9000 9500

-0.000010

-0.000005

0.000000

0.000005

0.000010

sign

al(m

V)

frequency(point)

Scan 0.5GHz300s50 point/sFWHM~233MHz20mm torrmod. amp 1.2V

[10[10001,021,02001]1]IIII ← 00 ← 00000 Band 0 Band

P(20)P(20) fluorescence signalfluorescence signal

Need more effort to enhance the signal…

• New focusing lens for

saturation intensity.

• Boost DFG Power

• Better light overlapping.

Hot Band: Hot Band: Signal enhancementSignal enhancement

• Quartz glass tube • Total Cell length: 60 cm • Nickel-Chromium wire heater wind over the cell

• Quartz glass tube • Total Cell length: 60 cm • Nickel-Chromium wire heater wind over the cell

HHot band signalot band signal

Third-derivative saturated absorption spectrum of 0111←0110 P(30) transition. The gas pressure was 30 mTorr at 700 K.

Weak transitions near 01Weak transitions near 01111-011-01110 P(30)0 P(30)

0 200 400 600 800 1000

-10.0

-7.5

-5.0

-2.5

0.0

2.5

5.0

7.5

10.0

L5L4

L3

Scan Frequency (A.U.)

-1000

-750

-500

-250

0

250

500

750

1000

L2

(b)

Thi

rd-D

eriv

ativ

e S

igna

l (V

)T

hird

-Der

ivat

ive

Sig

nal (V

)

(a)

L1

L1: 12C16O2 2001-2000 R(4)

L2: 16O12C18O 0111-0110 P(12)f L3: CO2 0111-0110 P(30)

L4: 16O12C18O 0111-0110 P(12)e L5: 12C16O2 0331-0330 Q(19)

Measurement resultsMeasurement results

TransitionThis work a

(MHz)HITRAN b

(MHz)Difference a － b

(MHz)12C16O2

0111-0110 P(30)69 267 228.761 (20) 69 267 225.23 -3.531

12C16O2

2001-2000 R(4)69266995.409 (95) 69266944.862 50.547

16O12C18O

0111-0110 P(12)f69267025.884 (139) 69266986.053 39.831

16O12C18O

0111-0110 P(12)e69267481.268 (151) 69267441.648 39.620

12C16O2

0331-0330 Q(19)69267536.410 (115) 69267857.700 - 321.290

Future works Future works

• High J transitions of fundamental band

• New measurements on

[1001,0201]II ← 0000 band

• More measurements on

0111 ← 0110 band (hot band)

• [1110,0310]I←0000 band

[11[11110, 030, 03110]0]II ←← 00 00000 band @0 band @ 4.8 4.8 μμmm

0111

0000

[1110,0310]I

0110

CO2 laser10.8 μm

Hot-band

16 μm

[1110, 0310 ]I ← 0000 band

• 1000 times weaker.

• 2075 cm-1 (4.8 μm)

• Cavity enhancement

[1110, 0310 ]I ← 0000 band

• 1000 times weaker.

• 2075 cm-1 (4.8 μm)

• Cavity enhancement

Thank Dr. Maki for valuable suggestions. He will also do the globe fitting after we finish all measurements

Thanks for your attention!