Generation of coherent terahertz radiation based on CO2 laser mixing and its

application to molecular spectroscopy of interstellar species

Fusakazu Matsushima

Department of Physics,University of Toyama, Japan

KAGRA face to face meeting,,Kashiwa, July 31, 2012

Univ. of Toyama and KAGRA Group Joint workshop

July 7, 2012 in Toyama

Many staffs in the faculties of science and engineering have much interest in KAGRA project.

Now organizing researcher groups in Toyama U.. Coming Soon !!

Microwave Physics Lab.

Control of motion of molecules using Microwave → ultracold molecule

→ fundamental physicselectric dipole moment of electrontime evolution of fundamental constants

Spectroscopy of interstellar molecules

Laser Physics Lab.

Atoms/molecules in liq. He

Generation / selection of cold molecules

Terahertz spectroscopy of molecules ←

in my talk

1. Importance of the precise measurements in the far-infrared (terahertz) region

2. TuFIR spectrometer (CO2 laser difference frequency) 2-1. Principle 2-2. Application to molecules

HeH+, OH-, H2D+, H2O (vibrational excited state)

1. Importance of the precise measurements in the far-infrared (terahertz) region

Terahertz spectroscopy

Wide scan spectrograph. for: Biological substance Non-destructive inspection

High resolution spectroscopy

Guanine

frequency

Target of the high precision / high resolution spectroscopy of moledules in the THz region

Rotational spectra of light molecules2 or 3 atomic molecules including hydrogen

　 ex. water, 　 H2D+

　　　 ● astronomy, 　　　　　 ● remote sensing of atmosphere ●"test stone" for newly proposed theories

Vib. Spectra of molecules with internal rotation　　　 ex. methanol

　　 Spectra with large amplitude vibration, inversion ex. Chain molecule

Vib. Rot spectra of molecular clustersH2O, CO, N2 　．．．

　　　　　　　　　　　　● interface of gas phase and condenced phase

Terahertz spectroscopy

Herschel 　 Satelite 3.5m telescope, 2008 launch, 　 57 － 670μm

ALMA (Atacama Large Millimeter/submillimeter Array) 　　 30GHz to 950GHz 　 operation about 50 years from 2012

SOFIA (Stratospheric Observatory for Infrared Astronomy) 　 2.5m telescope on air craft (B747) 　 from 2007　　 8 hours per mission, 120 mission per year, operate 20 years　　 colaboration of the US (80%) and Germany (20%)　　１－６００ μm, 　 Hot Water, Carbon Chemistry

weedsCH3OH (CH3 internal rotation) Freq. Table up to 1THzHCOOCH3 　 (CH3 int. rot.) 　 Table up to 1.67THz, need for precisionCH3OCH3 (two int. rot.) Table up to 2.17THz, need for precisionCH3CH2CN (heavy mol.) Table up to 3.39THz, need for precisionSO2 　 (heavy mol.)

flowersH2O, O2, CO, ionic species

Accuracy needed ： better than １００ｋＨｚ .Want for data of vib. excited state.

International projects are in progress !

2. TuFIR spectrometer (CO2 laser difference frequency)

2-1. Principle

2-2. Application to molecules (mainly molecular ions)HeH+, OH-, H2D+

H2O (vibrational excited state)

0.3

TuFIR

from Matsui

μW

ｎ W

ｍ W

THz sources

gyrotron

Photo mixermultiplier

solid state

gas laser

TuFIR spectrometer

FIR=|I - II|±MW

CO2 laser lines

10P

10R

9P

9R

angle of grating

outp

ut p

ower

upper or lower sidebanddifference freq. of two CO2 lasers

Fourier transform spectrometer

TuFIR

MIM diode

micro wave

whisker

roof top mirror

base

FIR

CO2 laser

MIM diode as detector / mixer

Chain for the measurement of CO2 laser frequency

Standard:Cs atomic clock

MIMdiode

whisker

TuFIR spectrometer

FIR=|I - II|±MW

CO2 fluorescence cell

Laser frequency　 (cavity length)

4.3mfluorescence

1st derivative

Stabilization of the CO2 laser frequency

Accuracy of stabilization

Accuracy of one CO2 laser 25kHz

Accuracy of difference freq. 36 kHz

Data points are fitted with a theoretical curve (Voigt profile) determine the center frequency

Fig.1 TuFIR 分光計frequency range: up to 6THz

precision of the source: about 30 kHz

power: several tens to several hundreds nW

F1

F2

Fmw

F

Molecules and ions measured with TuFIR spectrometer in Toyama

(1) neutral molecules , radicals　　 LiH, KH, １８ OH, NH

　　 H2O (including isotopes, vibrationally excited state)

(2) molecules with internal rotation

　　 CH3OH

(3) cation protonated rare gas atoms 　　 (HeH+ ， NeH+ ， ArH+ ， KrH+ ， XeH+ ， including their isotopic species)

H2D+

(4) anion　　 OH- ， OD-

Fig.1 TuFIR 分光計

Velocity modulation:

detects ions only

Configuration for detecting ionic speciesion

HeH+

HeH+ J=10

The lowest frequency rotational line

2010.1839 (2) GHz

HeH+

HeH+ 　 Rotational Transition

transition frequency obs-calc

4HeH+ J=10 2010183.873 (202) 0.108J=21 4008733.084 (194) -0.148

4HeD+ J=21 2434626.571 (143) 0.077 J=32 3641427.274 (384) -0.210

J=43 4835691.417 (166) 0.039

3HeH+ J=10 2139522.472 (300) -0.213J=21 4265839.060 (300) 0.330

3HeD+ J=21 2696099.975 (255) -0.021 J=32 4031223.001 (511) -0.650

HeH+

Dunham coefficient Ykl 　

EvJ = ΣYkl(v+1/2 )k[J(J+1)]l

( a set of coefficientsYkl for each isotope)

To calculate all the isotopes with a set of coefficients Ukl

Ykl 　＝　 μ-(k/2+l)Ukl

Reduced mass μis not enough to fit all the isotopes.

Ykl 　＝　 μ-(k/2+l)Ukl [1+meΔHekl/MHe + meΔH

kl/MH] Correction terms usingΔvalues are necessary.

Breakdown of Born-Oppenheimer approximation.

HeH+

Delta coefficients included for HeH+

(v+ 1/2)k[J(J+1)]l

l 0 1 2 3 4 k

0 U Δ He U U U Δ H Δ H

1 U Δ He U U U Δ H

2 U U U U

3 U

HeH+

J =3← 2

3363550.5413363550.541 　　 　　 frequency frequency （（ MHzMHz ） 　　） 　　 3363658.5413363658.541intensity(arb. units)

intensity(arb. units)

OH-

transition frequency (MHz) J=43 4478174.516 (387) J=32 3363607.066 (238) J=21 2244776.819 (240) J=10 1123100.985 (324)

OD-

Frequency(MHz)

Frequency(MHz)Frequency(MHz) Frequency(MHz)

Frequency(MHz)

　 J=2←1 　 J=3←2

　 J=5←4 　 J=6←5 　 J=8←7

Inte

nsi

ty

(arb

.un

its)

Inte

nsi

ty

(arb

.un

its)

Inte

nsi

ty

(arb

.un

its)

Inte

nsi

ty

(arb

.un

its)

Inte

nsi

ty

(arb

.un

its)

D2O/O2=54.5/5Pa,AC1.2kHz,1.1A,4.8kV,Scan6 回 ,エタノール冷却 2 ,℃ 湿度 60%,FIR200mV( 100nW)≒

ND3/O2=35/10Pa,AC1.2kHz,1.0A,5.6kV,Scan3 回 ,水冷 , 湿度 29%,FIR140mV( 70nW)≒

ND3/O2=35/10Pa,AC1.2kHz,1.0A,5.6kV,Scan3 回 ,水冷 , 湿度 26%,FIR160mV( 80nW)≒

D2O/O2=23.5/5Pa,AC1.2kHz,1.2A,4.5kV,Scan3 回 ,水冷（溜め置き） , 湿度 60%,FIR150mV( 75nW)≒

ND3/O2=35/10Pa,AC1.2kHz,1.0A,5.6kV,Scan3 回 ,水冷 , 湿度 24%,FIR40mV( 20nW)≒

Fit 1196791.042(0.486)MHz

OH-, OD-

Evolution ofinterstellar molecules

typical trace of H2D+

211 110

H2D+

H2D+

Rotational spectra of water in the Sun spectra

　　　 1995 　 L. Wallace et al. “Water on the Sun”, Science, vol.268, pp.1155-1158, May 1995

Spectroscopy in the laboratory

　　　 Flame sample　　　 Emission from discharge cell

IR, FIR Fourier transform

H2O

Spectra near the Sun spot 　 (L. Wallace 1995)

＊ lines of water(Even the rotationallines in the v=0 state,high J lines cannotbe calculated noridentified.)

H2O

Normal modes of water molecule

H2O

Frequency (MHz)

423414 line in the (1,1,0) vibrational state

Energy of the 414 level: 5457.4 cm-1

H2O

END