Generation of coherent terahertz radiation based on CO 2 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 physics electric dipole moment of electron time 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 (CO 2 laser difference frequency) 2-1. Principle 2-2. Application to molecules HeH +, OH -, H 2 D +, H 2 O (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 molecules 2 or 3 atomic molecules including hydrogen ex. water, H 2 D +  ● 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 clusters H 2 O, CO, N 2 ．．． ● 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 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 weeds CH3OH (CH3 internal rotation) Freq. Table up to 1THz HCOOCH3 (CH3 int. rot.) Table up to 1.67THz, need for precision CH3OCH3 (two int. rot.) Table up to 2.17THz, need for precision CH3CH2CN (heavy mol.) Table up to 3.39THz, need for precision SO2 (heavy mol.) flowers H2O, O2, CO, ionic species Accuracy needed ： better than １００ｋＨｚ. Want for data of vib. excited state. International projects are in progress !

2. TuFIR spectrometer (CO 2 laser difference frequency) 2-1. Principle 2-2. Application to molecules (mainly molecular ions) HeH +, OH -, H 2 D + H 2 O (vibrational excited state)

0. 3 TuFIR from Matsui μW ｎWｎW ｍWｍW THz sources gyrotron Photo mixer multiplier solid state gas laser

TuFIR spectrometer FIR =| I - II |± MW

CO 2 laser lines 10P 10R 9P 9R angle of grating output power

upper or lower sideband difference freq. of two CO 2 lasers Fourier transform spectrometer TuFIR

MIM diode micro wave whisker roof top mirror base FIR CO 2 laser

MIM diode as detector / mixer Chain for the measurement of CO 2 laser frequency Standard: Cs atomic clock MIM diode whisker

TuFIR spectrometer FIR =| I - II |± MW

CO 2 fluorescence cell Laser frequency (cavity length) 4.3  m fluorescence 1st derivative Stabilization of the CO 2 laser frequency Accuracy of stabilization  Accuracy of one CO 2 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 H 2 O (including isotopes, vibrationally excited state) (2) molecules with internal rotation CH 3 OH (3) cation protonated rare gas atoms (HeH + ， NeH + ， ArH + ， KrH + ， XeH + ， including their isotopic species) H 2 D + (4) anion OH - ， OD -

Fig.1 TuFIR 分光計 Velocity modulation: detects ions only Configuration for detecting ionic speciesion

HeH+

HeH + J=1  0 The lowest frequency rotational line (2) GHz HeH+

HeH + Rotational Transition transition frequencyobs-calc 4 HeH + J=1  (202) J=2  (194) HeD + J=2  (143) J=3  (384) J=4  (166) HeH + J=1  (300) J=2  (300) HeD + J=2  (255) J=3  (511) HeH+

Dunham coefficient Y kl E vJ = Σ Y kl (v+ 1/2 ) k [J(J+1)] l ( a set of coefficientsY kl for each isotope) To calculate all the isotopes with a set of coefficients U kl Y kl ＝ μ -(k/2+l) U kl Reduced mass μis not enough to fit all the isotopes. Y kl ＝ μ -(k/2+l) U kl [1+m e Δ He kl / M He + m e Δ H kl /M H ] Correction terms usingΔvalues are necessary. Breakdown of Born-Oppenheimer approximation. HeH+

Delta coefficients included for HeH + (v+ 1/2 ) k [J(J+1)] l HeH+

frequency （ MHz ） intensity(arb. units) OH - transition frequency (MHz) J=4  (387) J=3  (238) J=2  (240) J=1  (324)

OD - J=2←1 J=3←2 J=5←4 J=6←5 J=8←7 Intensity (arb.units) D 2 O/O 2 =54.5/5Pa,AC1.2kHz,1.1A,4.8kV,Scan6 回, エタノール冷却 2 ℃, 湿度 60%,FIR200mV( ≒ 100nW) ND 3 /O 2 =35/10Pa,AC1.2kHz,1.0A,5.6kV,Scan3 回, 水冷, 湿度 29%,FIR140mV( ≒ 70nW) ND 3 /O 2 =35/10Pa,AC1.2kHz,1.0A,5.6kV,Scan3 回, 水冷, 湿度 26%,FIR160mV( ≒ 80nW) D 2 O/O 2 =23.5/5Pa,AC1.2kHz,1.2A,4.5kV,Scan3 回, 水冷（溜め置き）, 湿度 60%,FIR150mV( ≒ 75nW) ND 3 /O 2 =35/10Pa,AC1.2kHz,1.0A,5.6kV,Scan3 回, 水冷, 湿度 24%,FIR40mV( ≒ 20nW) Fit (0.486)MHz

OH-, OD-

Evolution of interstellar molecules

typical trace of H 2 D  1 10 H2D+

Rotational spectra of water in the Sun spectra 1995 L. Wallace et al. “Water on the Sun”, Science, vol.268, pp , 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 rotational lines in the v=0 state, high J lines cannot be calculated nor identified.) H2O

Normal modes of water molecule H2O

Frequency (MHz) 4 23  4 14 line in the (1,1,0) vibrational state Energy of the 4 14 level: cm -1 H2O

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