FASSST Cavity Ringdown Spectroscopy of Atmospherically Broadened Lineshapes in the Millimeter Spectral Region Corey Casto Frank C. De Lucia The Ohio State University International Symposium on Molecular Spectroscopy on Molecular Spectroscopy 63 rd Meeting — 16-20, 2008

Outline Introduction Experiment Cavity losses Water Continuum Carbon Monoxide Ozone Conclusions

Introduction What I mean by: Ringdown  = 1/c  RD Atmospherically broadened lines  ~ 100MHz-1GHz Millimeter region = GHz

Introduction Gases of interest: H 2 O –Abundant –Strong lines at millimeter frequencies –Strong continuum absorption CO –Close lines of different isotopologues –No line mixing –Compare to O 3 O 3 –Dense spectrum –Strong lines –Possible line mixing

Experiment Long cavity characteristics o ~6000 resonances o FSR = 14.5 MHz o  RD ~ 5  s o Q ~ 7x10 6 Short cavity characteristics o ~3000 resonances o FSR = 26.3 MHz o  RD  ~ 2  s o Q ~ 3x10 6 BWO Quasi-Optical Isolator Mylar® beam splitter Output Coupling Hole InSb Detector Vacuum Chamber DAQ Pulse Generator HV Power Supply 10.3 m 5.7 m Flip mirror

Cavity losses Sources of vacuum absorption: o Diffraction o Reflection o Coupling

Water P dry = 760 torr P water = 2.457(1) torr T = 23.3 C  cont = 2.774(3)x cm -1 GHz -2 VVW lineshape JPL line strength Largest residual near line peak

Water continuum At 23C  cont /P dry P H2O ~1.5x cm -1 torr -2 Nonlinearity and noise are worse for short cavity Water sticking to mirror

Carbon monoxide P dry = 383 torr P CO = 2.906(1) torr T = 23.1 C VVW lineshape JPL line strength Largest residual near line peak

Ozone P dry = 406 torr P ozone = 194.6(2) mtorr T = 23.2 C  cont = 3.42(5)x cm -1 GHz -2 VVW lineshape JPL line strengths HITRAN line broadening parameters Largest residual between strong lines o Broadening parameters o Line mixing

Ozone P dry = 102 torr P ozone = 190.8(1) mtorr T = 23.1 C  cont = 3.42(5)x cm -1 GHz -2 VVW lineshape JPL line strengths HITRAN line broadening parameters Largest residual near strong peaks o Broadening parameters o Line mixing

Ozone P dry = 117 torr P ozone = 262.2(3) mtorr T = 20.4 C  cont = 3.21(1)x cm -1 GHz -2 Formic acid Formaldehyde Water Other contaminants

Ozone Ozone pressure reached 241mtorr; dropped to 232mtorr o Diffusion o Decay Contaminant continuum absorption is linear in time ~8.0x cm -1 GHz -2 s -1

Ozone Ozone pressure reached 214mtorr; dropped to 166mtorr –Faster diffusion –Decay Contaminant continuum absorption is linear in time ~4.8x cm -1 GHz -2 s -1

Future H 2 O –Closer study of water sticking to mirror surfaces is needed O 3 –Reduce reactivity Remove reactive materials Reduce temperature –Cover full range of: Atmospheric pressures Ozone concentrations Atmospheric temperatures

Thank You