Spectroscopy with comb- referenced diode lasers Matt Cich, Gary V. Lopez, Philip M. Johnson, Trevor...
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Transcript of Spectroscopy with comb- referenced diode lasers Matt Cich, Gary V. Lopez, Philip M. Johnson, Trevor...
Spectroscopy with comb-referenced diode lasers
Matt Cich, Gary V. Lopez, Philip M. Johnson, Trevor J. Sears and Chris P. McRaven65th OSU International Symposium on Molecular Spectroscopy. Talk FD-11
Friday June 25th, 2010
Funding: Division of Chemical Sciences, Geosciences and Biosciences, US Department of Energy and the American Chemical Society, Petroleum Research Fund.
Aims and Opportunities
Detection and characterization of molecular species involved in combustion. We wish to understand their properties, investigate dynamics and reactivity, and calibrate theory.
Development of non-intrusive, sensitive, and specific experimental techniques is vital.
New technology presents opportunities for greatly enhanced precision and sensitivity for line positions and shapes and, potentially, for high sensitivity broad band measurements.
195739.6495135(80) GHz
Increasing the measurement precision
Plus, the measurement of the absolute frequency of the transitions is only good to the quality of the wavelength measurement, i.e. about 1 part in 108 or about 30 MHz.
We can use frequency comb-based techniques to address these issues.
Ring or extended cavity diode laser-based FM absorption: we wish to measure spectral splittings and line shapes to 0.1 MHz or better, but laser frequency drifts as the data are acquired can be 10x this.
7MHz FWHM
CH2 near 820 nm
Simplest ExperimentLock external laser to one comb component so its frequency is stable and precisely known.
Tune laser by slightly varying the comb repetition frequency so that each optical frequency tunes by n(Δωrep) and record an absorption spectrum.
ωopt= n ωrep + ω0
Block Diagram
EOM
/4 Plate Fabry-Perot Cavity
OpticalIsolator
Beam Splitter
1550nm LASER
CW Beat Detection
COMB
Wavemeter
Fiber
GPS
194 MHz
PDH detector
194 MHz Oscillator Coupler Delay
Mixer
Amplifier
Low pass filter
Diagnostics
PC
Photodiode detector
Photodiode detector
Laser PDH feedback
Acetylene
Optical AlignmentCable lines
Piezo
RF powerAmplifier
Lockbox
Amplifier
First measurements
Sub-Doppler absorption of a combination band vibration-rotation transition in C2H2.
Previously these transitions in acetylene were used as secondary frequency standards near 1.5 microns.
Extended cavity diode laser locked to a scanning comb component. 1.5 parts in 1012 absolute accuracy. Absorption in confocal cavity-type cell with cavity mode locked to scanning laser.
195739.6495135(80) GHz
Improve stability of cavity locking and modulate the laser to permit lock-in detection and improved signal to noise.
Investigation of potential analytical spectroscopy using overtone and combination bands in small hydrocarbon molecules. Incorporate collision cooled cell?
Future
Sub-Doppler spectra of radicals. (CH2, PbF)
New experiments to take advantage of the multiplex nature of comb sources, FT-comb designs for lower resolution studies.