Fast Sweeping Double Resonance Microwave - (sub)Millimeter Spectrometer Based on Chirped Pulse Technology Brian Hays 1, Susanna Widicus Weaver 1, Steve Shipman 2 1. Emory University 2. New College of Florida

Microwave Double Resonance Spectroscopy Typically done using FTMW techniques to find connecting upper levels In a jet cooled experiment, can result in a near complete depletion of the MW signal J=0 J=1 J=2 mmW Pump MW Probe

MW-mmW Double Resonance Not previously done using mmW absorption as the detection frequency Could be used to find connecting states in sparse mmW spectra Increase speed of acquisition using fast sweeping methods J=0 J=1 J=2 mmW Probe MW Pump

Standard Double Resonance Schematic Microwave Synthesizer 23 – 40 GHz Hot Electron Bolometer x6 Microwave Synthesizer 8 – 18 GHz Amplifier Oscilloscope Backing Gas, Sample

Fast Sweeping Double Resonance Schematic Microwave Synthesizer 23 – 40 GHz Hot Electron Bolometer x6 Microwave Synthesizer 4 – 14 GHz Amplifier 6 – 18 GHz Digital Delay Generator LPF 0 – 5 GHz AWG 0 – 5 GHz Mixer Digitizer/Computer Backing Gas, Sample 10 MHz Clock

Fast Sweeping Double Resonance Schematic Microwave Synthesizer 23 – 40 GHz Hot Electron Bolometer x6 Microwave Synthesizer 4 – 14 GHz Amplifier 6 – 18 GHz Digital Delay Generator LPF 0 – 5 GHz AWG 0 – 5 GHz Mixer Digitizer/Computer Eccosorb 10 MHz Clock Backing Gas, Sample

Methanol Double Resonance MHz Pump MHz Probe 3 -1,3 2 -1,2 2 +0,2 J (E)Ka,Kc Detector Signal (V) Detector signal of methanol moving through the millimeter wave beam including a double resonance sweep. Downward signal is absorption from the methanol transition.

Methanol Double Resonance

Formaldehyde Double Resonance MHz Pump MHz Probe 2 1,1 2 1,2 1 1,1 J Ka,Kc The double resonance signal has a different phase than that observed in the methanol system.

Double Resonance Is power contributing to the phase difference? Attenuate the power to look for any change

Formaldehyde DR MHz MHz MHz 1 1, 0 1 1, 1 2 1, 1 2 1, 2 Probe: 2 1, , 1 Pump: 2 1, , 2 Probe: 2 1, , 0 Pump: 2 1, , 2

Methanol Double Resonance Fast sweep double resonance to observe phase change as a function of intensity MHz Pump MHz Probe 3 -1,3 2 -1,2 2 +0,2 J (E)Ka,Kc MHz Probe

Fast Sweep DR - Methanol

Fast Sweep Double Resonance The sign of the double resonance signal appears to be power dependent Valve conditions seem to affect them too Lines are very power broadened (~20 MHz FWHM) Takes 30 minutes for a broad scan (~10 GHz); previous experiments took several hours

Acknowledgements Widicus Weaver Lab Morgan McCabe NSF #CHE NSF #CHE

Formaldehyde DR MHz MHz MHz MHz MHz 1 1, 0 1 1, 1 2 1, 1 2 1, 2 3 1, 2 3 1, 3

Formaldehyde DR MHz MHz MHz 2 1, 1 2 1, 2 3 1, 2 3 1, 3 Probe: 3 1, , 1 Pump: 2 1, , 2 Probe: 3 1, , 2 Pump: 2 1, , 2