Synchrotron Far Infrared Spectroscopy Higher resolution and longer

Synchrotron Far Infrared Spectroscopy: Higher resolution and longer wavelengths at the Canadian Light Source A. R. W. Mc. Kellar National Research Council of Canada D. R. T. Appadoo Canadian Light Source (now at the Australian Synchrotron)

Where is Saskatoon?

CLS Parameters Energy: 2. 9 Ge. V Current: 200 m. A Circumference: 171 m 12 straight sections, 5. 2 m long RF: 500 MHz, 2. 4 MV, supercon Injection: 250 Me. V LINAC full energy booster ring Main building: ~ 85 x 85 m

Synchrotron IR There are two infrared beamlines at CLS: 1) Far IR (this talk) 2) Mid IR spectromicroscopy (biological / industrial samples) All other CLS beamlines are for x-rays The synchrotron replaces the normal source (globar), providing continuum IR radiation to a conventional FTIR spectrometer The high brightness of synchrotron radiation is ideal for the small entrance aperture required for high spectral resolution. But noise can be a big problem! Bruker IFS 125 HR spectrometer: max optical path difference = 9. 4 m; instrumental resolution ~ 0. 0006 cm-1 (18 MHz)

Clearly signal-to-noise ratio is the important factor Diamond Window Our problem is mechanical vibrations in the optics that bring IR radiation from the storage ring to the spectrometer Spectrometer Ring Source Shielding Wall

The vibrations tend to occur at particular acoustic frequencies (e. g. 120 Hz), and this ‘noise spectrum’ maps directly to our far-IR spectrum. By varying the mirror scan speed in the FTS, we can alter this mapping.

With successive improvements, the synchrotron now has a significant advantage over a globar from 100 ~ 800 cm-1 But we are aiming for much better performance • Reduce noise at source: better isolation of offending cooling pumps, heat exchangers, pipe runs, etc. • Reduce noise at beamline: more isolation, better mounting of mirrors • Active optics to stabilize the input radiation on the spectrometer aperture

Acrolein CH 2 CHCHO (propenal) A B 1. 57955 C 0. 14152 0. 15542 • fundamental 8 -atom species • planar near-prolate asymmetric rotor • interstellar molecule • combustion byproduct (cigarette smoke) • potent respiratory irritant (smog) low lying vibrational states of acrolein

17 band of acrolein, CH 2 CHCHO Ka = 7 – 6 Q-branch nominal resolution 0. 0012 cm-1

Acrolein 18 central region

Acrolein 18 central region

0. 3 m multi-pass gas cell absorption paths up to ~12 meters

2 m multi-pass gas cell absorption paths up to ~80 meters can be cooled to 200 K (or lower)

Acrolein 18 central region

Acrolein 18 central region

With 0. 0007 cm-1 line width and reasonable signal-tonoise ratio, line positions can be measured to <0. 0001 cm-1 (for unblended lines). Half of the acrolein lines here are measured to 0. 00003 cm-1 (1 MHz) or better.

CLS Acrolein Studies 12, 17 [600 cm-1 region] JMS 241, 31 (2007) 18 [150 cm-1 region] JMS 244, 146 (2007) all levels below 700 cm-1 JMS, in press (2008) 11, 14, 16, etc. [900 cm-1 region] H. -Y. Shi, L. -H. Xu, R. M. Lees see Paper TE-9

Coherent Synchrotron Radiation is what happens when the electron bunch length becomes comparable to the emitted wavelength

Coherent Synchrotron Radiation If the electron bunches in the storage ring can be made sufficiently short, then their synchrotron emission becomes coherent

Coherent Synchrotron Radiation is what happens when the electron bunch length becomes comparable to the emitted wavelength

Coherent Synchrotron Radiation tends to be noisy because of its nonlinear nature and the presence of beam instabilities (as if we didn’t have noise already)

High-resolution synchrotron IR There were previous results (MAXlab, LURE), but we are the first synchrotron user facility for highresolution IR spectroscopy of gases Soon there will be competition: SOLEIL, Australian Synchrotron, Swiss Synchrotron, Singapore, etc. Our beamline scientist, Dominique Appadoo, was lured to Melbourne for the Australian Synchrotron. His replacement, Brant Billinghurst, has recently joined CLS.