1 / 15

P. Maddaloni National Institute for Applied Optics, Naples (Italy)

High-resolution and high-sensitivity spectroscopy of methane by means of a mW-power DFG spectrometer around 3.3 m m. P. Maddaloni National Institute for Applied Optics, Naples (Italy). CLEO Europe – EQEC Munich, 12-17 June 2005. Outline. INTRODUCTION The experimental apparatus

stasia
Download Presentation

P. Maddaloni National Institute for Applied Optics, Naples (Italy)

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. High-resolution and high-sensitivity spectroscopy of methane by means of amW-power DFG spectrometer around 3.3 mm P. Maddaloni National Institute for Applied Optics, Naples (Italy) CLEO Europe – EQEC Munich, 12-17 June 2005

  2. Outline INTRODUCTION The experimental apparatus Characterization of the source • METHANE SPECTROSCOPY • High resolution • Saturated absorption spectroscopy • High sensitivity • ICOS with a high-finesse cavity in off-axis configuration

  3. Motivations BS Laser 1 Crystal Laser 2 M • Most molecular species exhibit very strong ro-vibrational transitions between 2.9 and 3.5 mm  • high sensitivity • lower saturation intensities (frequency-reference grid) Wide tunability Mode-hop-free operation Narrow linewidth periodically poled crystals  much more efficient conversion

  4. The main ingredients • PUMP SOURCE • ECDL (few mW) + Yb fiber amplifier: 1026-1070 nm; up to 700mW; <1 MHz linewidth • Coarse tuning by diffraction grating • Temperature tuning: 0.3 nm/K • PZT: 300 MHz/V • SIGNAL SOURCE • Erbium fiber laser: 1545-1605 nm; up to 5W; <1 MHz linewidth • Coarse tuning: 0.8 nm step MULTIPLE CHANNEL PPLN L=29.6–30.6 mm; T=50-68 °C l=5 cm; h=w=1 mm IDLER RADIATION2.9-3.5 mm

  5. InSb detector InSb array 320*256 30-mm pixel The DFG set-up idler beam

  6. Characterization of the spectrometer • Control of the spatial beam profile  • efficient coupling to high-finesse cavities • excitation of very narrow transitions

  7. Sub-Doppler spectroscopy of methane pump beam 2.5 mW probe beam 1.4 mW dia. = 1 mm G = 1 MHz d = 2.86E-31 C·m  Is = 1 mW/mm2 P = 30 mTorr (L = 50 cm)

  8. Results n3 stretching mode phase-sensitive detection Fm = 3.5 kHz, Am = 5 MHz det. BW = 40 Hz R(4) E 3067.2344 cm-1 R(4) F1(2) 3067.2610 cm-1 S = 4% FWHM = 2.5  0.5 MHz det. BW = 1 kHz DFG emission linewidth pressure broad.  200 kHz transit-time broad.  500 kHz

  9. High-sensitivity spectroscopy RESONANT-COUPLING METHODS (ON-AXIS ALIGNMENT) lock the laser to a single resonance mode of the cavity decrease in FSR (extremely dense-mode spectrum)  cavity transmission very effectively averaged OFF-AXIS ALIGNMENT “transmission is frequency independent (solely determined by the round-trip cavity loss)” • Advantages • no need for complex components and sub-ms time-resolved measurement • lower sensitivity to vibration and misalignment •  in-situ trace-gas monitoring Drawbacks lower power transmission  a higher power is required

  10. ICOS set-up R = 99.95% (r = 6 m) Leff = d/(1-R) = 2 km

  11. FSRoff = FSRon/nre nre = 11.07 Off-axis cavity transmission scan interval=400 ms transmission exhibits large peak-to-peak intensity fluctuations FSR=15 MHz • reduce scan interval (4 ms) • modulate laser frequency (Am = 25 MHz, Fm = 10 kHz) • modulate cavity length (Am = 4.5 GHz, Fm = 410 Hz) intensity fluctuations are dramatically reduced by time-integration (det. BW = 6 Hz)

  12. CH3D CH4 Absorption spectra isotope detection in pure methane 2960.617586 cm-1; 2960.655300 cm-1 a(CH4) = 3.410-5 cm-1torr-1 P = 0.1 torr det. BW = 6 Hz acquisition time = 4 s

  13. P=1 atm P=50 Torr det. BW = 6 Hz acquisition time = 4 s nmin = 1 ppb/Hz Absorption spectra methane detection in ambient-air (n = 2 ppm) n = 2943.107924 cm-1 ; S = 8.410-20 cm/mol

  14. Conclusions and perspectives Sub-Doppler spectroscopy of methane Absolute frequency measurements (phase-lock to “Comb”) Cavity enhanced spectroscopy isotope detection in pure methane detection of methane in ambient-air WM and/or two-tone FM spectroscopy Portable all-fiber MIRTuS Sensing in liquid samples by fiber-loop ring-down spectroscopy

  15. National Institute for Applied Optics Laboratory team G. Gagliardi research scientist P. Malara PhD student P. De Natale research director P. Maddaloni research scientist

More Related