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Samir Kassi, Johannes Burkart Laboratoire Interdisciplinaire de Physique, Université Grenoble 1, UMR CNRS 5588, Grenoble F-38041, France Champaign, June 2015 Fundamental and Applied Spectroscopy Tools & databases Very high sensitivity for both low concentrations & weak lines detection Cavity Ring Down Spectroscopy ~ 30 cm 30 cm meter on earth are equivalent to…a 400 000 km cell! Cavity enhanced techniques: what sensitivity limits? (according we have good mirrors) First issue : photon shot-noise Dn ~2 kHz Laser N photons Dn ~2 MHz 1 µW 1 mW =1.5 µm quantum limit S/B = N1/2 N~ 1013 photons/s Sampling at 1 Ms/s Within 1µs ~ 107 photons collected Maximal S/N = 3000 An efficient laser-cavity light coupling is needed to enhance performances Second issue : frequency noise The source frequency noise converts to amplitude noise in the line wings OFFS-CRDS addresses those two issues narrow but widely tunable source PDH-locked ultra-sensitive CRDS Optical feedback : narrowing the source 2 MHz 2 kHz Laser 2 kHz sub Hz B. Dahmani et al., Opt. Lett. 12, 876 (1987). P. Laurent et al., IEEE J. Quantum Electron. 25, 1131 (1989). S. Ohshima and H. Schnatz, J. Appl. Phys. 71, 3114 (1992). J. Morville et al., Appl. Phys. B 80, 1027 (2005). The laser drasticaly narrows… with almost no effort. Optical feedback Power Laser 150 MHz < Hz Frequency / time The laser What frequency happens literaly as the jumps laserfrom is tuned? mode to mode It is inherently “frequency agile” Going further : separate laser source and gas cell Laser Ctrl Gives a stable & narrow laser Fiber Coupling Gives a high S/N The OFFS-CRDS Going further : tunability servo loop DFB laser reference cavity optical feedback isolator RF synthesizer temperature stabilized vacuum chamber νRF 0° Fiber photodiode νn frequency shifted output Frequency ≈ 186 THz • Linewidth < 500 Hz coupling • Drift < 20 Hz/s 90° νn Mach-Zehnder modulator Single side-band modulator νn+νRF • Tunability = 1 THz Opt. Lett. 38 (12), 2013 Going further : sensitivity Stabilized Cavity Ring Down Opt. Lett. 38 (12), 2013 Going further : sensitivity Very close to the shot-noise limit and sensitivity of 2x10-13cm-1Hz-1/2 Opt. Lett. 38 (12), 2013 Spectrum of carbon dioxide (10 Pa) 7.5 nm with a single diode 2·10-12 cm-1 RMS 1616.0 nm 1608.5 nm spectrometer dynamic range > 1 000 000 Test of advanced line profiles CO2 broadened by N2 PT=150 Pa PCO2 = 0.75 Pa Appl.Phys.B 119, 97-109 (2015) Application to spectroscopy of CO2 With M. Marangoni and T. Sala Politecnico di Milano Appl.Phys.B 119, 97-109 (2015) J.Chem. Phys 142, 191103 (2015) Application to spectroscopy of CO2 6 kHz RMS With M. Marangoni and T. Sala Politecnico di Milano Appl.Phys.B 119, 97-109 (2015) J.Chem. Phys 142, 191103 (2015) Saturated absorption – Lamb dip with 0.25 Pa CO2 – 3001(3) ← 0000 P(16) line • 40 kHz frequency steps on 15 MHz span (≡ 1 minute scan) • 160 μW input power ─ intracavity peak intensity > 1 kW/cm2 • SNR ~ 50 ↔ line center retrieval at 2 kHz precision Opt. Lett. 39 (16), 2014 Saturated absorption – Lamb dip with 0.25 Pa CO2 – Burkart et al., J.Chem. Phys 142, 191103, 2015 Saturated absorption – Full data treatment – Unsaturated part from non exponential fit Measurement with pure exponential fit J. Burkart Thesis manuscript (2015) Towards Sustainable Spectroscopy Shot Noise limited absolute frequency broadband saturated spectroscopy… is on the way ! The (almost) full team Thank you for your attention!