Champaign, June 2015 Samir Kassi, Johannes Burkart Laboratoire Interdisciplinaire de Physique, Université Grenoble 1, UMR CNRS 5588, Grenoble F-38041, France

Very high sensitivity for both low concentrations & weak lines detection Fundamental and Applied Spectroscopy Tools & databases

2% absorption from earth to moon are equivalent to…a km cell! ~ 30 cm 30 cm meter on earth Cavity Ring Down Spectroscopy

Cavity enhanced techniques: what sensitivity limits? (according we have good mirrors)

First issue : photon shot-noise An efficient laser-cavity light coupling is needed to enhance performances Laser  ~2 MHz N photons S/B = N 1/2 quantum limit =1.5 µm N~ photons/s Sampling at 1 Ms/s Within 1µs ~ 10 7 photons collected Maximal S/N = mW 1 µW  ~2 kHz

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 Laser The laser drasticaly narrows… with almost no effort. 2 MHz 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).

Frequency / time Power Optical feedback Laser < Hz 150 MHz The laser frequency literaly jumps from mode to mode It is inherently “frequency agile” What happens as the laser is tuned?

Going further : separate laser source and gas cell Laser Ctrl Fiber Coupling Gives a stable & narrow laser Gives a high S/N The OFFS-CRDS

Going further : tunability frequency shifted output 0° 90° ν RF RF synthesizer isolator Fiber coupling DFB laser photo- diode optical feedback reference cavity temperature stabilized vacuum chamber PZTPZT ν n +ν RF servo loop νnνn νnνn Mach-Zehnder modulator Frequency ≈ 186 THz Linewidth < 500 Hz Drift < 20 Hz/s Tunability = 1 THz Opt. Lett. 38 (12), 2013 Single side-band modulator

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 2x cm -1 Hz -1/2 Opt. Lett. 38 (12), 2013

Spectrum of carbon dioxide (10 Pa) nm nm spectrometer dynamic range > · cm -1 RMS

Test of advanced line profiles Appl.Phys.B 119, (2015) CO 2 broadened by N 2 P T =150 Pa P CO2 = 0.75 Pa

Application to spectroscopy of CO 2 J.Chem. Phys 142, (2015)Appl.Phys.B 119, (2015) With M. Marangoni and T. Sala Politecnico di Milano

Application to spectroscopy of CO 2 J.Chem. Phys 142, (2015)Appl.Phys.B 119, (2015) With M. Marangoni and T. Sala Politecnico di Milano 6 kHz RMS

Saturated absorption – Lamb dip with 0.25 Pa CO 2 – 40 kHz frequency steps on 15 MHz span (≡ 1 minute scan) 160 μW input power ─ intracavity peak intensity > 1 kW/cm 2 SNR ~ 50 ↔ line center retrieval at 2 kHz precision (3) ← P(16) line Opt. Lett. 39 (16), 2014

Saturated absorption – Lamb dip with 0.25 Pa CO 2 – Burkart et al., J.Chem. Phys 142, , 2015

J. Burkart Thesis manuscript (2015) Saturated absorption – Full data treatment – Unsaturated part from non exponential fit Measurement with pure exponential fit

Towards Sustainable Spectroscopy Shot Noise limited absolute frequency broadband saturated spectroscopy… is on the way !

The (almost) full team Thank you for your attention!