FM1A.4.pdf
CLEO:2015 © OSA 2015
Quantum Refractometer Anna Paterova1, Dmitry Kalashnikov1, Sergei Kulik2, and Leonid Krivitsky1 1
Data Storage Institute, Agency for Science Technology and Research, 5 Engineering Drive I, 117608 Singapore 2 Department of Physics, Lomonosov Moscow State University, 119992 Moscow, Russia Author e-mail address:
[email protected]
Abstract: We exploit the first-order interference of two frequency non-degenerate Parametric Down Conversion (PDC) sources to observe resonant absorption of CO2 gas. Frequency correlations of PDC modes allow the detection of resonant absorption and dispersion of the infrared (IR) mode from interference patterns of visible light. This work demonstrates the determination of real and imaginary parts of the refractive index for IR wavelengths with conventional visible range optics and photodetectors. OCIS codes: (270.0270) Quantum Optics; (190.0190) Nonlinear optics; (300.0300) Spectroscopy;
1. Introduction The concept of nonlinear interference was introduced by Mandel in 1999 [1]. It is based on the interference of parametric down conversion (PDC) beams from two non-linear crystals. The resulting interference pattern depends on the total phase acquired by three interacting modes (the pump, the signal, and the idler) in the gap between the two crystals. In a particular case, when PDC is operated in the frequency non-degenerate regime, the interference pattern of the signal mode in the visible wavelength band depends on the phase of the idler photon in the infra-red wavelength band. In 2001 [2], this idea was used to measure dispersion from paraffin oil, and in 2014 [3] it was used for imaging phase objects. Here we measure real and imaginary parts of the refractive index of CO2 gas in vicinity of IR resonance, coinciding with an idler mode, by observing an interference pattern of the signal (visible) mode. 2. Experimental setup and Results Our nonlinear interferometer consists of a vacuum chamber with two LiNbO3 crystals, where PDC occurs. The distance between the two crystals is 25 mm and they are pumped by a cw laser at 532 nm. The interference pattern is observed by a spectrograph and a visible-light CCD camera. A frequency-angular spectrum of a signal mode in vacuum exhibits distinctive interference fringes centered at 604 nm, see Fig. 1(a). The frequency of the idler mode is chosen to coincide with the absorption resonance of CO2 at 4.3 μm. When CO2 is injected in the chamber, the visibility of the interference pattern decreases due to absorption of idler photons, see Fig.1 (b, c). Fringes also exhibit a phase shift due to resonant dispersion in the vicinity of the resonance, see Fig 1(c). By fitting the observed patterns for the signal mode at 604 nm, we are able to determine real and imaginary parts of the refractive index close to CO2 resonance at 4.3 μm. The approach does not require the use of IR optics and IR sensitive equipment.
Fig.1 Angular-frequency spectra of PDC for a signal mode at 0 Torr (a) and at 8.0 Torr (b) of CO2 gas. Frequency of the idler mode is tuned to coincide with the resonance absorption line of CO2 at 4.3 μm. The intensity cross-sections of (a, b) along white dashed lines are shown in (c) by red (for (a)) and black (for (b)) curves. Presence of CO2 results in degradation of visibility and in shift of interference fringes. This enables determination of a complex refractive index for the idler mode in IR from observation of the interference pattern of the signal mode in visible.
3. References [1] L. Mandel, “Quantum effects in one-photon and two-photon interference” Rev. Mod. Phys. 71, S274 (1999). [2] D. Korystov, S. Kulik, A. Penin “Rozhdestvenski Hooks in Two-Photon Parametric Light Scattering” JETP Letters 73, 214–218 (2001). [3] G. B. Lemos et al., “Quantum imaging with undetected photons” Nature 512, 409-412 (2014).
