|
Ghost imaging is an active technique that implies using a time-varying structured illumination source to image a target without spatially-resolving measurements of the light beam that interacts with the target. Traditionally, a beam splitter is used to create two highly correlated beams, such that the signal interacts with the target and is then measured by a single pixel detector, while the reference is directly measured by a spatially resolving detector. This approach allows to implement ghost imaging in the space domain, nevertheless also temporal and frequency domains can be addressed1,2, allowing to extract the pertinent information. In particular, ghost imaging in the frequency domain has been recently applied to extract spectral information from a target object by means of Fourier Transform Interferometry3,4. In this work we illustrate and discuss the results of interaction-free measurements on an Er3+ doped nonlinear crystal, placed in one arm of an interferometer, obtained by using only non-interacting photons. Our equipment is a wave-guided solid state device, exploiting an integrated quantum photonic circuit that is equivalent to an Asymmetric Nonlinear Mach-Zehnder Interferometer. The experiment was performed by using a 250mW monochromatic 980 nm laser source that allowed exciting an Er:LiNbO3 waveguide, placed in one of the arms of the asymmetric interferometer. The interferograms were obtained by varying the signal in the time domain by using a LiNbO3 undoped waveguide in the opposite branch of the interferometer and recorder with a standard Si p-i-n detector, provided with a pass band filter (975nm ± 25nm) thus blocking all photons except the pump ones. The data were analyzed with conventional Fast Fourier Transform Techniques. The application of this approach allowed to recover information in the frequency domain, in particular, despite the monochromatic characteristics of the detected signal, we could recover the whole spectroscopy of the energy levels of the Er3+ doped crystal. The role of the converted photons was evidenced by the fact that, by using a radiation source that does not interact with the dopant (1320nm Laser), only the line of the source is recovered by the FFT handling of the interferograms. An important aspect to remark is that the obtained spectral distribution addressed also the IR part of the spectrum where the applied detector (Si p-i-n) is blind. In this view, this methodology opens the possibility to extend sensitive spectral measurements in spectral regions where detectors show poor responsivity.
|
