Tunable optical coherence tomography in the infrared range using visible photons

Abstract

Optical coherence tomography (OCT) is an appealing technique for bio-imaging, medicine, and material analysis. For many applications, OCT in mid-and far-infrared (IR) leads to significantly more accurate results. Reported mid-IR OCT systems require light sources and photodetectors which operate in mid-IR range. These devices are expensive and need cryogenic cooling. Here, we report a proof-of-concept demonstration of a wavelength tunable IR OCT technique with detection of only visible range photons. Our method is based on the nonlinear interference of frequency correlated photon pairs. The nonlinear crystal, introduced in the Michelson-type interferometer, generates photon pairs with one photon in the visible and another in the IR range. The intensity of detected visible photons depends on the phase and loss of IR photons, which interact with the sample under study. This enables us to characterize sample properties and perform imaging in the IR range by detecting visible photons. The technique possesses broad wavelength tunability and yields a fair axial and lateral resolution, which can be tailored to the specific application. The work contributes to the development of versatile 3D imaging and material characterization systems working in a broad range of IR wavelengths, which do not require the use of IR-range light sources and photodetectors.

Polarization effects in nonlinear interference of down-converted photons

“…Further extension of the operating wavelengths of the presented methods can be easily achieved by choice of the periodic poling of the crystals and/ or by tuning crystal temperature. Operation within the range of 1,5-4,3 um was shown in our earlier works with LiNb crystals [15][16][17][18].…”

“…(2) changes. According to the beam splitter model [31], and assuming that idler modes i1 and i2 are matched, the photon annihilation operator for the idler mode i2 is given by: [17,18], we obtain the following expression:…”

“…When the unknown sample is inserted in the path of idler photons, one can infer its properties in the IR range from the interference pattern for signal photons in the visible range. This concept was recently implemented in several practical applications, including IR imaging [12], IR spectroscopy [13][14][15][16][17] and IR tunable optical coherence tomography (OCT) [18].…”

Fourier transform infrared spectroscopy with visible light

“…Nonlinear interferometers have recently sparked interest for their applications in quantum imaging [2,3], optical coherence tomography [4,5] and spectroscopy [6][7][8], allowing for measurements in the mid-infrared range by detecting entangled visible photons. They rely on spontaneous parametric down-conversion (SPDC), which can be described as the decay of a pump photon into two photons, called signal and idler, inside a nonlinear crystal.…”

Mid-infrared Frequency-domain Optical Coherence Tomography with Undetected Photons

“…To realise OCT in the mid-IR, while requiring neither mid-IR detection or laser source capabilities, one can exploit nonlinear interferometry with pairs of photons generated via spontaneous parametric down-conversion (SPDC) [21]. Recent works have considered this approach so far only in the context of time-domain OCT [22,23]. Also, these initial demonstrations proved comparatively slow and insensitive, realising only relatively low and practically insufficient axial resolutions of 500 µm at 1550 nm [22] and 105 µm in the mid-IR [23].…”