Spectral imaging at high definition and high speed in the mid-infrared

Abstract

Spectral imaging in the mid-infrared (MIR) range provides simultaneous morphological and chemical information of a wide variety of samples. However, current MIR technologies struggle to produce high-definition images over a broad spectral range at acquisition rates that are compatible with real-time processes. We present a novel spectral imaging technique based on nondegenerate two-photon absorption of temporally chirped optical MIR pulses. This approach avoids complex image processing or reconstruction and enables high-speed acquisition of spectral data cubes (xyω) at high-pixel density in under a second.

Wide-field mid-infrared hyperspectral imaging beyond video rate

“…The involved MIR source originates from a high-brightness supercontinuum fiber laser with spectral coverage from 1.9 to 3.9 μm 19 . The supercontinuum source eliminates the need for tuning operation as typically required for OPO sources 37 , 41 in broadband imaging. A long-pass filter is used to select the wavelength portion longer than 2.4 μm, as shown in Fig.…”

“…Figure 6 B shows a shadowgraph for the mixed liquid at the spectral channel of 3800 cm −1 for the frame n = 80. To better visualize the chemical differentiation, the dimensionality of the hyperspectral data stack can be reduced to two featured frames, where one sample appears transparent while another exhibits strong absorption and vice versa 41 . As illustrated in Fig.…”

“…In parallel, other promising architectures for indirect MIR imaging have also been intensively investigated by resorting to the photothermal effect within interrogated samples 6 , 38 , 39 or two-photon absorption (TPA) of the optical detector itself 40 , 41 . For instance, a wide-field photothermal microscope enables a chemical imaging speed at video rate 39 , albeit the spectral sweeping rate is hampered by the wavelength tuning time of the involved OPO source.…”

“…For instance, a wide-field photothermal microscope enables a chemical imaging speed at video rate 39 , albeit the spectral sweeping rate is hampered by the wavelength tuning time of the involved OPO source. Additionally, TPA-based spectral imaging at high definition is implemented by combining time-stretched spectroscopy and delay-scanning optical gating, which facilitates a 1.1-s acquisition time per spectral sweep over 530 cm −1 41 . In previous reports, the ultimate spectral imaging speed is impeded by deficiencies in rapid spectral filtering and/or fast wide-field detection, which is insufficient to observe transient phenomena and real-time processes.…”

Mid-infrared single-photon upconversion spectroscopy enabled by nonlocal wavelength-to-time mapping

“…In the frequency upconversion process, the quantum-correlated properties of MIR photons are well maintained. The conjugated NIR heralding photons from photon pairs are routed via a 10-km single-mode fiber (SMF) to acquire group velocity dispersion (GVD), enabling wavelength-to-time mapping (35)(36)(37)(38)(39). Because of the quantum correlation inherited by the upconverted photons, we successfully implement correlation measurement that nonlocally maps the spectral information contained by the MIR signal photons into the time domain.…”