White powder identification using broadband coherent light in the molecular fingerprint region

Mid- to long-wave infrared computational spectroscopy with a graphene metasurface modulator

In recent years there has been much interest concerning the development of modulators in the mid- to long-wave infrared, based on emerging materials such as graphene. These have been frequently pursued for optical communications, though also for other specialized applications such as infrared scene projectors. Here we investigate a new application for graphene modulators in the mid- to long-wave infrared. We demonstrate, for the first time, computational spectroscopy in the mid- to long-wave infrared using a graphene-based metasurface modulator. Furthermore, our metasurface device operates at low gate voltage. To demonstrate computational spectroscopy, we provide our algorithm with the measured reflection spectra of the modulator at different gate voltages. We also provide it with the measured reflected light power as a function of the gate voltage. The algorithm then estimates the input spectrum. We show that the reconstructed spectrum is in good agreement with that measured directly by a Fourier transform infrared spectrometer, with a normalized mean-absolute-error (NMAE) of 0.021.

Mid- to long-wave infrared computational spectroscopy using a subwavelength coaxial aperture array

Miniaturized spectrometers are advantageous for many applications and can be achieved by what we term the filter-array detector-array (FADA) approach. In this method, each element of an optical filter array filters the light that is transmitted to the matching element of a photodetector array. By providing the outputs of the photodetector array and the filter transmission functions to a reconstruction algorithm, the spectrum of the light illuminating the FADA device can be estimated. Here, we experimentally demonstrate an array of 101 band-pass transmission filters that span the mid- to long-wave infrared (6.2 to 14.2 μm). Each filter comprises a sub-wavelength array of coaxial apertures in a gold film. As a proof-of-principle demonstration of the FADA approach, we use a Fourier transform infrared (FTIR) microscope to record the optical power transmitted through each filter. We provide this information, along with the transmission spectra of the filters, to a recursive least squares (RLS) algorithm that estimates the incident spectrum. We reconstruct the spectrum of the infrared light source of our FTIR and the transmission spectra of three polymer-type materials: polyethylene, cellophane and polyvinyl chloride. Reconstructed spectra are in very good agreement with those obtained via direct measurement by our FTIR system.

Generation of mid-infrared emission with a 3.1-4.5 μm instantaneous bandwidth from a chirped-pulse optical parametric oscillator

We report a broadband optical parametric oscillator (OPO) pumped by a Yb-doped fiber laser system. By utilizing a 300 μm long magnesium-doped periodically poled LiNbO₃ crystal as the parametric gain medium and configuring the OPO as a chirped-pulse oscillator, we obtained mid-infrared emission having an instantaneous bandwidth covering 3084-4466 nm. This result represents, to the best of our knowledge, the widest instantaneous bandwidth obtained from a Yb-fiber-laser-pumped singly resonant OPO, demonstrating the immense potential of chirped-pulse oscillation in scaling the instantaneous bandwidth of ultra-fast OPOs. Moreover, we performed a numerical simulation of chirped-pulse OPOs (CPOPOs) and revealed that the spectral profile of the output from a CPOPO was relevant to both the parametric gain profile of the nonlinear crystal and the intra-cavity high-order dispersion.