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.

Recent work on mid-infrared (MIR) detection through the process of non-degenerate two-photon absorption (NTA) in semiconducting materials has shown that wide-field MIR imaging can be achieved with standard Si cameras. While this approach enables MIR imaging at high pixel densities, the low nonlinear absorption coefficient of Si prevents fast NTA-based imaging at lower illumination doses. Here we overcome this limitation by using InGaAs as the photosensor. Taking advantage of the much higher nonlinear absorption coefficient of this direct bandgap semiconductor, we demonstrate high-speed MIR imaging up to 500 fps with under 1 ms exposure per frame, enabling 2D or 3D mapping without pre-or post-processing of the image.

Changes in absorption and refractive index caused by absorption of laser light in the layer semiconductor GaSe (" dynamic" nonlinearities which may lead to optical bistability) are attractive for use in all-optical signal processing application. Nonlinear effects may be very large due to the resonant enhancement near the s h a r p band edge /l/. The binding energy of direct excitons in GaSe is 20 meV /2/, and relatively strong excitonic behaviour is observed even a t room temperature /l/. The excitonic absorption resonance saturation causes nonlinear refraction which may be used in optical bistable devices /3/.In this note we present the results of picosecond time-resolved excite-andprobe transmission measurements at the absorption edge of GaSe a t room temperature. Self-screening of resonantly excited excitons and the screening of excitons by free c a r r i e r s were observed.The measurements were made on the ultrashort-time spectrometer described elsewhere /4/. A 7 ps single pulse of the mode-locked Nd phosphate glass l a s e r was f i r s t selected, amplified, and then converted to the second harmonic a t 527 nm used for band-to-band excitation and to the picosecond supercontinuum used as a probe pulse. The second harmonic radiation could be converted to the pulses of the stimulated Raman scattering in ethanol (622 nm) enabling the resonant excitation of excitons in GaSe. The probe beam was split into one passing through the sample and another serving a s a reference. The spectra of both these pulses were recorded simultaneously employing a polychromator coupled with the optical multichannel analyser OMA-2.Time-resolved transmission measurements within the time range of about 700 ps were performed with a time resolution of 7 p s using a variable time 1) Hausvogteiplatz 5 -7, DDR-1086 Berlin, GDR.

No abstract

The scintilator detectors are sensitive to both neutron and gamma radiation. Therefore, right identification of the pulses which generated by neutrons or gamma ray from these detectors plays an important role in neutron measurement by using scintilator detector. In order to improve the ability to pulse shape discrimination (PSD), many PSD techniques have been studied, developed and applied. In this work, we use a basic configuration of a Fully connected Neural network (Fc- Net) where the number of elements of the network is minimum, and each element corresponds to identified specification of neutron or gamma pulses measured by using EJ-301 scintilator detector. The minimum of error principle has been applied for neuron network design; therefore, the accuracy of recognitions did not affect by this reduced network. The obtained results show that the identify accuracy of FcNet is higher than those of digital charge integration (DCI) method. Being tested using 60Co radioactive source, it is shown that, with the application of the FcNet, the accuracy of the gamma pulses discrimination acquires 98.60% in the energy region from 50 to 2000 keV electron equivalent energy (keVee), and 95.59% in the energy region from 50 to 150 keVee. In general, the obtained results indicate that the artificial neural network method can be applied to build neutron/gamma spectrometers with limited hardware.