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PURPOSE To present an x-ray tube system capable of in vitro ultrahigh dose-rate (UHDR) irradiation of small

The physical porosity ${\Phi}$Φ of a porous material determines most of its properties. Although the optical porosity ${\Phi} _{\textrm {opt}}$Φopt can be measured, relating this quantity to ${\Phi}$Φ remains a challenge. Here we derive relationships between the optical porosity, the effective refractive index $n_{\textrm {eff}}$neff and the physical porosity of weakly absorbing porous media. It introduces the absorption enhancement parameter ${B}$B, which quantifies the asymmetry of photon path lengths between the solid material and the pores and can be derived from the absorption coefficient $\mu _a$μa of the material. Hence ${\Phi}$Φ can be derived from combined measurements of $n_{\textrm {eff}}$neff and $\mu _a$μa. The theory is validated against laboratory measurements and numerical experiments, thus solving a long-standing issue in optical porosimetry. This suggests that optical measurements can be used to estimate physical porosity with an accuracy better than 10$\%$%.

The development of a novel broadband and tunable optical parametric generator (OPG) is presented. The OPG properties are studied numerically and experimentally in order to optimize the generator’s use in a broadband spectroscopic LIDAR operating in the short and mid-infrared. This paper discusses trade-offs to be made on the properties of the pump, crystal, and seeding signal in order to optimize the pulse spectral density and divergence while enabling energy scaling. A seed with a large spectral bandwidth is shown to enhance the pulse-to-pulse stability and optimize the pulse spectral density. A numerical model shows excellent agreement with output power measurements; the model predicts that a pump having a large number of longitudinal modes improves conversion efficiency and pulse stability.

Recent advances in the INO broadband SWIR/MWIR spectroscopic lidar will be presented. The system is designed for the detection of gaseous pollutants via active infrared differential optical absorption spectroscopy (DOAS). Two distinctive features are a sub-nanosecond PPMgO:LN OPG capable of generating broadband (10 to

A SWIR/MWIR spectroscopic lidar is proposed for standoff bio-agent cloud detection using simultaneous broadband differential scattering (DISC). Measurements and/or modeling of DISC spectra of simulants are revisited and the rational of the SWIR/MWIR DISC approach is explained, especially in light of the LWIR DISC experiments and conclusions done elsewhere. Preliminary results on the construction of a low power non-linear broadband source in the SWIR/MWIR are presented. Light from a 1064-nm pump laser is passed through a period and temperature tunable PPMgO:LN Optical Parametric Generator (OPG) to generate broadband light with a full width at half maximum (FWHM) of 10 to >100 nm in the SWIR/MWIR between 1.5 and 3.9 μm. Broadband coherent light from this source is to be emitted towards a cloud that generates back-scattering. This source is being used in a short-range chemical remote detection breadboard, showing the possible dual use of the setup. Light collected by the receiver telescope is coupled to a grating spectrometer and the return signal (DISC in the proposed setup) is detected using a gated MCT-APD array in much the same way clouds are interrogated using UV-LIF. A programmable volume of space along the laser beam path is imaged at the entrance of the spectrometer and 320 spectral channels can be measured simultaneously, attenuating the effects of atmospheric instabilities on DISC measurements. Proposed follow-on work will be presented.

We present a new method for measuring the semiconductor optical amplifier (SOA) linewidth enhancement factor, employing a configuration wherein the SOA is placed within a loss modulated fiber ring cavity operated in the FM laser regime. This allows an easy phase-index measurement in lasing operation at small modulation frequencies. A comparison with the conventional FM/AM technique enables independent measurement of the two underlying phase modulation mechanisms: thermal effects from the current modulation and gain-to-refractive index coupling.

We present methods for controlling both laser linewidth and lineshape via FM laser operation for tunable single frequency oscillated SOA-based fiber ring lasers, using either phase modulation, or amplitude modulation, or current modulation of SOA.

This work presents the proof of concept of a remote sensing system designed for the detection of molecular species such as gas pollutants via active differential optical absorption spectroscopy in the short- and mid-wavelength infrared. The system includes an optical parametric generator generating broad linewidth pulses tunable between 1.5 and 3.8 μm. A telescope coupled to a grating spectrograph and an in-house gated HgCdTe avalanche photodiode measures the whole return spectrum from each pulse. Experiments show simultaneous detection in atmospheric air and inside a cell of H2O and CO2 at 2 μm, and H2O and CH4 at 3.3 μm. The detection limits for CO2 and CH4 are 158 and 1 ppm·m, respectively. A new algorithm is also presented enabling the determination of concentrations when spectra include strong absorption features.

We report how the linewidth and line shape of a tunable semiconductor-optical-amplifier-based fiber ring laser can be actively adjusted by applying an intracavity frequency modulation to the laser. Frequency-modulated laser operation is achieved by driving the phase modulator frequency close to the cavity axial-mode spacing, leading to a constant-amplitude laser output having a periodically varying instantaneous frequency. The resulting linewidth varies proportionally with the inverse of the frequency detuning, and it is adjustable from submegahertz to over more than 5 GHz. By appropriate selection of the modulating waveform we have synthesized a near-Gaussian output line shape; other line shapes can be produced by modifying the modulating waveform. Experimental observations are in good agreement with a simple model.