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Polarimetric imaging cameras require polarimetric calibration to accurately estimate the incident Stokes vector of incoming radiation. This calibration establishes a relationship between changes in the sensor signal and incident Stokes vector. In the standard procedure, an imager is presented with a set of input Stokes vectors with two different radiance values. In the long-wavelength infrared (LWIR) and mid-wavelength infrared bands, blackbodies with different temperatures are used for each set of Stokes vectors. The radiometric offset is subtracted, and standard radiometric or nonuniformity correction procedures are performed in a separate step. This paper proposes an alternative all-in-one approach that combines radiometric calibration, nonuniformity correction, and polarimetric calibration. The standard and proposed methods are compared for a division-of-time LWIR polarimeter. The proposed calibration method achieves an RMS error of 0.34% compared with the conventional technique's error of 0.83%, yielding a factor of 2.4 improvement in the reconstructed accuracy of a linear Stokes vector; in addition, it is less time-consuming and less prone to ambient temperature fluctuations than the typical two-point method. The method also accounts for beam wander and narcissus effects and enables simple, straightforward polarimetric measurement.

A procedure for simulating the Mueller matrix of an optical system across the field of view of a long-wavelength infrared (LWIR) imaging polarimeter is presented in this paper. The procedure is based on a ray-tracing model and uses off-the-shelf software and custom add-on procedures written in MATLAB. A simulation was conducted to obtain polarization ray tracing across the entire surface of the focal-plane array for a set of wavelengths within the LWIR (8-14 µm) window and within the instrument's field of view of 7.3 ∘ ×5.5 ∘ with a set of different starting polarization states. Finally, the simulation results are compared with measurement data obtained from the home-designed optical train of a polarimetric camera. For Mueller matrix entries significantly larger than zero, both simulation and experiment results show high consistency, with overall RMS error of less than 2%. The presented results are useful when anticipation of a Mueller matrix of an imaging polarimeter is of high importance.

We report on the method of signal processing in a passive long-wave infrared (LWIR) image polarimetric sensor. The method enables the detection of natural and manmade targets. It includes the error related to the rotation of the polarizing element during an image reading as well as permits the polarimeter operation without a classical phase synchronization loop. In addition, to verify the proposed method, a prototype of a time-division polarimetric system that operates in the 8-12 µm band and is based on an uncooled microbolometric detector array was designed and developed. The entire system enabled us to successfully detect a few types of artificial objects from the distance of several tens of meters. The maximum image refresh rate was 5.45 Hz and could be further increased.

Broadband, mid-infrared supercontinuum generation in a step-index fluoroindate fibre is reported. By using ~70-picosecond laser pulses at 2.02 μm, provided by an optical parametric generator, a wide spectrum with a cut-off wavelength at 5.25 μm and a 5-dB bandwidth covering the entire 2-5 μm spectral interval has been demonstrated for the first time. The behaviour of the supercontinuum was investigated by changing the peak power and the wavelength of the pump pulses. This allowed the optimal pumping conditions to be determined for the nonlinear medium that was used. The optical damage threshold for the fluoroindate fibre was experimentally found to be ~200 GW/cm 2 .

We report high-power supercontinuum (SC) generation in a step-index fluorozirconate (ZBLAN) fiber with a zero-dispersion wavelength shifted to ~1.9  μm. Pumping the fluoride fiber with 2.75 W of power provided by a thulium-doped fiber amplifier, a continuous spectrum extending from ~0.85 to 4.2 μm with 2.24 W of average output power was achieved. Over 61% (1.37 W) of the total output power corresponds to wavelengths longer than 3 μm, which shows, to the best of our knowledge, the highest power conversion efficiency toward the mid-IR spectral band in relation to the output spectrum width. A linear SC power scalability up to 5.24 W, with a spectral band of ~0.9-4  μm, with repetition rate and pump power provided by a 1.55 μm fiber master-oscillator power amplifier system, is also demonstrated.

We report on a generation of self-starting mode-locked resembling (MLR) pulses in an all-fiber, gain-switched Tm(3+)-doped fiber laser operating at 2 μm wavelength, which we believe to be the first demonstration of such an approach. The laser delivers 100% modulated MLR pulses within an envelope of ~30 ns gain-switched pulse at a repetition rate of 30 kHz. The maximum average output power is 0.4 W and the maximum peak-power of MLR pulses can be as high as 1.1 kW. The performance of the laser is described.

We demonstrate a novel method of mid-infrared (mid-IR) supercontinuum (SC) generation with the use of a 2 µm gain-switched self-mode-locked thulium-doped fiber laser. SC radiation ranging from ~1.9 to 3.8 µm wavelength, generated in a single-mode ZBLAN fiber with a zero-dispersion wavelength (ZDW) shifted to ~1.9 µm, is reported. An average output power of 0.74 W with 0.27 W at wavelengths longer than 2.4 µm was measured. It is, to the best of our knowledge, the first report on such an approach to generate a mid-IR SC in optical fibers.

A diode-pumped actively Q-switched and actively mode-locked Tm3+-doped double-clad silicate fiber laser is reported providing up to 5 W of average output power at ~60 kHz Q-switch envelope repetition rate and ~8 μJ subpulses with up to 2.4 kW peak power. Using this source as a pump laser for supercontinuum generation in a ZBLAN fiber, over 1080 mW of supercontinuum from 1.9 μm to beyond 3.6 μm was obtained at an overall efficiency of 3.3% with respect to the diode pump power.

This paper presents a computer simulation of reflected and scattered laser radiation for calculating the angle of laser shields performed with the Laser Shield Solver computer program. The authors describe a method of calculating the shield angle for laser shields which protect workers against reflected and scattered laser radiation and which are made from different materials. The main assumptions of the program, which calculates and simulates reflected laser radiation from any material and which can be used for designing shield angles, are presented. Calculations are compared with measurements of reflected laser radiation. The results for one type of laser and different materials which interacted with a laser beam showed that the Laser Shield Solver was an appropriate tool for designing laser shields and its simulations of reflected laser radiation distribution have practical use.

An actively Q-switched Er:YAG laser generating pulses at 2.94 microm has been developed and investigated. For a single Er:YAG generator at 3 Hz repetition rate, pulses of 91.2 ns duration and 137 mJ energy have been obtained. It corresponds to pulse train with high-peak power of ~ 1.5 MW. For 10 Hz repetition rate 30 mJ of output energy in single pulse has been achieved. These results, according to our knowledge, are the best world-wide achievements.