A trace gas sensor based on pulsed cavity ring-down spectroscopy (CRDS) was developed for measurement of the ν4 fundamental vibrational band of ammonia (NH₃) centered at 1468.898 cm⁻¹. A pulsed distributed feedback quantum cascade laser (DFB-QCL) operating at 6.8 µm (1470.58 cm⁻¹) quite well covered the absorption band of the ammonia and strong fundamental vibrational absorption bands of different molecular gases in this unexplored region. The cavity was partially evacuated down to 0.4 Atm by a turbo-molecular pump to reduce the partial interference between the NH₃ spectra and water near the absorption peak of ammonia. A sensitivity of nine parts per billion was reached for a measurement time of 120 s as well as an optical path length of 226 m. The device demonstrated high spectral performance and versatility due to its wide tuning range, narrow linewidth, and comparatively high-energy mid-IR radiation in the relatively unexplored 6.8 µm region, which is very important for high-resolution spectroscopy of a variety of gases.

We report on a laser system based on difference frequency generation (DFG) to produce tunable, narrow-linewidth ( < 30 p m ), and comparatively high-energy mid-IR radiation in the 6.8 µm region. The system exploits a lithium thioindate ( L i I n S 2 ) nonlinear crystal and nanosecond pulses generated by single-frequency Nd:YAG and Cr:forsterite lasers at 1064 and 1262 nm, respectively. Two experimental configurations are used: in the first one, single-pass, the mid-IR energy achieved is 205 µJ. Additional increments, up to 540 µJ, are obtained by performing double-pass through the nonlinear crystal. This laser has been developed for high-resolution photon-hungry spectroscopy in the mid-IR.

We present the design of a Cr:forsterite based single-frequency master-oscillator power-amplifier laser system delivering much higher output energy compared to previous literature reports. The system has four amplifying stages with two-pass configuration each, thus enabling the generation of 24 mJ output energy in the spectral region around 1262 nm. It is demonstrated that the presented Cr:forsterite amplifier preserves high spectral and pulse quality, allowing a straightforward energy scaling. This laser system is a promising tool for tunable nonlinear down-conversion to the mid-infrared spectral range and will be a key building block in a system for high-resolution muonic hydrogen spectroscopy in the 6.8 μm range.

This study investigates the effect of deposition time on the structural, morphological, and optical properties of ZnO thin films synthesized by single-step chemical bath deposition (CBD) without the use of a seed layer. The films were systematically characterized using X-ray diffraction (XRD), scanning electron microscopy (SEM), Fourier-transform infrared spectroscopy (FTIR), and UV-Visible spectroscopy in order to establish correlations between growth conditions and film properties. XRD analysis confirmed that all synthesized films are polycrystalline and crystallize in the hexagonal wurtzite structure, with average lattice parameters of a = 3.247 Å and c = 5.209 Å. The crystallite size increased slightly from 13.27 nm to 14.05 nm with increasing deposition time, indicating improved structural ordering and crystallinity. FTIR spectra verified the presence of characteristic Zn–O vibrational modes together with surface hydroxyl groups and other functional bonds related to the growth process. SEM images revealed a strong dependence of surface morphology on deposition time: ZnO microrods evolved from loosely distributed to more compact and densely packed assemblies as the deposition progressed, confirming enhanced film coverage. Optical measurements highlighted significant modifications in the transparency and band structure of the films. The average optical transmittance in the visible range decreased progressively from 68% to 52% when deposition time was extended from 30 to 120 minutes, reflecting increased film density. Concurrently, the optical band gap narrowed from 3.27 eV to 3.22 eV. These findings demonstrate that single-step CBD provides a reliable and controllable route for synthesizing ZnO thin films with tunable physical properties.

The collection and transport of charges at the electrodes are the main factors limiting the efficiency of organic solar cells. Zinc oxide (ZnO) in nanostructured form helps to overcome this problem by introducing a ZnO buffer layer between the photoanode and the donor material. To achieve this, the ZnO thin film must exhibit good crystallinity, along with good electrical conductivity and high optical transparency in the visible range. The aim of this work is to investigate the effect of precursor sources and precursor concentrations on the structural, morphological, and optical properties of ZnO thin films. Three different precursor sources have been used: zinc acetate, zinc chloride and zinc nitrate. In each deposition solution, the precursor concentration varied from 0.1 M to 0.3 M. The ZnO films were deposited on glass substrates and all the films were annealed at 400°C for 3 hours. The structural, morphological and optical properties of deposited films were investigated using X-ray diffraction (XRD), scanning electron microscopy (SEM), and UV-visible spectroscopy respectively. XRD results showed that, regardless of the precursor source, all the ZnO films are polycrystalline with a hexagonal wurtzite structure. ZnO films obtained from acetate and nitrate sources crystallize preferentially along (002) and the peak intensity increases as the precursor concentration increases. SEM images showed that all the ZnO films are homogeneous, but films deposited from zinc acetate and zinc nitrate looked more compact and smoother than those obtained with zinc chloride which looked porous. UV-visible spectroscopy results revealed that the films transmittance depends both on precursor source and concentration. ZnO thin films deposited from zinc acetate at 0.3M concentration exhibit the best transmittance of 95% due to their smooth and uniform surfaces. The band gap of ZnO obtained from the zinc acetate precursor decreases with increasing solution concentration. It is found to be 3.29 eV, 3.26 eV, and 3.22 eV for concentrations of 0.1 M, 0.2 M, and 0.3 M, respectively. It therefore appears that ZnO films obtained from zinc acetate can be used as an electron transport layer for solar cells as they exhibit the best crystallinity and the highest transmittance.