We demonstrate shockwave-induced nucleation and crystallization in supersaturated aqueous KNO3 using a single 7 ns, 532 nm laser pulse on a metallic substrate. The pulse launches shockwaves at low peak power densities (2.18-2.73 GW/cm2), triggering rapid synchronized nucleation. Crystal morphology and changes in length and width were monitored as a function of time. Crystal dimensions increased linearly with time, with enhanced longitudinal growth yielding anisotropic, needle-like morphologies. At fixed power density, longitudinal growth scaled linearly with concentration, whereas lateral growth was suppressed near the spontaneouscrystallization threshold. Nearly constant growth rates indicate interface-limited kinetics and yield narrow, Gaussian-like size distributions.

The performance of a blue-emitting external-cavity diode laser (ECDL) incorporating a commercial gallium nitride (GaN) Fabry–Perot laser diode was systematically investigated with respect to diffraction grating type, groove density, and polarization orientation using the Littrow configuration. Holographic and ruled gratings of varying resolutions were examined in both parallel and perpendicular orientations. Our results demonstrate that a holographic grating with 1800 grooves/mm in the parallel orientation yields optimal performance: a maximum output power of 37.5 mW, slope efficiency of 0.35 W/A, and a narrow spectral bandwidth of 20 pm (limited by spectrometer resolution). The system achieved a single-mode wavelength tuning range up to 4.1 nm, a side-mode suppression ratio (SMSR) of 37 dB at 445 nm, and stable operation with output power fluctuation limited to just 0.4

In this study, single-shot laser-induced crystallization was employed to trigger nucleation and accelerate crystal growth in supersaturated KNO3 solutions. Time-resolved observations of crystallization, initiated by 7-ns, 532-nm laser pulses at peak power densities of 85.7–107 GW cm−2, are presented. A theoretical framework for single-pulse nucleation and early crystal growth in metastable solutions is also developed to interpret the observed dynamics. Post-growth analysis of harvested crystals was performed to monitor the evolution of crystal size, morphology, and size distribution over time scales ranging from seconds to a few minutes. This short timescale, relative to spontaneous crystallization, allows for single-shot crystallization studies that are unaffected by spontaneous nucleation. Average crystal dimensions were found to increase linearly with laser power density, with longitudinal growth rates exceeding lateral growth, which resulted in the production of needle-like crystals. Smaller, slower-growing crystals were produced by lower-intensity pulse irradiation. Longitudinal growth rates were observed to rise linearly with solution concentration, while lateral growth peaked at S = 1.2 and declined at S = 1.3, indicating the dominance of longitudinal growth at higher concentrations nearing the threshold for spontaneous crystallization initiation. Crystal size distributions were narrow and well-described by Gaussian fits, suggesting temporally synchronized nucleation and a uniform growth environment.

The influence of the grating type (holographic or ruled), resolution, and polarization on the performance of an external cavity diode laser (ECDL) emitting in the blue spectral region are investigated. The single mode ECDL is designed in Littrow configuration and uses an uncoated low-power GaN Fabry-Perot (FP) laser diode, which forms the gain medium. The emitted Fabry-Perot laser diode beam, which is TE-polarized in the plane of the p-n junction, after collimation, is directed incident on the grating. The frequency-selective element, which is used for longitudinal mode selection, is placed outside the FP laser diode cavity to form the extended cavity laser diode. The first-order diffraction is reflected directly into the FP laser diode, while the zero-order is the output from the ECDL. The preliminary results about slope efficiency, output power, power stability, tuning range, and linewidth of the blue ECDL using different gratings with different resolutions and orientations are shown.

The basic characteristics and performance of a detection chain for a LIDAR system used in remote sensing of the atmosphere are presented. The detection chain allows high spatial and temporal resolution, reliable operation, and a wide dynamic range. The achieved noise equivalent power (NEP), signal-to-noise ratio (SNR), and detection limit are presented. The detection chain is characterized by its low power requirements, low cost, easy use, and flexibility.

This study investigates water escape and invasion dynamics in commercial alumina discs, which have sharp size distributions and average pore sizes of 50, 80, and 150 nm, using two different methods, namely, gravimetric and Gas in Scattering Media Absorption Spectroscopy (GASMAS). Before performing measurements in ambient air, the samples were initially placed in a water-saturated environment for the escape study, while for the invasion study, they were initially put in a vacuum environment. Both methods were found to agree and revealed that the time constants for escape and invasion processes were inversely proportional to the average pore sizes. However, the GASMAS method has the capability of distinguishing between water vapor and liquid content in the samples and assessing them simultaneously.

A single-mode external cavity diode laser (ECDL) emitting in the blue spectral region is developed. The ECDL, which uses a low-power Fabry-Perot laser diode, is designed in the Littrow configuration using a reflective holographic grating. The ECDL has a narrowband emission at 448 nm of 0.01 nm that coincides with a strong absorption cross-section of NO2 gas molecule, tuning ranges of 4.0 nm just above the threshold and 0.2 nm at high injection current. A maximum output power of 60 mW and an efficiency of 80 % with respect to the Fabry-Perot laser diode in free-running condition are achieved. High stability of the laser system over many hours was also achieved with a fluctuation of less than 1 %.

The high-resolution emission spectra of a GaN-based semiconductor laser were utilized to investigate the external differential quantum efficiency variation with temperature and stability over an extended period of continuous operation time. Moreover, the dynamics and evolution of the optical gain and longitudinal modes emitted both below and above threshold current were also reported. Upon studying the L-I curves over the full range of operating current and temperature, three distinct temperature regimes of the quantum efficiency were identified, with the regime of the temperature range 285–301 K yielding the highest stability. The thermal stability of the laser was also assessed by monitoring the variation of threshold current with temperature.

An external cavity diode laser (ECDL) in Littrow configuration with narrowband emission at 448 nm is presented. This wavelength coincides with a strong absorption cross-section line of the NO2 gas molecule in the blue spectral region. The ECDL is based on a commercially available multi-longitudinal modes GaN Fabry-Perot laser diode. Longitudinal mode selection is performed using a reflective holographic grating. The Littrow angle is fixed at 43.2 deg relative to the laser diode axis and the diffraction grating is at 3 cm from its output facet. Maximum tuning range of 3.8 nm is achieved with a linewidth of about 0.01 nm at the rated current. The lowest linewidth is obtained with the grating lines oriented parallel to the plane of the p-n junction of the laser diode. The slope efficiency of the ECDL is 0.35 (mW/mA), which is 30% lower than that of the laser diode. The maximum output power achieved by the ECDL is about 40 mW, which is about 75% of that of the laser diode. Maximum power efficiency is also obtained with the polarization direction of the laser diode parallel to the grating grooves. An excellent power stability is achieved over 2 h of continuous operation, with <1% fluctuation.

We investigate non-equilibrium states created by a laser beam incident on a superconducting NbTiN filament subject to an electrical pulse at 4 K. In absence of the laser excitation, when the amplitude of the current pulse applied to the filament exceeds the critical current value, we monitored the delay time $t_{d}$ that marks the collapse of the superconducting phase which is then followed by a voltage rise. We linked the delay time to the applied current using the time-dependent Ginzburg-Landau (TDGL) theory, which enabled us to deduce the cooling (or heat-removal ) time from the fit to the experimental data. Subsequently, we exposed the filament biased with a current pulse close to its critical value to a focused laser beam, inducing a normal state in the impact region of the laser beam. We showed that the energy of the incident beam and the incurred delay time are related to each other by a simple expression, that enables direct measurement of incident beam energy by temporal monitoring of the transport response. This method can be extended for usage in single-photon detection regime, and be used for accurate calibration of an arbitrary light source.

In this paper, an external cavity diode laser (ECDL) in Littrow configuration with narrowband emission is presented. The laser system is based on a commercially available GaN Fabry-Perot laser diode. Longitudinal mode selection is performed using a reflective holographic grating. Tuning range over 3.4 nm is achieved with a short linewidth of 0.02 nm at the rated current. The ECDL system is integrated into an optical sensor for remote detection of Nitrogen Dioxide (NO2) gas.

In this study, a newly developed setup based on laser-induced shockwave crystallization coupled with electric conductivity monitoring was employed to study the growth of crystals in supersaturated solutions and to investigate possible clustering in undersaturated solutions of potassium nitrate (KNO3). A comparison was drawn between crystals induced by laser irradiation, by shockwaves, and spontaneously in terms of crystals' mean size, shape, and size distribution. The size distribution of produced crystals by shockwaves was also characterized in terms of laser irradiation time. The results show that produced crystals by shockwaves propagation have the sharpest size distribution and the smallest mean dimensions compared to crystals grown spontaneously or by direct laser induction. Real-time monitoring of nucleation was also performed in supersaturated solutions, while decrease in conductivity was observed in undersaturated solutions as a function of laser irradiation time.

This paper describes a ground-based pulsed Cloud-Aerosol Lidar system for providing a backscatter laser signal at both wavelengths 532 and 1064 nm, from which aerosol and cloud profiles are derived. The Lidar system is installed on the roof of a building in a monostatic biaxial configuration. Test measurements show that the Lidar system is capable of resolving cloud structure and identifying the presence of aerosols from the ground up to a distance of 15 km. The performance of the Lidar system is considered adequate for routine measurements. This paper provides information on the basic features and performance of the Lidar system. The measurements confirm the excellent sensitivity of the detection chain. Recent improvements in the Lidar detection chain with improved dynamic range are also discussed.

GAs in Scattering Media Absorption Spectroscopy (GASMAS) is used to correlate the average pore size within mesoporous alumina samples to the broadening of the absorption lines of oxygen gas and water vapor entrapped within the pores. Collisions of gas molecules cause extra broadening to the absorption linewidths if the average time between collisions is smaller than the inverse of the linewidth of the absorption line. A gas molecule can collide either with another molecule or with the walls of its container. Hence, for a gas entrapped within a porous medium that has an average pore size comparable to the mean free path of intermolecular collisions, collisions of the gas molecules with the walls of the pores can cause extra broadening. This extra broadening is used to estimate the average size of the pores. At atmospheric pressure, the mean free path of intermolecular collision is about 100 nm and thus broadening due to collision with the walls of the pores should be noticeable for pore sizes of order of 100 nm or less. In this work, high resolution tunable singlemode diode lasers at 761 nm and 936 nm are employed to study the absorption from oxygen gas and water vapor, respectively. The samples used are made from porous pure 𝛼-alumina with average pore sizes ranging from 50 to 150 nm.

A new spectroscopic method using a multimode tunable blue diode laser and direct absorption spectroscopy is developed to detect trace amount of nitrogen dioxide (NO 2 ) gas. The method produces distinctive signatures for NO 2 absorption that are utilized to accurately measure the gas concentration. The NO 2 signatures are obtained by measuring the transmission through a calibrated NO 2 gas sample as a function of laser injection current at a fixed laser temperature. These transmission curves are also calculated from the NO 2 absorption cross section and laser emission spectra. The measured and calculated transmission curves are found to agree reasonably well within 5%. In this study, two different blue diode lasers emitting around 445 nm are investigated. For both lasers, a detection limit of about 0.1 ppm can be achieved in a 40-cm long gas cell under standard atmospheric conditions.

A digital counting and display circuit for long distance laser rangefinder is presented. The laser rangefinder uses a pulsed Nd:YAG laser emitting in the near-infrared spectral region at the wavelength of 1.06 micrometer to measure distances to targets with a resolution of 5 m, an accuracy of +/- 1.5 m, and a maximum range of 15 km based on a direct time-of-flight method. The detection is achieved with a probability of detection of 0.99 and a probability of false alarm of 1.5X10-7. The digital circuit is characterized by its simplicity, versatility and reliability. It is placed at the end of an optoelectronic detection chain formed by a silicon avalanche photodiode, a low-noise and fast multistage amplifier, and a fast analog-to-digital converter.

Here, we investigate effects of the size of pores in porous alumina powders on the broadening of the oxygen gas absorption line. The line broadening is caused by collisions of oxygen molecules with the pore walls and is extracted using gas in scattering media absorption spectroscopy (GASMAS), while the average pore size is determined using the gas adsorption technique. The average pore size of the samples studied lies within the range 10-40 nm. In this range, the contribution of the wall collision broadening is found to be approximately inversely related to the average pore diameter. Furthermore, the confined oxygen gas absorbance measured by GASMAS is found to be linearly correlated with the effective porosity evaluated by the saturation method.