This paper investigates the nonlinear propagation dynamics of finite Airy-Gaussian (AiG) laser beams in a uniform dense collisionless plasma using the Wentzel-Kramers-Brillouin (WKB) and paraxial ray approximations. Instead of treating the coupled beam width parameter differential equations (BWPDEs) solely as evolution equations, the beam propagation is analysed within an equivalent classical dynamical framework. The beam width evolution is reformulated as a two-dimensional dynamical system governed by propagational quasi-Hamiltonian functional and an effective pseudo-potential. An energy-like propagational quasi-Hamiltonian functional is derived characterizes the nonlinear beam dynamics. The evolution of the system is further interpreted through kinetic energy-like and effective pseudo-potential terms. The analysis reveals that, the quasi-Hamiltonian functional governs the self-trapping, oscillatory self-focusing and defocusing behavior of the beam. Different propagation regimes are identified according to the evolution of the quasi-Hamiltonian functional; near-zero values correspond to self-trapping, bounded oscillations indicate stable propagation and divergent behaviour signifies beam defocusing. The condition for self-trapping, self-focusing, defocusing and beam stability are further examined through a Hessian matrix analysis. The proposed framework provides deeper physical insights into the nonlinear dynamics of finite AiG beams and extends the conventional beam width parameter approach by revealing the underlying dynamical structure of beam propagation in plasma.
With the exponential growth of digital communication channels, the transmission and storage of high-dimensional multimedia data, including images and videos, have become crucial to modern information systems. The areas like defense, healthcare and banking utilize the modern communication channels very often to share information. Thus, ensuring the confidentiality, integrity, and authenticity of sensitive visual information has become a critical challenge. Although there are various conventional data security algorithms that exist, they often encounter limitations in handling large-scale image data due to high computational complexity and slow processing speed. Optical cryptosystems have emerged as a promising alternative owing to their inherent parallelism, multidimensional processing capability, large key space, and high-speed implementation. In this review, recent advancements in optical cryptosystems beyond classical DRPE scheme are summarized. Particularly, we examine the asymmetric optical cryptosystems based on PTFT, QZ decomposition, QZ synthesis, SVD, GSVD, interference, and computer-generated holography. Moreover, this review also discussed the emerging approaches of optical data security using structured light beams such as vector vortex beams. Finally, the review covered various techniques to test the vulnerabilities of optical cryptosystems such as plaintext and modified plaintext attacks, AI based cryptographic attacks, and iterative attacks designed for asymmetric cryptosystems. The objective of this review article is to serve as a reference text for readers from a variety of research backgrounds interested in the domain of optical information security.
Atomic vapor laser isotope separation (AVLIS) of gadolinium has historically emphasized enrichment of the odd isotopes, with external magnetic fields treated primarily as a source of selectivity degradation. Here we revisit polarization-selective photoionization of gadolinium with a different objective: to exploit controlled B-field–induced mixing as a design parameter for enhancing the photoionization of even isotopes. Using density-matrix simulations of a J = 2 → 2 → 1 → 0 excitation ladder, we examine the combined effects of magnetic-field orientation and amplitude, laser polarization, and laser fluence on the photoionization efficiency of 160Gd and 152Gd. We identify operating regimes in which modest magnetic fields (≈10–20 G), appropriately oriented relative to the laser fields, substantially increase even-isotope photoionization probability without catastrophic loss of selectivity. When translated into separation metrics, these conditions yield high theoretical product assays and isotopic cuts approaching or exceeding 60–70
Spatially resolved, quantitative laser diagnostics are needed to understand high-temperature and high-speed flow fields. To that end, a spectrally resolved laser-induced fluorescence diagnostic targeting nitric oxide (in bath gases of Ar and N2) was developed and validated in a series of static cell and shock tube experiments. Also, a spectrally resolved fluorescence model was created to simulate the underlying processes of diatomic spectrally resolved fluorescence and quantify the maximum theoretical measurement rate under various conditions. The diagnostic was validated from 295–1350 K and 2.1–47.0 kPa, and validation experiments showed good agreement with known values—a 3.0
Precise measurement of micro-curvature enables early detection of issues before they reach critical levels, facilitating preventive maintenance and mitigating the risk of significant economic losses and safety hazards. In this paper, we proposed and experimentally demonstrated an innovative sensor for dual parametric simultaneous measurement based on Sagnac-interferometer (SI) constructed by double-clad polarization-maintaining fiber (DPMF). The sensor is designed using a 2 × 2 coupler to connect the DPMF, forming an optical fiber loop structure while granted with a Fiber Bragg granting (FBG). The experiment proves that the SI exhibits curvature sensitivity of − 89.1 nm/m−1 from 0.062 to 0.176 m−1 and − 179.09 nm/m−1 from 0.186 to − 0.26 m−1 while temperature sensitivity of − 1.65 nm/°C. By adding FBG to realize dual parametric simultaneous measurement. The FBG has showed sensitivities of curvature and temperature are − 6.97 nm/m−1 and 0.009 nm/°C. The coefficient matrix approach is employed to simultaneously measure both curvature and temperature. The sensor exhibits ultra-high curvature resolution of 1.1 × 10−4 m−1 and achieves dual-parameter simultaneous measurement for curvature and temperature through a simple fabrication process. Its characteristics of high sensitivity and resolution, low production costs, and straightforward manufacturing make its application prospects in industrial manufacturing and aerospace fields broader.
We demonstrate continuous-wave laser operation of a terbium (Tb3+)-doped ZBLAN fiber emitting in the green spectral region. Under pumping at 486 nm, laser oscillation at 542 nm was achieved in a 4 m long Tb3+:ZBLAN double-clad fiber. A maximum output power of 6.2 mW was obtained with a slope efficiency of 1.2
I designed and experimentally performed digital holographic microscopy (DHM) in which a halogen lamp is used as a light source and theoretical two-point resolution is submicron. The DHM system consists of a commercially available optical microscope and a common-path self-reference in-line digital holography system. Quantitative phase imaging of a three-dimensional (3D) object is performed without speckle noise. 3D imaging of an object containing submicron apertures is performed with temporally incoherent thermal light.
Diabetes mellitus (DM) is a group of metabolic diseases characterized by chronic hyperglycemia, which develops due to insulin resistance (T2DM), insulin deficiency, or glucagon overproduction (T1DM). One of the key consequences of hyperglycemia is nonenzymatic glycation of biomolecules, including proteins, lipoproteins, and lipids. The aim of this study was to determine the optical properties of adipose tissue in healthy rats and rats with experimentally induced T1DM using multiwavelength refractometry and spectroscopy, followed by data verification through histological analysis and molecular modeling. Glycation of collagen and phosphatidylethanolamine was shown to lead to expansion and destabilization of their hydration shells. A comprehensive analysis revealed a correlation between optical properties, structural changes in tissues, and their hydration. The differences in the optical properties of abdominal fat, arising from pathological glycation and hydration, could enable the development of label-free optical methods to monitor T1DM in experimental settings. This approach may ultimately support new strategies for predicting, diagnosing, and tracking the progression of T1DM in humans.
We present the first step towards an intelligent thin-disk multi-pass amplifier (I-TDMPA), by simulatively proving the ability of a neural network (NN) for the detection of misalignment. A digital twin of one of our experimental systems was implemented using a specifically developed ray tracing simulation. The digital twin was used to generate more than 200,000 sets of training data to train a neural network (NN) with the goal to be able to determine misalignment of the many optical elements of a multi-pass amplifier in a simulation model, solely by observing the beam. The predictions of the NN agree very well with the simulated misalignments, which confirms the suitability of artificial-intelligence methods to ensure a safe and stable operation of complex optical systems.
Temperature dependence of the optical path difference in optically transparent materials is governed by both thermal expansion and thermo-optic effects. Combining both effects with a single parameter, referred to as effective thermal expansion coefficient (αeff), which measures change in optical path length with temperature. This quantity, αeff, is important for quantitative characterization of the impact of temperature variations as well as thermal effects on the optical components. This work demonstrates the use of a spectral domain low coherence interferometer (SDLCI) in common path configuration, along with phase sensitive analysis, to measure effective thermal expansion coefficient of fused silica and sapphire samples with sub-nanometer scale optical path length sensitivity. The phase based optical path length retrieval methodology is first established with simulated data and then validated experimentally. Experiments were performed for phase sensitive optical path difference measurements with sub nanometer scale repeatability in using 840 nm wavelength in the temperature range of 35–70 ºC. The experimentally measured values of αeff of fused silica and sapphire samples are found to be in agreement with the values reported in literature.
The quintic nonlinear response of fused silica was investigated using a modified z-scan technique and a cubic-quintic propagation model at femtosecond pulse intensities up to 10 TW/cm^2 . A statistically significant deviation from the purely cubic Kerr response was observed only at the highest intensities. Interpreting this deviation within the perturbative cubic-quintic model yields effective quintic nonlinear refractive indices n_4=-(4...7)· 10^-6 cm^4/TW^2 at a wavelength of 1033 nm and n_4=-(8...16)· 10^-6 cm^4/TW^2 at 517 nm. Since plasma-induced refractive effects may contribute to the observed higher-order response, these values should be regarded as the upper bounds of the negative quintic nonlinear refractive index of fused silica. The obtained bounds are approximately 1–2 orders of magnitude lower than the previously reported values.
Single-pixel imaging (SPI) reconstructs an object’s image via computational methods using a single-point photodetector and a sequence of mask patterns. A fundamental trade-off exists in SPI between the sampling rate and the fidelity of the reconstructed image: while increasing the number of patterns enhances image quality, it simultaneously scales the volume of the measured light intensity data. In this study, we propose a SPI data compression based on audio compression technology, taking advantage of the fact that light intensity data is inherently one-dimensional. Our results demonstrate that the Free Lossless Audio Codec algorithm achieves significantly higher compression ratios than conventional lossless methods based on LZ77 and Huffman coding, without compromising image quality. Furthermore, we show that lossy formats such as MP3 and Ogg Vorbis can achieve even higher compression ratios, albeit with minor degradation in the final reconstruction.
Galvanometric scanners (galvo-mirrors, GMs) are key beam-steering elements in laser scanning microscopy, where their dynamic performance directly limits imaging speed, precision and field fidelity. In practical microscopy systems, scanner behaviour is governed by dynamic parameters such as settling time, frequency response and phase delay, that critically influence image quality, particularly at high scanning rates. Here, we present a comparative characterization of two GM systems integrated into custom-built laser scanning microscopy platforms. Rather than evaluating standalone scanner units, both systems were examined as fully assembled components within operational microscopes, allowing combined effects of mirror inertia, driver electronics and feedback control to be assessed. Under identical driving conditions, scanner dynamics were quantified through measurements of step response, amplitude and waveform fidelity and frequency-dependent phase delay. These measurements were complimented by representative imaging examples that directly link scanner dynamics to observable image distortions. The results show that the first GM system exhibits faster step response, smaller phase delay and improved amplitude retention across the operational frequency range of 200–800 Hz, indicating higher dynamic bandwidth. In contrast, the second GM system demonstrates slower response and stronger amplitude attenuation at higher frequencies, leading to reduced usable field of view, geometric distortions and larger phase delay leading to misregistration between forward and backward scans. This study provides practical guidance for selecting and optimizing galvanometric scanners and scan parameters in high-performance laser scanning microscopy.
The implementation and characterization of green external cavity diode lasers (ECDL) in Littrow configuration is presented. It is specifically developed for Raman spectroscopy. Eight distinct green laser diodes are systematically characterized and compared: six broad-area diodes and two transverse single-mode diodes. All diodes achieve wide tuning ranges between 8 nm and 12 nm and output powers of more than 100 mW. One of the transverse single-mode diodes reached 45 mW maximum output power, which is sufficient for Raman measurements. Preliminary Raman measurements using a broad-area diode laser demonstrate the feasibility of this ECDL setup for spectroscopic applications.
Photopatternable hydrogels with controllable refractive index (RI) have gained increasing attention as a tool for biophotonic calibration, optical phantoms, and studies of light–matter interaction in soft matter. Here, we investigate UV-induced photopolymerization in gelatin-methacrylamide (MAM) hydrogels as a low-toxicity, optically transparent platform enabling spatial RI modulation. The hydrogels were synthesized using non- or low-toxic components and characterized by fiber-optic refractometry, validated against an Abbe refractometer with deviations below 1
Entomological photonic sensors enable continuous, automated and non-invasive monitoring of flying insects by recording optical signals of insects transiting in their field-of-view. These instruments can observe extremely large numbers of insects and provide ecological measurements such as aerial density [insect/m3] and biomass density [mg/m3] with temporal resolution down to a minute and minimal downtime. Nevertheless, their taxonomic resolution is limited; since deriving reliable taxonomic signatures from optical signals is difficult, knowing insects represent the most species-rich group of organisms. In this study, we focus on the influence of body orientation during transit, a factor that directly impacts how the body and wings contribute to the recorded signal. Using numerical simulations based on a 3D model of an Apis mellifera (honeybee), and laboratory experiments with Musca domestica (housefly), we analyze extinction signals using Mel-Frequency Cepstral Coefficients. They characterize the time-frequency structure of the waveform, caused by changes in orientation of an insect as it crosses the beam. A Gaussian Process regression model trained on these coefficients predicts symmetry-reduced orientation angles with high accuracy. By correcting for orientation, we can retrieve a more accurate estimate of the insect's body optical cross-section. This correction may lead to improved identification and mass estimation. Our simulation results show that orientation effects can alter apparent cross-sections by up to 83% in this particular case, however this may be even more pronounced for insects with elongated bodies, underscoring the importance of accounting for them in biomass calculations obtained from photonic sensors. These findings demonstrate that orientation-sensitive signal analysis can refine predictor variables and improve the reliability of photonic sensors in providing ecological metrics beyond abundance, paving the way toward higher taxonomic resolution.
We propose a simple analytical approach for description of energy transfer from ultra-short laser pulses to quantum oscillator in the thermal equilibrium based on approximate expression for oscillator spectral function. Formulas for the probability of energy transfer in the limits of high and low temperatures are derived and analyzed. The characteristic features of energy transfer to a quantum oscillator from unipolar pulses, wavelets and multi-cycle laser pulses are established.
We develop a diode-pumped cryogenically cooled Yb: KGd(WO4)2 (Yb: KGW) crystal regenerative amplifier (RA). At 77 K, it delivers 1.28 mJ output pulses with 2.9 nm spectral bandwidth and output power stability of 0.7
Antimony selenide (Sb2Se3) is a promising photovoltaic material due to its high absorption coefficient and favorable mobility. However, its long-term stability and defect dynamics remain insufficiently explored. In this study, Sb2Se3 thin films were fabricated via magnetron sputtering, with post-deposition annealing used to induce a transition from an amorphous (Sb-1 film) to a crystalline orthorhombic phase (Sb-2 film). We systematically investigated the impact of ambient air, oxygen, UV irradiation, and light-soaking on the electronic properties of these films. Key findings reveal that oxygen exposure increases dark conductivity (σD) by approximately one order of magnitude, a process largely reversible under vacuum for both phases. In contrast, radiative aging induced divergent responses: while amorphous film showed transient responses, crystalline samples exhibited complex and partially irreversible defect dynamics. Specifically, UV irradiation and long-term atmospheric exposure induced permanent shifts in the mobility-lifetime (mt) product of crystalline film, indicating alterations in dominant recombination pathways. Furthermore, mt products increased during light-soaking, suggesting the activation of metastable states. These results provide critical insights into phase-dependent environmental sensitivity, highlighting that precise crystallinity control and encapsulation are paramount for Sb2Se3 device stability.
In this work, a set of effective semiconductor Maxwell–Bloch equations has been used to study the dynamics of a bound-to-continuum terahertz quantum cascade laser (QCL) under external optical feedback at both threshold and maximum operating currents. The used model is extended to include current-dependent input parameters obtained from density matrix transport simulations, enhancing physical accuracy and enabling device-specific modelling within the relevant current range for a specific fabricated QCL. Near threshold, external feedback shifts the emission from single-mode to multimode and, depending on the external cavity length, can produce different dynamical regimes. The feedback-induced reduction of the threshold current is demonstrated and quantified. At maximum operating current, the laser is inherently multimode, with external feedback producing different dynamical regimes. The model predicts high sensitivity of output power to variations in the external cavity. When operating with a few modes, the output remains interpretable for sensing applications, whereas highly multimode emission leads to noisy, less interpretable signals. This framework provides insight into self-mixing and mode competition phenomena, aiding in the identification of QCL designs that minimise multimode behaviour for reliable THz sensing and has a direct impact on the advancement of QCL-based sensing and communication applications.
