[en] A multilayer mirror for spectral filtering adapted to ultra-short and multi-PW Ti:Sa laser has been designed, manufactured and characterized. The method used to determine both the reflectivity shape and the coating design leads to global compensation of gain narrowing, saturation and spectral phase. The result is a spectral control on 200 nm range while keeping a flat spectral phase. This kind of filter will enable obtaining 15 fs pulse duration for multi-PW laser systems based on Ti:Sa. (authors)

[en] Handheld laser-induced breakdown spectroscopy (HH LIBS) was used to study the elemental composition of four copper alloys and four aluminum alloys to produce calibration curves. The HH LIBS instrument used is a SciAps Z-500, commercially available, that contains a class-1 solid-state laser with an output wavelength of 1532 nm, a laser energy of 5 mJ/pulse, and a pulse duration of 5 ns. Test samples were solid specimens comprising of copper and aluminum alloys and data were collected from the samples’ surface at three different locations, employing a 12-point-grid pattern for each data set. All three data sets of the spectra were averaged, and the intensity, corrected by subtraction of background, was used to produce the elemental calibration curves. Calibration curves are presented for the matrix elements, copper and aluminum, as well as several minor elements. The surface damage produced by the laser was examined by microscopy. The alloys were tested in air and in a glovebox to evaluate the instrument’s ability to identify the constituents within materials under different environmental conditions. The main objective of using this HH LIBS technology is to determine its capability to fingerprint the presence of certain elements related to subpercent level within materials in real time and in-situ, as a starting point for undertaking future complex material characterization work.

[en] Up to now, laser damage growth on the exit surface of fused silica optics has been mainly considered as exponential, the growth coefficient depending essentially on fluence. From experiments with large beams carried out at 351 nm under nanosecond pulses, a statistical analysis is conducted leading to a refined representation of the growth. The effect of several parameters has been taken into account to describe precisely the growth phenomenon. The two principal parameters proved to be the mean fluence and the size of the damage sites. Nevertheless, contributions of other parameters have been estimated too: the number of neighbors around the damage site, the shot number, etc. From experimental results, a model smoothed on a statistical approach is developed that permits the description of a complete sequence of growth. To evaluate the relevance of the modeling approach, the occluded area estimated from modeling is compared with the ones experimentally measured. For this purpose, numerical growth methods have been developed too. It is shown that the approach outlined is appropriate for a more precise description of the growth. (authors)

[en] We report a tunable single-longitudinal-mode laser based on a wedged Nd:YVO₄ gain medium and a YVO₄ wave-plate. By taking advantage of the natural birefringence of YVO₄ and adopting different cutting methods, a wedged Nd:YVO₄ crystal acts as an ideal polarizer by the alignment sensitivity of the optical resonator, and a YVO₄ crystal is used as a wave-plate by adjusting the temperature. A theoretical analysis of the single- longitudinal-mode operation of such a laser configuration is presented. The wavelength can be continuously tuned by the temperature at approximately 0.025 nm/°C, and the temperature tuning ranges of single-longitudinal-mode operation at pump powers of 1 W and 2 W are from 12 °C to 30 °C and from 11 °C to 26 °C, respectively. The maximum single-longitudinal-mode output power with linear polarization is 762 mW at a pump power of 2.2 W with a slope efficiency of 40%.

[en] This paper presents new structures for OR, NOT, and XOR logic gates based on a two-dimensional photonic crystal. The proposed structures are quite linear and have the same basic structure for all three gates. Isolation between input ports is one of the features that is given special attention in this study. The proposed designs reduce the leakage signal from an input port to another input port to less than 17%. The reflection to the input port is less than 30% in the worst case. The structures are designed and simulated, and then their characteristics are compared to previous works. The simulation results show that the proposed structures, despite being linear, have a smaller size, faster response time, and acceptable contrast ratio in comparison to those of the other works. The results of the tolerance study demonstrate that manufacturing tolerance must be less than 5% for the proposed gates’ working properly.

[en] Transverse mode-locking in an end-pumped solid state laser by amplitude modulation with an acousto-optic modulator was investigated. Using the stochastic parallel gradient descent algorithm the modal power coefficients and the modal phases of the transverse mode-locked (TML) laser beam were reconstructed from the measured spatial and spatio-temporal intensity distributions, respectively. The distribution of the reconstructed modal power coefficients revealed that the average mode order of the transverse mode-locking process could be increased by a factor of about 8 compared to previous works, corresponding to an increase in the normalized oscillation amplitude by a factor of about 3. Furthermore, we found that besides a non-Poissonian modal power distribution, strong aberrations of the modal phases occurred in the experiment, resulting in a deformation of the oscillating spot. Additionally, we demonstrated the generation of up to four spots oscillating simultaneously on parallel traces by operating the TML laser on a higher mode order in the orthogonal direction to the transverse mode-locking process. TML lasers are of interest, e.g., for beam scanning purposes, as they have the potential to enable spot resolving rates in the multi-GHz regime.

[en] In this paper, we report a method for rapid water quality evaluation based on laser-excited dissolved organic matter (DOM) fluorescence and water Raman peak. A formula, which results in the score from 0 to 100, was proposed to evaluate water quality. We first employed this method to evaluate the self-prepared water samples with humic acid or fulvic acid under different concentrations from 0.01 mg/L to 8 mg/L. In these experiments, the water samples were tested by our self-customed microlaser spectrometer. The good correlations between fluorescence intensity of DOM and concentrations of humic acid or fulvic acid were found. These results indicated that the method we proposed is reasonable on the water quality assessment. Furthermore, we evaluated water samples from five different sources and the results consisted well with the general knowledge of the water quality. These results demonstrated that this method offers a number of advantages for water quality evaluation including compact configuration, rapid test process, simple operation, and low cost.

[en] Compact nonlinear frequency conversion of a Y-branch distributed Bragg reflector (DBR) diode laser for alternating dual-wavelength laser emission at 532 nm is presented for the very first time. The developed light source, realized on a 5 × 25 mm² micro-optical bench, is based on single-pass second harmonic generation of a 1064 nm Y-branch DBR diode laser in a periodically poled lithium niobate waveguide crystal with superimposed poling periods. Phase-matching is obtained by intrinsic wavelength stabilization of the laser and wavelength tuning by implemented heater elements above the DBR gratings. Obtained optical output powers of 5.6 mW at 532.45 nm and 6.7 mW at 531.85 nm are limited by central lobe power contents of 52% available for waveguide coupling. With a spectral performance showing narrowband emission with spectral widths of 0.01 nm (0.4 cm⁻¹) limited by the spectral resolution of the spectrum analyzer and a spectral spacing of 0.6 nm (20 cm⁻¹), the developed light source is suitable for applications such as Raman spectroscopy and shifted excitation Raman difference spectroscopy (SERDS). Separate electrical contacts of the Y-branch diode laser enable alternating operation at both wavelengths.

[en] We report on the realization of a displacement sensor based on an optical nanofiber. A single gold nano-sphere is deposited on top of a nanofiber and the system is placed within a standing wave which serves as a position ruler. Scattered light collected within the guided mode of the fiber gives a direct measurement of the nanofiber displacement. We calibrated our device and found a sensitivity up to 1.2 nm/$\sqrt{\text{Hz}}$. As an example of application, a mechanical model based on the Mie scattering theory is then used to evaluate the optically induced force on the nanofiber by an external laser and its displacement. With our sensing system, we demonstrate that an external force of 1 pN applied at the nanofiber waist can be detected.

[en] In this work, the UV absorption cross sections of the fluorescence tracer 1-methylnaphthalene are determined in the range of 230–330 nm. The experiments are performed in a continuously scavenged gas flow cell, which allows for defined homogeneous conditions regarding temperature, pressure, and tracer/fuel composition. A LSDS (laser driven light source) is used for irradiation, which enables high spectral emission intensities in the UV range studied. For detection, a spectrograph in combination with an intensified camera is applied. Absorption cross sections at temperatures up to 850 K are determined and compared to sparsely available published data. Possible uncertainties caused by the optical setup and the flow cell, respectively, are considered.