Analysis of all-optical light modulation in proteorhodopsin protein molecules

All-optical switching has been theoretically analyzed in LOV2 phototropin, the blue light plant photoreceptor based on nonlinear intensity-induced excited-state absorption. The transmission of a cw probe laser beam at 660 nm through LOV2 protein can be controlled by a cw or pulsed pump laser beam at 442 nm, respectively. This modulation is sensitive to the small-signal absorption coefficient, absorption cross-section of the excited L-state at pump beam wavelength and sample thickness. It is shown that the unique spectral and kinetic properties of wild-type LOV2 and LOV2-C39A mutant, result in the probe beam getting completely switched off (100% modulation), by the pump laser beam of intensity 50 kW/cm² and 1 kW/cm², respectively. The switching response in LOV2-WT is faster (~μs) than in LOV2-C39A mutant (~ms). The results have been used to design an optically-addressed spatial light modulator and all-optical NOT, and the universal NAND and NOR logic gates. The results show the applicability of this novel plant photoreceptor protein for photonic applications.

Upconversion luminescence and hypersensitive transitions of [formula omitted]–doped calcium aluminosilicate glasses

Two multi-kilowatts Nd: YAG laser beams are condensed separately and combined at surface of workpiece in order to increase penetration depth. In this system, one or two laser beams are inevitably inclined depending on size of condensing optics, thus, welding characteristics might be fairly complicated than that of a single laser beam welding. Welding characteristics are evaluated by penetration depth and penetration shape in bead-on-plate tests of stainless steel (304). This paper is intended as an investigation on the welding condition of the deepest weld penetration, especially on arrangement of condensing optics. The deepest weld penetration of 6.3 and 7.7 mm are obtained by two CW laser beams and two rectangularly modulated CW laser beams with total average power of four kilowatts at a welding speed of 5 mm/s, respectively. Deepened penetration depths of weld beads by laser beams in combination due to the increase in total laser power are obtained in comparison to penetration depths of 2.8 and 4.3 mm by a single CW laser beam and a single rectangular modulated CW laser beam with average powers of two kilowatts, respectively. Penetration depths of weld beads obtained with symmetric irradiation exceed those with asymmetric irradiation. The angle between two laser beams for the deepest penetration is 60 degrees for CW laser beams, while the angle is 30 degrees for modulated CW laser beams. The difference in the appropriate angles for the deepest penetration might be explained by different effect of keyhole bottom separation on penetration depths depending on waveform of laser beams. With asymmetric beam arrangement, a deeper penetration is obtained in backhand welding direction for the inclined laser beam than that in forehand direction both in welding using two CW laser beams in combination and two modulated CW beams in combination.

Optimization of radial smoothing scheme for improving illumination uniformity of laser quad

Metabotropic glutamate receptor modulation of synaptic transmission in corticostriatal co-cultures: Role of calcium influx

We already discussed the bistable behavior of a Fabry Perot resonator filled with molecular media as well as the characteristics of a spatial light modulator (SLM) based on the nonlinearity induced by excited state absorption. In the present paper we present two practical configurations. First we analyze a cavity-less bistable element which removes some of the realization problems related to high finess cavity. In this configuration the nonlinear medium is located in one arm of an optical interferometer. The scheme provides the required amount of positive feedback by the bistable mechanism -- but without a cavity. We applied the nonlinear eikonal approximation, a method which takes care of the detailed propagation effects, and obtained conditions for bistability, as well as optimizing the design parameters such as the output mirror reflectivity, etc.

The widely established techniques for the generation of ultrashort optical pulses rely on passive mode locking of lasers, with the output pulse duration and emission spectrum determined by the intrinsic lifetime of laser transition in the gain medium. Due to the instantaneous nature of nonlinear gain, optical parametric oscillators (OPOs) are capable of generating optical radiation in all timescales from continuous-wave (cw) to ultrashort femtosecond regime, if driven by laser pump sources in the corresponding time domain. In the ultrashort timescale, operation of OPOs conventionally relies on mode-locked pump lasers, with the concomitant disadvantages of large footprint and high cost. At the same time, the lack of gain storage mandates the use of synchronous pumping, resulting in increased complexity. In this paper, we present the concept of phase-modulated OPO driven by cw pump laser. The approach overcomes the traditional drawbacks of ultrafast OPOs, enabling femtosecond pulse generation without the need for synchronous pumping, resulting in a simplified, compact, and cost-effective architecture using cw input pump lasers. We derive a mean-field equation for a degenerate χ(2) OPO driven by a cw laser with intracavity electro-optic modulator (EOM), and also including dispersion compensation. The equation predicts the formation of stable femtosecond pulses (<200fs), in both normal and anomalous dispersion regimes, with a controllable repetition rate determined by the frequency of the EOM. The remarkable functionality of the proposed scheme paves the way for the development of an alternative class of widely tunable coherent femtosecond light sources in both bulk and integrated format based on χ(2) OPOs using cw pump lasers. Published by the American Physical Society 2024

The trapping process of the biological micro-particle in the tweezers using CW laser beam has been investigated in series of our works. In the CW regime, the dynamics of polystyrene microsphere linking to λ-phage DNA molecule depending on the optical force, Brown force and its elastic force are simulated and discussed. In this paper we present the finite difference Langevin equation (FDLE) describing the dynamics of trapped bead linking to DNA molecules in an optical tweezers. Using FDLE the dynamics, i.e., the position-time characteristics of polystyrene microsphere linking to λ-phage DNA molecule are simulated in the pulse regime. The obtained results show that all principle parameters as the peak intensity, beam waist radius, and duration of pulsed Gaussian laser beam, well as the setting-up position of DNA molecule influence on the dynamics, especially on the “pulling” and “stability” times of trapped bead. The conditions for λ-phage DNA molecule in stretching state are discussed for experimence.

A new class of position-sensitive detectors has been developed at Los Alamos Scientific Laboratory (LASL). These detectors utilize Seebeck effect and thermal diffusion in the detector material (Si). Large area (up to 125 cm2) detectors with only four electrodes yield accurate x-y position sensing for cw and pulsed laser beams. The detectors are sensitive to any laser wavelength and feature high optical damage thresholds (>109 W/cm2 at 10 μm). The detector responses are found to agree accurately with a thermal diffusion model that has no adjustable parameters. These detectors are currently in use on Helios and are planned for use on Antares, the LASL laser fusion systems.© (1980) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

In this paper we report the experimental results obtained when an He-Ne laser beam crosses an MBBA homeotropic sandwich structure and is modulated by the influence of another laser beam, in our case an Ar+ laser, crossing through the same region. We extend some results previously reported by us12 concerning the influence of the ratio of the diameters of the laser beams on the modulation characteristics. A theoretical model, based on the one reported in Ref6, shows good agreement with the experimental results. If the Ar+ laser is intensity chopped, the resulting He-Ne diffracted image is also intensity modulated. The highest frequency observed has been 500 p. p. s.

We demonstrate continuous scanning of a dissipative Kerr micro-resonator soliton comb (hereafter called soliton comb). Detuning between a cw pump laser and a resonance of a microresonator is fixed via Pound-Drever-Hall (PDH) locking during scanning so as to maintain soliton operation. We show continuous comb mode scanning of as large as 190 GHz by heating the microresonator. In addition, with the frequency-scanned soliton comb, we demonstrate broadband, high resolution spectroscopy, showing spectral features with a bandwidth of as small as 5 MHz, while covering more than 2 THz spectrum.

“Rabilé” is a popular traditional ferment in Burkina Faso, consisting mainly of yeasts. It is used as a food supplement or additive like Single Cell Protein (SCP). The present work focused on identifying yeast microbiota in local food, and studying their growth kinetic parameters. “Rabilé” sampling from the 13 regions of Burkina Faso was used to isolate yeast strains. Molecular methods, including PCR-RFLP, Sanger Sequencing, and Single Locus Analysis, were applied for strain identification. The kinetic parameters were determined in batch culture. The results show 390 isolates belonging to 12 species with a predominance of Saccharomyces cerevisiae, followed by Cutaneotrichosporon curvatus. Among the selected strains, S. cerevisiae OG22 and Kluyveromyces marxianus KY01 showed the highest maximum growth rate (0.566 and 0.568 h-1) concerning kinetic parameters. These results demonstrate that “Rabilé” is an important biotope of yeast strains, and could be a potential food supplement.   Key words: Yeast, Rabilé, traditional ferment, molecular identification, kinetic parameters.

: Ions exhibiting broad fluorescence bands in the 5000A to 10,000A region have been studied as potential lasing ions in various glass hosts. Included in the study were Eu(2+), Cu(+), Sn(2+), Sb(2+), Yb(2+), Ge(2+), and CdS. Glass hosts included silicates, borates, and phosphates. Spectral data were used to calculate peak emission cross sections and flashlamp pumping thresholds for various ion-host combinations. These data indicated that Eu(2+) should lase easily. Cu(+), Sn(2+), and Sb(2+) should also lase but would require significantly greater pumping energies. Gain (loss) measurements were made on selected glass rods by passing a CW laser beam through the rods during flashlamp pumping. No gain was measured. Instead, most rods showed a pumped absorption. This absorption was probably due to transient color center formation in the glass hosts themselves, rather than excited state absorption by the dopant ions. Flashlamp pumping studies of several of the ions in various hosts selected for low pumped absorption is recommended as further work. Also recommended is laser pumping, which would eliminate the shorter wavelength ultraviolet primarily responsible for color center formation. (Author)

Energy distribution, intensity modulation and emittance of the beam extracted from a duopigatron source

Metallo-beta-lactamases (MbetaLs) are zinc-dependent enzymes able to hydrolyze and inactivate most beta-lactam antibiotics. The large diversity of active site structures and metal content among MbetaLs from different sources has limited the design of a pan-MbetaL inhibitor. Here we report the biochemical and biophysical characterization of a novel MbetaL, GOB-18, from a clinical isolate of a Gram-negative opportunistic pathogen, Elizabethkingia meningoseptica. Different spectroscopic techniques, three-dimensional modeling, and mutagenesis experiments, reveal that the Zn(II) ion is bound to Asp120, His121, His263, and a solvent molecule, i.e. in the canonical Zn2 site of dinuclear MbetaLs. Contrasting all other related MbetaLs, GOB-18 is fully active against a broad range of beta-lactam substrates using a single Zn(II) ion in this site. These data further enlarge the structural diversity of MbetaLs.