Features of Brass Processing with Powerful Ultraviolet Lasers of Nanosecond Duration

We investigated the process of laser heat treatment of polished brass samples (36% zinc, containing a small amount of lead, which does not dissolve in the alloy and is in the form of inclusions, having micron and submicron size) by impacting to a series of 25 - 30 ultraviolet (UV) pulses of a Nd:YAG laser (third harmonic, wavelength λ = 355 nm, duration τ = 10 ns, pulse repetition rate f = 10 Hz, pulse energy density ~ 0.15 - 1.0 J/cm2) in the stationary spot mode. Copper and its alloys absorb up to 90% of the energy of this laser. It is found that the relaxation of the absorbed energy of laser radiation in the metal occurs nonuniformly. Defects in the metal structure such as grain boundaries and lead inclusions are visualized. Traces of crystallographic sliding appear inside some grains. With an increase in the number of impacting impulses, accumulation of damage is observed. A further increase in the radiation energy density leads to an aggravation of the observed phenomena.

Giant Third-Order Nonlinear Response of Mixed Perovskite Nanocrystals

Mixed (FAPbI3)0.92(MAPbBr3)0.08 perovskite thin films exhibit strong nonlinear optical responses, rendering them promising candidates for applications in photonics and optical communications. In this work, we present a systematic study on the ultrafast third-order nonlinear optical processes in mixed perovskite nanocrystals (NCs) by exploring the generation of third harmonic radiation and giant two-photon absorption-based photoluminescence (PL) when excited by femtosecond laser pulses of a 1030 nm central wavelength. A comparative analysis of the coherent third harmonic generation in the thin-film-containing perovskite nanocrystals has shown a 40× enhancement of the third harmonic signal compared to the signal generated in the pure quartz substrate. The cubic dependence of the third-nonlinear optical response of the (FAPbI3)0.92(MAPbBr3)0.08 perovskites on the intensity of the driving radiation was identified using broadband 38 femtosecond driving pulses. The positive nonlinear refractive index (γ = +1.4 × 10−12 cm2·W−1) is found to play an important role in improving the phase-matching conditions of the interacting pulses by generating a strong third order harmonic. The giant two-photon absorption (TPA)-assisted PL peak was monitored and a blue shift of the PL was obtained in the higher intensity range of the laser pulses, with the absorption coefficient β estimated to be~+7.0 cm·MW−1 at a 1030 nm laser wavelength.

Melanin diagnostics with nonlinear optics: a mini-review

Optical methods are widely used to perform fundamental studies of living systems and solve problems of biomedical diagnostics. Along with the classical spectroscopy, methods of nonlinear optics (e.g., multiphoton microscopy) are also applied in biophotonics. The potential of nonlinear optical methods for visualisation and analysis of the properties of endogenous chromophore molecules are considered in this minireview. Melanin - a pigment with specific spectral features of photophysical properties in the visible and near-IR ranges - is taken as an example. It is discussed what information about its localisation in tissues and structural organisation can be obtained by nonlinear optical methods: multiphoton fluorescence microscopy (including fluorescence lifetime imaging), third harmonic generation, pump - probe spectroscopy, and coherent anti- Stokes Raman spectroscopy.

Sensorless Control for Non-Sinusoidal Five-Phase Interior PMSM Based on Sliding Mode Observer

This paper proposes a sensorless control strategy based on Sliding Mode Observer (SMO) for a Five-phase Interior Permanent Magnet Synchronous Machine (FIPMSM), with a consideration of the third harmonic component. Compared to conventional three-phase machines, the third harmonic of back electromotive force (back-EMF) contains more information. Thus, in this paper, the first and third harmonic components of the five-phase machine are considered to estimate the rotor position which is necessary for the vector control. Simulation results are shown to verify the feasibility and the robustness of the proposed sensorless control strategy.

Estimation of soil temperature by Harmonic analysis

Soil temperatures recorded at 5.10 and 20 cm depth at Anand station of Gujarat state for the period of 1982-93 were analyzed by harmonic analysis and tested it for the year 1998. The amplitude of the soil temperature wave for the various depths decreases from a maximum of 5.76° C in the first harmonic to 0.96°C in the third harmonic. First, second and third harmonic explained 55 to 76 percent, 18 to 37 percent and 2 to 4 percent of the total variance, respectively. Total percentage of total variance covered by the three harmonics at different depths are in the range of 95 to 97 percentage for the period of 1982-93 normalized data series which shows the applicability of harmonic analysis in describing soil temperatures. The weekly observed and computed soil temperatures by harmonic analysis were in agreement and their differences were non significant by Chi-Square test.