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Colour Sensor White Balance Influence on White-Light Interferometer Resolution
Full text linkImpact of a sensor color balance on white-light fullfieldoptical coherence tomography (FF-OCT)resolution is investigated in the paper. Full width athalf magnitude (FWHM) of a coherence pulse wascalculated for various white balance (WB) settings.Simulated dependence of FWHM on WB of asensor and experimental data are shown in thepaper. The minimum interference pulse width canbe achieved by the proper color balance coefficientschoice. And in this case the pulse is narrower thaneither one registered by colour image sensor withWB based on light source emission spectrum or bymonochrome image sensor
Kerr-lens mode locking in a ring bidirectional YAG:Cr4+ laser
Full text linkThis paper concerns a bidirectional ring YAG:Cr4+lаser. We investigated the features of bidirectional generation and explored the possibility of gyroscopic effect in the laser. We developed the model of bidirectional generation of such a laser taking into account spectral properties of the active medium.Experiments in our setup revealed that generation of the laser had a cluster character. Luminescence spectrum of the YAG:Cr4+ crystal and generation spectra of the laser showed that this medium has both homogeneous and inhomogeneous broadenings. Stable bidirectional generation is a result of the fact that competition between counterpropagating waves is less than in the case of homogeneously broadened medium
Raman structural study of random olefin copolymers
Full text linkIn this work we present Raman study of random copolymers of ethylene and propylene with a number of α-olefins, and investigation of the relationships between the spectral characteristics of the Raman lines and the copolymer structural properties. For both the copolymers we observed rapid decrease in the crystallinity and conformational order as the content of the incorporated monomer increases
All-Fiber Thulium-Doped Mode-Locked Lasers Based on the Nonlinear Amplifying Loop Mirror
Full text linkWe report on thulium-doped all-fiber lasers based on the nonlinear amplifying loop mirror and mode-locked by both a semiconductor saturable absorber (SESAM) and single-walled carbon nanotubes (SWCNT). An intracavity and external dispersion management was realized with the aid of a passive germanium-silicate fiber. SESAM mode-locked laser generates as short as 230-fs pulses with maximum average output power of 106 mW, corresponding to a 3.7 kW peak power and almost 2 nJ pulse energy. In contrast to SESAM-based laser, the SWCNT mode-locked laser generates 450-fs pulses of mW-level average output power respectively
Boundary Condition Effect On Photoacoustic Response Of Absorbing Liquid To Modulation Of Laser Intensity
Full text linkThe photoacoustic (PA) pressure response of the absorbing liquid (water, ethanol) with free and confined surface to laser pulse with modulated intensity is studied. Modulation amplitude of the PA signal demonstrates non-monotonous behavior during laser pulse action which can be explained as interference between thermo-acoustic and vaporization mechanisms of pressure generation. The phase behavior of modulated part of PA signal also gives important information on processes in the irradiated matter. Doppler photoacoustic monitoring (DPM) is used to determine surface movement during laser irradiation (wavelength – 2.94 um, pulse duration ~ 200-300 ns, fluence ~ 0.3-1.6 J/cm2). In the case of free surface this movement is possible into the upward and downward directions while for the constrained irradiated surface only one movement is supposed. This supposition is in agreement with the experiment. However the total behavior of PA response is more complicated due to probably vapor cavity formation between liquid and solid surfaces. In particular, despite the imposed constraint PA response behavior resembles the free surface case
Mechanism of femtosecond laser nano-ablation for metals
Full text linkMetals have three ablation threshold fluences (high,middle and low-threshold fluence, here called) forfemtosecond laser pulses. In order to investigatethe physics of metal ablation under an intenseoptical field, the ions emitted from a laserirradiatedcopper surface were studied by time-offlightenergy spectroscopy. The low laser fluenceat which ions are emitted, Fth,L is 0.028 J/cm2, andtwo higher emission thresholds were identified atfluences of Fth,M =0.195 J/cm2 and Fth,H =0.470J/cm2. The relation between the number of emittedions per pulse Ni and laser fluence F was in goodagreement with Ni ∝F4 for Fth,L - Fth,M, Ni ∝F3 forFth,M - Fth,H, and Ni ∝F2 for ≥ Fth,H. Thedependence of ion production on laser energyfluence is explained well by multiphotonabsorption and optical field ionization.For fluence levels near the middle to high ablationthreshold, the formation of grating structures onmetal surfaces has been observed. The interspacesof grating structures were shorter than the laserwavelength, and the interspaces depend on fluencefor Mo and W with a 160 fs laser pulse. Thisphenomenon is well explained by the parametricdecay model proposed by Sakabe et al
Observation of Thermocapillary Effect in Gas -Assisted CO2 Laser Cutting of Steel
Full text linkInvestigations of melt’s dynamics have been performed with pyrometer in the gasjet-assisted CO2 laser cutting. Pyrometer consists of 4 sensors and local luminosity of metal melt has been measured precisely on different depth along front of cutting with long dimension resolution about 0.1 mm and with time resolution as short as 0.06 ms. The results of data processing of brightness temperature are reported for laser cutting of mild-steel plate 3 mm, 6 mm and 10 mm thick, that allows obtaining spectra of melt’s surface deformation for different values of cutting velocity and assisted gas pressure. The generation of capillary-wave turbulence following thermo-capillary effect can be observed in the locations, where intensity of radiation of CO2 laser on melt’s surface exceeds 1 MW/cm2. The R-M-S of temperature fluctuations is greater than 10 K in the range of sub-millimeter capillary waves. Thus, an additional mechanism of the anomalous absorption on the front of cutting can compensate the low absorption of the metal in case of 10.6 μm laser in comparison with the absorption of the metal in the near infrared range
Light Scattering Microscopy for Tumor Cell Recognition
Full text linkLight scattering microscopy is suggested to providesome insight into cell architecture and to giveinformation on cell malignancy or morphologicalchanges upon necrosis or apoptosis. In the presentpaper a microscope setup for scattering experimentswith high angular resolution is reported, and firstdata obtained from test models (polystyrene beads),cell monolayers and 3-dimensional cell spheroidsare reported. Data are compared with simulationsbased on Mie scattering and discussed in view oftheir possible use for tumor cell recognition withintissue samples. The discussion includes presentlimitations due to spatial resolution or inhomogeneous illumination and suggests possibilities ofimprovement
Growth peculiarities and non-linear properties of profiled doped strontium-barium niobate crystals
Full text linkThe nominally pure and doped with Ce, Cr, Co strontium-barium niobate crystals of SBN:61 were grown by modified Stepanov technique. The specific features of the technique were studied and growth conditions for obtaining the high homogeneous SBN crystals in bulk-profiled configuration were optimized. The photorefractive and non-linear properties of SBN pure and doped with Ce, Cr and Co were investigated. It was shown that SBN:Ce crystal is an excellent medium for high efficiency holographic information recording. SBN:Cr and SBN:Co crystals are promising photorefractive materials with short response time. The as-grown SBN crystals were also used to demonstrate the diffuse noncollinear second harmonic generation emitted by a random domain SBN structure and Stimulated Raman Scattering and two-photon absorption associated with cubic nonlinear susceptibility of the materials
Development of the Methods of Control of Radiation Structure of
Full text linkSpecific features of radiation structure of terahertz quantum cascade lasers are determined by wire geometry of their waveguides with small and sub-wavelength transverse dimensions and the length much larger than the wavelength. Here we present an overview of the results of beam profile investigations and of the methods proposed for the control of radiation structure of such lasers
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