Wavelength Of Laser Radiation Research Articles

Growth and characterization of α-nickel sulphate hexahydrate single crystal

Single crystal of α-nickel sulphate hexahydrate, α-NiSO4. 6H2O (α-NSH) is grown from aqueous solution by slow evaporation method. Solubility and metastable zone width of α-NSH are determined from the aqueous solution. The three dimensional structure is elucidated by single crystal X-ray diffraction studies. The α-NSH crystallizes in the non – centrosymmetric tetragonal space group P41212. The relative contributions of various intermolecular interactions involved in the crystal structure are quantified using Hirshfeld surface analysis and the decomposed two dimensional fingerprint plots. Fourier transform infrared spectral analysis and Vickers microhardness studies are carried out to characterize the grown crystal. Further the grown crystals are characterized using TGA, DSC, UV–Vis–NIR and dielectric analysis. The third order nonlinear optical properties are studied by Z–scan technique with HeNe laser radiation of wavelength 632.8 nm and the corresponding nonlinear refractive index, absorption coefficient and optical susceptibility are calculated. Crystalline perfection is assessed by etching studies and laser damage threshold is observed for the grown crystal.

Reversible phase–structure modification of photostructurable glass ceramic by CO2 laser irradiation

Structural changes and phase transformations of the photostructurable glass (PhG) surfaces under the impact of 10.6-μm wavelength laser radiation are examined. The regimes initiating the formation and development of crystalline phase and its reversible (secondary) amorphization are determined. In addition, the kinetic of crystalline phase formation and its melting on the surface of PhG are investigated. The characteristics of multiple reversible phase–structure transformations in the temperature range of 470–800 °C are investigated.

Autodyne interferometry for range-finding under laser radiation wavelength modulation

The results of solution of the inverse problem of determining the distance to the reflector in the case of current modulation of the laser radiation wavelength are presented. It is shown that current modulation of the autodyne signal amplitude can reduce the inverse problem of finding the distance to the reflector to a state of affairs characteristic only of phase modulation. The technique that we propose provides a higher range-finding accuracy than does direct analysis of the autodyne signal.

Generation of acoustic waves by cw laser radiation at the tip of an optical fiber in water

We investigate the specific features of acoustic signals generated in water under the action of cw laser radiation with a power of 3 W at wavelengths of 0.97, 1.56, and 1.9 μm, emerging from an optical fiber. It is established that when a fiber tip without an absorbing coating is used, quasi-periodic pulse signals are generated according to the thermocavitation mechanism due to the formation and collapse of vapor–gas bubbles of millimeter size. In this case, the maximum energy of a broadband (up to 10 MHz) acoustic signal generated only at wavelengths of 1.56 and 1.9 μm is concentrated in the range of 4–20 kHz. It is shown that when there is no absorbing coating, an increase in the laser-radiation absorption coefficient in water leads to an increase in the frequency of generated acoustic pulses, while the maximum pressure amplitudes in them remain virtually constant. If there is an absorbing coating on the laser-fiber tip, a large number of small vapor–gas bubbles are generated at all laser-radiation wavelengths used. This leads to the appearance of a continuous amplitude-modulated acoustic signal, whose main energy is concentrated in the range of 8–15 kHz. It is shown that in this case, increasing the absorption coefficient of laser radiation in water leads to an increase in the power of an acoustic emission signal. The results can be used to explain the high therapeutic efficiency of moderate-power laser-fiber apparatus.

Laser sintering of a TiO2 nanoporous film on a flexible substrate for application in solar cells

The selective laser sintering of TiO2-film nanoparticles on a plastic conductive substrate is considered for application in flexible dye-sensitized solar cells. It is shown that the absorbed energy of the laser radiation during laser sintering promotes electrical-contact formation between TiO2 nanoparticles without damaging the plastic conductive substrate. The choice of a near-infrared laser radiation (wavelength of 1064 nm) provides an efficient laser-sintering process. The laser-sintering method promotes a decrease in recombination losses in the TiO2 film and an improvement in the charge-collection efficiency, which can result in an increase in the efficiency of such solar cells. Furthermore, the efficient-laser sintering method has a great potential for application in the roll-to-roll technology of the fabrication of high-efficiency flexible solar cells.

Spectroscopic and laser properties of bulk iron doped zinc magnesium selenide Fe:ZnMgSe generating at 4.5 - 5.1 µm.

The Fe:Zn(1-x)Mg(x)Se (x = 0.19, 0.27, and 0.38) solid solutions spectroscopic properties were investigated and laser oscillations were achieved for the first time. The increase of the magnesium concentration in the Fe:ZnMgSe crystal was shown to result in an almost similar long wavelength shift of both absorption and fluorescence spectra of about 60 nm per each 10% of magnesium. With the Fe:ZnMgSe crystal temperature decrease, the fluorescence spectrum maximum shifts towards shorter wavelength resulting mainly from strong narrowing of the longest wavelength fluorescence line. Laser radiation wavelength dependence on the magnesium concentration as well as on temperature was observed. The Fe:ZnMgSe x = 0.38 laser oscillation wavelength increased from 4780 nm at 80 K to 4920 nm at 240 K using the optical resonator without any intracavity spectrally-selective element. In comparison with the Fe:ZnSe laser operating in similar conditions, these wavelengths at both temperatures were shifted by about 500 nm towards mid-IR region.

Color digital lensless holographic microscopy: laser versus LED illumination.

A comparison of the performance of color digital lensless holographic microscopy (CDLHM) as utilized for illumination of RGB lasers or a super-bright white-light LED with a set of spectral filters is presented. As the use of lasers in CDLHM conceals the possibility of having a compact, lightweight, portable, and low cost microscope, and additionally the limited available laser radiation wavelengths limit a real multispectral imaging microscope, here we present the use of super-bright white-light LED and spectral filters for illuminating the sample. The performance of RGB laser-CDLHM and LED-CDLHM is evaluated on imaging a section of the head of a Drosophila melanogaster fly. This comparison shows that there is trade-off between the spatial resolution of the microscope and the light sources utilized, which can be understood with regard to the coherence properties of the illuminating light. Despite the smaller spatial coherence features of LED-CDLHM in comparison with laser-CDLHM, the former shows promise as a portable RGB digital lensless holographic microscope that could be extended to other wavelengths by the use of different spectral filters.

Effects of laser irradiation on a bloom forming cyanobacterium Microcystis aeruginosa.

Effects of laser irradiation on photosystem II (PS II) photochemical efficiencies, growth, and other physiological responses of Microcystis aeruginosa were investigated in this study. Results indicate that laser irradiation (wavelengths 405, 450, 532, and 650nm) could effectively inhibit maximal PS II quantum yield (Fv/Fm) and maximal electron transport rates (ETRmax) of M. aeruginosa, while saturating light levels (Ek) of M. aeruginosa did not change significantly. Among the four tested wavelengths, 650nm laser (red light) showed the highest inhibitory efficiency. Following 650nm laser irradiation, the growth of M. aeruginosa was significantly suppressed, and contents of cellular photosynthetic pigments (chlorophyll a, carotenoid, phycocyanin, and allophycocyanin) decreased as irradiation dose increased. Meanwhile, laser irradiation enhanced the enzyme activities of superoxide dismutase (SOD) and peroxidase (POD) in M. aeruginosa cells. Lower irradiation doses did not change the intracellular microcystin contents, but higher dose irradiation (>1284Jcm-2) caused the release of microcystin into the culture medium. Transmission electron microscope examination showed that the ultrastructure of M. aeruginosa cells was destructed progressively following laser irradiation. Effects of laser irradiation on M. aeruginosa may be a combination of photochemical, electromagnetic, and thermal effects.

The Effects of Laser Wavelength and Particle Size on Heating and Melting of Gold Nanoparticles Dispersed in Liquid

In this research the heating process and melting of water surrounded homogenous gold nanospheres irradiated by nanosecond laser pulses at the wavelengths of 355, 532, 633, and 900 nm are studied. The estimation of absorbed energy by gold nanoparticles with radius range 1-40 nm and their maximum temperature is calculated using the absorption efficiency of the nanoparticles at corresponding laser wavelength. The dependency of the melting temperature of nanoparticles upon their size is also considered. It is seen that the progress in the melting process strongly depend on the laser wavelength and particle size. The laser wavelength of 532 nm has been found appropriate for effective photothermal heating of a large gold nanoparticle. Controlling the laser irradiation wavelength is crucial to achieve the best conditions for the desired applications such as localized heating and nanowelding.

Pulsed Laser Porosification of Silicon Thin Films.

We present a new and simple laser-based process to porosify thin film silicon using a pulsed laser. During deposition, we incorporate gas atoms or molecules into the Si thin film. Pulsed laser radiation of wavelength heats up thin film Si beyond its melting point. Upon heating, gas atoms or molecules form nm-sized thermally expanding gas bubbles in the silicon melt, until they explosively exit the film, leaving pores behind. Rapid heating and fast cooling during pulsed laser processing enable re-solidification of the liquid Si before the created pores contract and pore closure occurs within the liquid phase. Optimized plasma-enhanced chemical vapor deposition or sputtering of amorphous Si thin films on stainless steel substrate incorporates the necessary concentration of gas atoms or molecules. We are able to tailor the pore size between 50 and 550 nm by changing laser pulse energy density and film deposition parameters. Evaporated silicon containing no gas atoms forms only a few very large m-sized gas bubbles due to laser-induced vapor formation of evaporated solid material at the substrate–silicon interface.

Noncritically phase-matched fourth-harmonic generation of Nd:glass lasers and design of final optics assembly

The noncritically phase-matched (NCPM) fourth-harmonic generation (FHG) with partially deuterated dihydrogen phosphate (KD*P) crystal at an Nd:glass laser radiation wavelength of 1053.1nm has been confirmed. NCPM FHG has been achieved in 70% and 65% deuterated KD*P crystal at the temperature of 17.7°C and 29.3°C, respectively. The angular acceptance of 70% and 65% deuterated KD*P crystals fixed at their NCPM temperature were measured, which were 53 and 55mrad, respectively. The application of the NCPM FHG in a high-power laser facility for inertial confinement fusion is also discussed. Based on the theoretical analysis, the NCPM KD*P can be placed after the focus lens; thus, the laser-induced damage of a fused-silica lens at ultraviolet can be avoided.

Reconstructing the distribution function of particles over sizes based on the data of multiwave laser probing

This paper presents a new semi-empirical method of solving the inverse laser-probing problem for the particles of a polydisperse aerosol. Measuring the optical density of an air flow of aerosol particles at three wavelengths of the probe laser radiation made it possible to obtain the mean volume-surface size of the particles, which is associated by correlation dependences with the parameters of the scattering function of the particles over sizes. Good agreement is obtained with the data of direct measurements for the particles of a cement aerosol.

Periodic colour-centre structure formed under filamentation of mid-IR femtosecond laser radiation in a LiF crystal

A colour-centre structure formed in a LiF crystal under filamentation of a femtosecond mid-IR laser pulse with a power slightly exceeding the critical power for self-focusing has been experimentally and theoretically investigated. Strictly periodic oscillations have been detected for the first time for the density of the colour centres induced in an isotropic LiF crystal under filamentation of a laser beam with a wavelength tuned in the range from 2600 to . The structure period is found to be about . With an increase in the laser radiation wavelength, the period of the oscillations decreases and their amplitude increases. The maximum colour centre density, observed under filamentation of a beam, is related to the increased contribution of the direct generation of colour centres as a result of the absorption of an integer number of photons by the exciton band. It is numerically shown that the formation of a periodic colour-centre structure in LiF is due to the periodic change in the light field amplitude in the light bullet (1.5 optical periods long) formed under filamentation.

Localized surface plasmon polaritons and nonlinear overcoming of the diffraction optical limit

Experimental results on the formation of ordered structures on the surface and in the near-surface layer of condensed media under the action of linearly polarized laser radiation pulses are analyzed. The formation of subdiffraction nanostructure gratings with anomalous orientation is discussed in the context of the universal polariton model. A physical model of the formation of anomalous structure gratings with periods much less than the laser radiation wavelength is proposed and experimentally verified. The model is based on excitation and mutual interference of channel (wedge) surface plasmon polaritons.

Analysis of measurement errors for Thomson diagnostics of non-Maxwellian plasmas in tokamak reactors

The study is stimulated by the expected noticeable deviation of the electron velocity distribution function (eVDF) from a Maxwellian under condition of a strong auxiliary heating of electron plasmas in tokamak-reactors. The key principles of accuracy estimation of the Thomson scattering diagnostic of non-Maxwellian plasmas in tokamak-reactors are presented. The algorithm extends the conventional approach to the assessment of non-Maxwellian plasmas measurements errors for a broad class of deviations of the eVDF from a Maxwellian. The algorithm is based on solving the inverse problem many times to determine main parameters of the eVDF with allowance for all possible sources of error and statistical variation of the input parameters of the problem. The method is applied to a preliminary analysis of the advantages of the formerly suggested use of various wavelengths of probing laser radiation in the Thomson diagnostics of non-Maxwellian plasma on the example of the core plasma Thomson scattering diagnostic system which is under design for ITER tokamak. The results obtained confirm the relevance of the diversification of the probing laser radiation wavelength.

Time of flight for photon in human skin

The time of flight for photons in human skin was measured using picosecond diode laser. Two different wavelength lasers were used - 405 nm and 510 nm. A difference for time of flight in normal skin and in nevus was observed as well as a difference for different wavelength laser irradiation was observed. For 405 nm laser irradiation the difference was 41 ps while comparison of time of flights skin and nevi using 510 nm irradiation showed a result of 32 ps. Results allow to conclude that the time photon travels in skin might depend on the characteristics of the medium and wavelength of the irradiation. This can be related to known data for light penetration depth in human skin for different wavelengths.

Стабилизация длины волны излучения диодных лазеров. Динамические характеристики элементов Пельтье

Стабилизация длины волны излучения диодных лазеров. Динамические характеристики элементов Пельтье

Growth and characterization of semiorganic single crystal of bis-glycine manganese chloride

Semiorganic single crystals of bis-glycine manganese chloride (BGMC) of dimension 5×3×3mm3 were grown from aqueous solution by slow evaporation method at room temperature. The crystal structure and lattice parameters were determined for the grown crystal by the single crystal X-ray diffraction studies. BGMC was subjected to FT-IR and FT-Raman spectral analyses. The lower cutoff wavelength observed from UV–vis–NIR transmittance spectrum is 271nm. The mechanical strength of the grown crystal was estimated using Vickers microhardness tester. The dielectric response of the grown crystal was analyzed at different temperatures in the frequency range from 50Hz to 2MHz. Thermal properties were investigated by thermogravimetric, differential thermal and differential scanning calorimetric analyses. Chemical etching study shows the distribution of etch figures of various shapes in the grown single crystal. The third order nonlinear optical properties of BGMC were investigated by Z-scan technique employing He–Ne laser radiation of wavelength at 632.8nm.

A digital system of fluorescence visualization for antibacterial photodynamic therapy in dentistry

In the present work, a novel compact system for visualizing the spatial intensity distribution of the photosensitizer fluorescence for antibacterial photodynamic therapy in dentistry is suggested. The compact intraoral system includes a visible imaging camera and a violet laser diode. The wavelength of laser radiation is matched to the short-wavelength absorption peak of Photoditazin, so the effective excitation of its fluorescence is ensured. The built-in spectral-selective optical filter allows the camera to detect only the spatial distribution of the fluorescence intensity while the excitation radiation is blocked. Intraoral fluorescent images obtained with the suggested system can be used for diagnosis of residual amount of pathogens.

Study for Improving Laser Beam Welding Efficiency

The aim of this paper is to highlight a method for improving laser beam efficiency. The laser weld bead profile depends on various parameters such as beam power, welding speed, wavelength of the laser radiation or the initial temperature of the material. Taking into account that laser beam welding efficiency is usually limited by synchronization of the laser source parameters, new methods were developed. In this paper is analyzed the influence of preheating the material and of the wavelength of laser radiation on the laser weld bead profile. Improvement in penetration depth was noted for preheating the material to around 140°C.