Laser Beams Of Different Wavelengths Research Articles

Light sheet fluorescence microscopy with active optical manipulation.

We present a light sheet fluorescence microscopy (LSFM) with active optical manipulation by using linear optical tweezers (LOTs). In this method, two coaxially transmitting laser beams of different wavelengths are shaped using cylindrical lenses to form a linear optical trapping perpendicular to the optical axis and an excitation light sheet (LS) parallel to the optical axis, respectively. Multiple large-sized polystyrene fluorescent microspheres are stably captured by LOTs, and their rotation angles around specific rotation axes are precisely controlled. During a sample rotation, the stationary excitation LS scans the sample to obtain fluorescence sectioning images of the sample at different angles.

Photoacoustic detection of transient phase transformation of nanoparticles.

The controllable preparation of spherical micro/nano particles of various materials has been achieved via the technology of the laser synthesis and processing of colloids (LSPC) recently. However, there is limited in situ research on the evolution processes of nanoparticles in photothermal transient environments, such as solid-state crystal transformations and changes of state, which limits the understanding and application of LSPC. Photoacoustic (PA) signals are sensitive to the optical, thermal and elastic properties of the medium, and can be used to measure the thermal and spectroscopic properties of matter. In this paper, the PA signals generated by the interaction of the laser with the surrounding liquid medium (ethanol, water, glycerin, etc.) and nanoparticles (Ag, TiO2, CeO2, ZrO2, etc.) are studied when the tunable LSPC technique provides different photothermal conditions (such as thermal expansion, solid crystal transformation and evaporation). It is found that semiconductors with different bandgaps, as light absorbers, have the ability to selectively absorb laser beams of different wavelengths. By changing the wavelength, the PA intensity can be adjusted accordingly. In addition, based on the fast laser heating and tunable fluence characteristics of non-focused laser beams in LSPC technology, transient processes such as material phase transitions and changes of state can be excited separately by adjusting the laser fluence. Taking titanium dioxide as an example, the PA signals generated by laser selective excitation of A-R (anatase into rutile) phase transitions and rutile vaporization can be detected.

Design of compact high resolution imaging system for cold atom experiments

In cold atom experiments, high resolution imaging systems have been used to extract <i>in-situ</i> density information when studying quantum gases, which is one of the hot topics in this field. Such a system is usually called “quantum-gas microscope”. In order to achieve a long working distance and large magnification, high resolution imaging of cold atoms through a vacuum window usually requires a long distance between the atoms and the camera. However, due to space limitation caused by a large number of nearby optical elements, it may be difficult to realize a long imaging system, which is a common case in cold atom experiments. Herein we present an imaging system that can achieve a short distance between the atoms and the image plane with diffraction-limited 1 μm resolution and 50 magnification. The telephoto lens design is adopted to reduce the back focal length and enhance the pointing stability of the imaging lens. The system is optimized at an operating wavelength of 767 nm and corrects aberrations induced by a 5-mm-thick silica vacuum window. At a working distance of 32 mm, a diffraction-limited field of view of 408 μm is obtained. The simulation result shows that by changing the air space between lenses, our design operates across a wide range of window thicknesses (0–15 mm), which makes it robust enough to be used in typical laboratories. This compact imaging system is made from commercial on-shelf <i>Φ</i>2 in (1 in = 2.54 cm) singlets and consists of two components: a microscope objective with a numerical aperture of 0.47 and a telephoto objective with a long effective focal length of 1826 mm. Both are infinitely corrected, allowing the distance between them to be adjusted to insert optical elements for irradiating atoms with laser beams of different wavelengths without affecting the imaging resolution. Taking the manufacturing and assembling tolerances into consideration, the Monte Carlo analyses show that more than 95% of the random samples are diffraction-limited within the field of view. This high success rate ensures that these two objectives can be achieved easily in the experiment. Combined with its performance with other wavelengths (470–1064 nm), this imaging system can be used for imaging different atom species, such as sodium, lithium, and cesium.

Design and Research of a Color Discrimination Method for Polycrystalline Silicon Cells Based on Laser Detection System

In this paper, a method of color discrimination based on sample sensitivity to light wavelength is proposed based on the reflection spectra of a large number of samples and the statistical calculation of the measurement data. A laser detection system is designed to realize the color discrimination. For the color discrimination of polycrystalline silicon cells, the most sensitive wavelength, 434 nm, and the least sensitive wavelength, 645 nm, of polycrystalline silicon cells is obtained according to this method. A laser detection system was built to measure the polycrystalline silicon cells. This system consists of two lasers, optical shutters, collimating beam expanding systems, an optical coaxial system, sample platform, collecting lens, and optical power meter or optical sensor. Two laser beams of different wavelengths are beamed coaxially through the optical coaxial system onto a polycrystalline silicon cell and are reflected or scattered. The reflected or scattered lights are collected through a lens with a high number aperture and received separately by the optical power meter. Then the color value of the polycrystalline silicon cell in this system is characterized by the ratio of light intensity data received. The system measured a large number of previous polycrystalline silicon cells to form the different color categories of polycrystalline silicon cells of this system in the computer database. When a new polycrystalline silicon cell is measured, the color discrimination system can automatically classify the new polycrystalline silicon cell to a certain color category in order to achieve color discrimination.

Synthesis and Characterization of Zinc Oxide Nanoparticles for Application in the Detection of Fingerprints

Stable zinc oxide nanoparticles were prepared by chemical process. Zinc oxide nanoparticles were synthesized using a modified method with zinc nitrate and sodium hydroxide at 60° C. The synthesized nanopowders were characterized in terms of chemical composition (EDS), structure FTIR and XRD, particle size and morphology by TEM. The XRD results confirm that ZnO nanoparticles were obtained with hexagonal arrangement (Wurtzite). The nanoparticles showed sizes between 10 to 30 nm and semispherical forms. The luminescent properties of the synthesized nanoparticles were measured in a photoluminescence assay on a Raman instrument. The samples were irradiated with two laser beams of different wavelengths. The application of the fingerprints on different surfaces was done using deferments surfaces.

Jet delivery system for Raman scattering on bio-inorganic compounds

We present a micro-jet sample delivery system for Raman measurements. Compared to cuvette measurements, the observed Raman signal is enhanced by more than one order of magnitude and does not contain signal distortions from the liquid-glass interface. Furthermore, the signal stability of repeated measurements is enhanced due to reduced sample damage effects by constantly replenishing the sample. This allows the study of sensitive samples that can only be produced in low concentrations. Our setup consists of a controlled sample environment that can be either under vacuum or an exchange gas, which allows the study of samples that are unstable in air. Finally, by matching the effective source point of the Raman instrument with the diameter of the jet, controlled experiments using laser beams of different wavelengths are possible. We see future applications of our setup for resonance Raman and time-resolved Raman measurements of bioinorganic samples.

Enhanced photoemission from laser-excited plasmonic nano-objects in periodic arrays

The process of photoelectron emission from gold surfaces covered with nano-objects that are organized in the form of a periodic array is addressed in the short laser pulse regime ( fs) at moderate intensities W cm−2 and for various laser wavelengths. The emission spectrum from a gold single crystal measured under the same conditions is used for reference. The comparison of the photo-emission yield and the energy of the ejected electrons with their counterparts from the (more simple) reference system shows that the periodic conditions imposed on the target surface drastically enhance both quantities. In addition to the standard mechanism of Coulomb explosion, a second mechanism comes into play, driven by surface plasmon excitation. This can be clearly demonstrated by varying the laser wavelength. This interpretation of the experimental data is supported by predictions from model calculations that account both for the primary quantum electron emission and for the subsequent surface-plasmon-driven acceleration in the vacuum. Despite the fact that the incident laser intensity is as low as W cm−2, such a structured target permits generating electrons with energies as high as 300 eV. Experiments with two incident laser beams of different wavelengths with an adjustable delay, have also been carried out. The results show that there exist various channels for the decay of the photo-emission signal, depending on the target type. These observations are shedding light on the various relaxation mechanisms that take place on different timescales.

Widely tunable two-colour seeded free-electron laser source for resonant-pump resonant-probe magnetic scattering.

The advent of free-electron laser (FEL) sources delivering two synchronized pulses of different wavelengths (or colours) has made available a whole range of novel pump–probe experiments. This communication describes a major step forward using a new configuration of the FERMI FEL-seeded source to deliver two pulses with different wavelengths, each tunable independently over a broad spectral range with adjustable time delay. The FEL scheme makes use of two seed laser beams of different wavelengths and of a split radiator section to generate two extreme ultraviolet pulses from distinct portions of the same electron bunch. The tunability range of this new two-colour source meets the requirements of double-resonant FEL pump/FEL probe time-resolved studies. We demonstrate its performance in a proof-of-principle magnetic scattering experiment in Fe–Ni compounds, by tuning the FEL wavelengths to the Fe and Ni 3p resonances.

Diffraction patterns with mth order symmetry generated by sectional spiral phase plates

The possibility of generating diffraction patterns with mth order symmetry when laser beams of different wavelengths illuminate sectional spiral phase plates (SPPs) is investigated analytically, numerically and experimentally. Such distributions are generated by a SPP with m sections in which the phase increases from 0 to 2π for the base wavelength. If the wavelength of laser light is changed, we get a decomposition of the mth order vortex beam into m off-axis vortices of the first order. We show that generating array of first-order optical vortices by the sectional SPPs can be dynamically controlled by the laser wavelength. Numerical simulation and experimental results are in a good agreement with the analytical calculations.

Contribution to the benchmark for ternary mixtures: Measurement of diffusion and Soret coefficients in 1,2,3,4-tetrahydronaphthalene, isobutylbenzene, and dodecane onboard the ISS.

The paper is devoted to processing the data of DCMIX 1 space experiment. In this experiment, the Optical digital interferometry was used to measure the diffusion and Soret coefficients in the ternary mixture of 1,2,3,4-tetrahydronaphthalene, isobutylbenzene and n-dodecane at mass fractions of 0.8/0.1/0.1 and at 25°C. The raw interferometric images were processed to obtain the temporal and spatial evolution of refractive indices for two laser beams of different wavelengths. The method for extracting the diffusion and thermal diffusion coefficients originally developed for optical beam deflection was extended to optical digital interferometry allowing for the spatial variation of refractive index along the diffusion path. The method was validated and applied to processing the data for Soret and diffusion steps in 5 experimental runs. The obtained results for the Soret coefficients and one of the eigenvalues of diffusion matrix showed acceptable agreement within each step. The second eigenvalue was not determined with sufficient accuracy.

Multi-wavelength holography with a single spatial light modulator for ultracold atom experiments.

We demonstrate a method to independently and arbitrarily tailor the spatial profile of light of multiple wavelengths and we show possible applications to ultracold atoms experiments. A single spatial light modulator is programmed to create a pattern containing multiple spatially separated structures in the Fourier plane when illuminated with a single wavelength. When the modulator is illuminated with overlapped laser beams of different wavelengths, the position of the structures is wavelength-dependent. Hence, by designing their separations appropriately, a desired overlap of different structures at different wavelengths is obtained. We employ regional phase calculation algorithms and demonstrate several possible experimental scenarios by generating light patterns with 670 nm, 780 nm and 1064 nm laser light which are accurate to the level of a few percent. This technique is easily integrated into cold atom experiments, requiring little optical access.

A method of step height measurement within the unambiguous range of two laser wavelengths interferometer

When two laser beams of different wavelength are simultaneously applied to a Michelson interferometer, a moiré of parallel patterns appears due to the difference in optical path length between the reference beam and the measuring beam. The pattern appears with a wavelength of λaλb/|λa−λb|, and the distance between the zeroes of the envelope is also λaλb/|λa−λb|. Using the moiré of parallel patterns, unambiguous range of step height is half of λaλb/|λa−λb|. However, intensity varies with an average wavelength of λaλb/(λa+λb), and intensity variation differs between the zeroes of each envelope. The unambiguous range is several times wider than λaλb/|λa−λb|. Intensity variation over the unambiguous range is measured, and coincides with calculated intensity variation, step height can be measured.

Polymer–inorganic nano-composite thin film upconversion light emitters prepared by double-beam matrix assisted pulsed laser evaporation (DB-MAPLE) method

The work was to investigate the possibility of making polymer–inorganic nano-composite films with upconversion fluorescence properties using the double beam matrix-assisted pulsed laser evaporation (DB-MAPLE) method. The existing pulsed laser deposition vacuum chamber was modified to accommodate two laser beams of different wavelengths for simultaneous ablation of two separate targets: a polymer host and a rare earth containing rare earth ion enriched upconversion fluoride dopant. The polymer target was prepared in chlorobenzene and kept frozen during the ablation with circulating liquid nitrogen in accordance with the MAPLE procedure. It was ablated with 1064nm beam from a pulsed Nd:YAG laser. The pellets made of the synthesized powders of inorganic phosphors of NaYF4:Yb3+, Er3+ and NaYF4:Yb3+, Ho3+were ablated with 532-nm beam from the same laser. The plumes from both targets were kept overlapping on the substrate during the deposition. X-ray diffraction analysis revealed that the most favorable for upconversion emission of the inorganic target materials was the hexagonal, beta phase of the NaYF4 matrix existing at a baking temperature between 400 and 600°C. The fabricated nano-composite films were characterized using scanning electron microscopy (SEM), atomic force microscopy (AFM), transmission electron microscopy (TEM) and optical fluorescence spectroscopy. The polymer nano-composite films generally retained the crystalline structure and the upconversion fluorescence properties of the initial rare earth compounds due to better control of the deposition process of the materials with substantially different properties. The proposed method can be potentially used for making a wide variety of nano-composite films.

Real-Time Viscosity and Mass Density Sensors Requiring Microliter Sample Volume Based on Nanomechanical Resonators

A microcantilever based method for fluid viscosity and mass density measurements with high temporal resolution and microliter sample consumption is presented. Nanomechanical cantilever vibration is driven by photothermal excitation and detected by an optical beam deflection system using two laser beams of different wavelengths. The theoretical framework relating cantilever response to the viscosity and mass density of the surrounding fluid was extended to consider higher flexural modes vibrating at high Reynolds numbers. The performance of the developed sensor and extended theory was validated over a viscosity range of 1-20 mPa·s and a corresponding mass density range of 998-1176 kg/m(3) using reference fluids. Separating sample plugs from the carrier fluid by a two-phase configuration in combination with a microfluidic flow cell, allowed samples of 5 μL to be sequentially measured under continuous flow, opening the method to fast and reliable screening applications. To demonstrate the study of dynamic processes, the viscosity and mass density changes occurring during the free radical polymerization of acrylamide were monitored and compared to published data. Shear-thinning was observed in the viscosity data at higher flexural modes, which vibrate at elevated frequencies. Rheokinetic models allowed the monomer-to-polymer conversion to be tracked in spite of the shear-thinning behavior, and could be applied to study the kinetics of unknown processes.

Double beam pulsed laser deposition of composite films of poly(methyl methacrylate) and rare earth fluoride upconversion phosphors

The objective of the work is to demonstrate feasibility of producing functional polymer nanocomposite films for light emitting applications using the new double beam pulsed laser deposition (DPLD) technique. The existing pulsed laser deposition vacuum chamber has been modified to accommodate two laser beams of different wavelengths for the in situ ablation of two targets: a polymer host and a rare earth based highly efficient upconversion emitting inorganic dopant. Special provisions were made for cooling the target to control the ablation of the polymer without interrupting the process. Nanocomposite films of acrylic polymer and nanoparticles of the compounds of the rare earth elements were fabricated by the proposed method with near-infra-red laser radiation (1064-nm wavelength) ablating the polymer targets and visible radiation (532nm) ablating the inorganic targets. The fabricated nanocomposite films were characterized using atomic force microscopy, X-ray diffraction, optical fluorescence spectroscopy, and visual observation of the fluorescence. It was discovered that the produced polymer nanocomposite films retained the crystalline structure and the upconversion fluorescence properties of the initial rare earth compounds mainly due to the better control of the deposition process of the materials with substantially different properties. The proposed method can be potentially used for making a wide variety of composite films.

Responses of Thin Film Photovoltaic Cell to Irradiation under Double Laser Beams of Different Wavelength

During the process of Laser beam long-range energy transmission based on the photovoltaic principle, the temperature elevation of the photovoltaic cell under Laser irradiation would greatly affect its photoelectric conversion efficiency. In this work, the heat generation mechanism of thin-film photovoltaic cell under Laser irradiation was analyzed based on the energy conversion relationship between light, electricity and heat. The output voltage characteristic of a thin film GaInP/GaAs/Ge triple-junction photovoltaic cell under irradiation of dual-wavelength Laser beam was investigated, and the results show the dependence of the conversion efficiency on the temperature and the valve effect, which was caused by the long wavelength Laser and would sharply reduce the photovoltaic conversion efficiency of short wavelength Laser. The temperature field of the multi-layer structure subjected to Laser irradiation was analyzed by finite element method, and the results indicate that the temperature elevation pattern depends on the spatial distribution of the light absorption and can be adjusted via optimizing the photovoltaic cell structure.

High-photosensitive resin for super-resolution direct-laser-writing based on photoinhibited polymerization

An ethoxylated bis-phenol-A dimethacrylate based photoresin BPE-100 of relatively high photosensitivity and modulus is used for the creation of sub-50 nm features. This is achieved by using the direct laser writing technique based on the single-photon photoinhibited polymerization. The super-resolution feature is realized by overlapping two laser beams of different wavelengths to enable the wavelength-controlled activation of photoinitiating and photoinhibiting processes in the polymerization. The increased photosensitivity of the photoresin promotes a fast curing speed and enhances the photopolymerization efficiency. Using the photoresin BPE-100, we achieve 40 nm dots for the first time in the super-resolution fabrication technique based on the photoinhibited polymerization, and a minimum linewidth of 130 nm. The influence of the power of the inhibiting laser and the exposure time on the feature size is studied and the results agree well with the prediction obtained from a simulation based on a non-steady-state kinetic model.

Influence of a yellow-tinted intraocular lens on laser beam transmittance

To compare the transmittance of laser beams that are used for photocoagulation through a yellow-tinted intraocular lens (IOL) and a clear IOL. The transmittance of laser beams of different wavelengths (488 + 514, 514, 521, 568 and 647 nm) through yellow-tinted and clear IOLs of varying dioptric powers [+10, +20 and +30 dioptres (D)] was measured using a laser power meter. The transmittance ratio was defined as the ratio of the transmittance thorough a tinted IOL to that through a clear IOL, assuming that the transmittance value of the latter is 1; this ratio was calculated for each IOL and each wavelength of the laser beam. There were no apparent differences in the transmittance values between the tinted and clear IOLs when the 521, 568 and 647 nm wavelengths were used. In contrast, the transmittance ratio decreased for the tinted IOL when the short wavelengths - 488 + 514 and 514 nm - were used, especially when an IOL of a higher dioptric power was used. This ratio was found to be 91.9% for a +10 D, 86.7% for a +20 D and 82.2% for a +30 D lens when a 488 + 514 nm wavelength beam was used. When treating patients using photocoagulation, we must bear in mind the decreased transmittance ratio of short-wavelength laser beams when passed through tinted IOLs and increase the setting power of the beam accordingly.

Study of the long-term behavior of the sensitivity of amorphous silicon photo detectors under illumination

The deterioration of the sensitivity of amorphous silicon strip photo detectors (‘ALMY’ sensors) under long-term illumination has been studied with collimated laser beams of different wavelengths and intensities. The high position sensitivity of the ALMY sensors allows for the precise localization of the illumination point and for monitoring of the local sensitivity degradation with respect to the rest of the non-illuminated sensor area.

Lap welding characteristics of thin sheet metals with combined laser beams of different wavelength

It is well known that arc welding of thin metallic sheets in difficult due to their easier distortion and deformation. On the other hand, in laser welding, such distortion and deformation is greatly reduced due to a smaller spot size and smaller heat input than in arc welding. Even in laser welding, thinner metallic sheets become more difficult to weld due to the loss of materials and the difficulty in supporting a shallow molten pool against evaporation and recoil pressure, leading to the formation of cut or drilled welds. In this study, therefore, lap welding characteristics of thin metallic sheets were investigated by utilizing combined beams or respective single beam of normal pulsed YAG laser and Q-switched SHG YAG laser. It was consequently found that the formation conditions for good lap welds in thin stainless steel sheets were broadened by using combined laser beams. Especially, lap welding of pure copper sheets was very difficult with single pulsed YAG laser; however, it was confirmed to be possible to weld them with combined laser beams of two different wavelengths in the air environment.