He-Ne Laser Source Research Articles

Synthesis, crystal growth, structural, optical, and laser damage threshold characterizations on 2-amino-4,6-di­methyl­pyrimidinium hydrogen sulfate single crystal for nonlinear optical applications

2-Amino-4,6-di­methyl­pyrimidinium hydrogen sulfate (2AMPHS) organic single crystal was successfully grown by slow evaporation solution technique (SEST) for the first time. A good transparent 2AMPHS single crystal with dimensions of 5 mm × 5 mm × 2 mm was grown after a 25-day growth period. The 2AMPHS single crystals structural parameters were confirmed and well matched with the reported values. The good crystalline nature of 2AMPHS crystal was characterised using SXRD, PXRD, UV–Visible NIR, laser damage threshold, and third harmonic generation (THG). The optical property of 2AMPHS crystal was investigated by UV–visible-NIR analysis. Laser damage threshold analysis was performed with an Nd: YAG laser, and the laser wavelength is 1064 nm. The third harmonic generation study was analysed by a Z-scan study. The He-Ne laser source with a wavelength of 632.8 nm has used for Z-scan analysis.

Thermal Annealing Effects on the Raman and Photoluminescence Properties of Mono and Few-Layer MoS<sub>2</sub> Films

In this study, we report that the thermal treatment effects on the Raman and photoluminescence (PL) spectra of mono and few-layer MoS2 films by annealing in the vacuum and air at 300°C, respectively. The MoS2 film samples were prepared on silicon substrate by exfoliating from a bulk MoS2 crystal with a micromechanical exfoliation. For characterization of structural properties of the MoS2 films and identification of the Raman active modes, Raman spectrometer equipped with a He-Ne laser source and an optical microscope has been used. The results show that the vacuum annealing 7L MoS2 decreases the Full Width at Half Maximum (FWHM) of the Raman active modes as E12g, A1g and the vacuum annealing 1L MoS2 increases the PL intensity and peak energy, for 60% and 13.3meV, respectively also air annealing bilayer MoS2 increased the PL intensity (IA) and peak energy (EA), respectively for 85% and 15.4 meV (300°C for 40 min). After thermal annealing (vacuum and air), we observe that the indirect bandgap of the few-layer MoS2 was changed.

A GPS-Referenced Wavelength Standard for High-Precision Displacement Interferometry at λ = 633 nm.

Since the turn of the millennium, the development and commercial availability of optical frequency combs has led to a steadily increase of worldwide installed frequency combs and a growing interest in using them for industrial-related metrology applications. Especially, GPS-referenced frequency combs often serve as a "self-calibrating" length standard for laser wavelength calibration in many national metrology institutes with uncertainties better than u = 1 × 10-11. In this contribution, the application of a He-Ne laser source permanently disciplined to a GPS-referenced frequency comb for the interferometric measurements in a nanopositioning machine with a measuring volume of 200 mm × 200 mm × 25 mm (NPMM-200) is discussed. For this purpose, the frequency stability of the GPS-referenced comb is characterized by heterodyning with a diode laser referenced to an ultrastable cavity. Based on this comparison, an uncertainty of u = 9.2 × 10-12 (τ = 8 s, k = 2) for the GPS-referenced comb has been obtained. By stabilizing a tunable He-Ne source to a single comb line, the long-term frequency stability of the comb is transferred onto our gas lasers increasing their long-term stability by three orders of magnitude. Second, short-term fluctuations-related length measurement errors were reduced to a value that falls below the nominal resolving capabilities of our interferometers (ΔL/L = 2.9 × 10-11). Both measures make the influence of frequency distortions on the interferometric length measurement within the NPMM-200 negligible. Furthermore, this approach establishes a permanent link of interferometric length measurements to an atomic clock.

A New Non-linear Stilbazolium Derivative Crystal of 4-[2-(3 Methoxy-phenyl)-vinyl]-1-methyl-pyridinium+ Iodide− (MMPI): Analysis of Its Structural, Surface, Optical and NLO Properties

New organic stilbazolium family of 4-[2-(3 methoxy-phenyl)-vinyl]-1-methyl-pyridinium+ iodide− (MMPI) was successfully synthesized using the condensation reaction method. The recrystallization process was carried out to improve the purity of the synthesized material, and MMPI and grown into a single crystal by the solvent evaporation method. The solubility of the (MMPI) material was taken at different temperatures with a mixture of solvent Methanol: Acetonitrile (1:1). The grown MMPI crystal structure and cell parameters were solved via single crystal X-ray diffraction analysis. The structural formation of the title material was also confirmed by Nuclear Magnetic Resonance spectroscopic (NMR) studies. The experimental vibrational bands in the synthesized material have been assigned by Fourier Transform Infrared (FT-IR) spectrum analysis. From the optical analysis, the grown crystal’s lower cut-off wavelength, transmittance range, and optical band gap were calculated. Chemical etching analysis was carried out on the grown crystal surface (MMPI) to study the surface property of the grown MMPI crystal. Along with etching, atomic force microscope (AFM) and scanning electron microscope (SEM) were also used to analyses the grown MMPI crystal surface. Hirshfeld surface analysis was used to analyses the intermolecular interactions. HOMO and LUMO energies were calculated theoretically using the Gaussian View 6 programmer. The chemical activity was evaluated via the molecular electrostatic potential using the density functional theory (DFT) method. The third-order nonlinear optical parameters of the title crystal were evaluated at He-Ne laser (632.8 nm) source with the single beam Z-scan technique. In addition, it shows significant reverse saturable absorption and self-defocusing.

Measuring Laser Beam Transmission through Exposed/Etched CN-85 Detectors

Cellulose Nitrate (CN-85) plastic detectors, with a thickness of 100 μm, were exposed to radiation by alpha particles. Then, the irradiated detectors were etched and treated with radiation by using He-Ne laser source. The influence of laser irradiation on the physical characterization of CN-85 track detectors has been investigated through track radii. In this study, the tracks’ number and track radii were calculated. The results showed that the track radii of laser-etched CN-85 detectors were reduced with increasing the etching time. Further, the track radii were changed due to the effects of alpha particles on the CN-85 detectors. This method is found to be a relatively inexpensive, easy, and effective tool for measuring the radiation dose.

The magnetic switch manufacturing by using ferrofluid and ferrofluid doped copper nanoparticles

In this work, a magnetic switch was prepared using two typesof ferrofluid materials, the pure ferrofluid and ferrofluid doped with copper nanoparticles (10 nm). The critical magnetic field (Hc) and the state of magnetic saturation (Hs) were studied using three types of laser sources. The main parameters of the magnetic switch measured using pure ferrofluid and He-Ne Laser source were Hc(0.5 mv, 0.4 G), Hs (8.5 mv, 3 G). For the ferrofluid doped with copper nanoparticles were Hc (1 mv, 4 G), Hs (15 mv, 9.6 G), Using green semiconductor laser for the Pure ferrofluid were Hc (0.5 mv, 0.3 G) Hs (15 mv, 2.9 G). While the ferrofluid doped with copper nanoparticles were Hc (0.5 mv, 1 G), Hs (12 mv, 2.8 G) and by using the violet semiconductor laser the pure ferrofluid parameters were Hc(0.5 mv, 0.5 G), Hs (15 mv, 3.5 G) while the ferrofluid doped with coppernanoparticles are Hc (0.5 mv,1 G), Hs (15 mv, 3.3 G).

Laser induced fluorescence with 2-D Hilbert transform edge detection algorithm and 3D fluorescence images for white spot early recognition.

There is a must for non-invasive caries detection method to supplement traditional visual assessment by the clinician before lesion progression reaches a stage requiring invasive therapy. In this paper, the nature of tissue response to light interaction has been used for early diagnosis, using laser induced fluorescence spectroscopy. Human tooth sample was illuminated with He-Ne laser sources (633nm) with energy 5mW. The reflected and emitted spectra of investigated samples were collected using hyperspectral camera to develop multispectral images. The variation of reflected and emitted energy as function in wavelength was employed to generate characteristic spectrum of each tooth tissue. Human teeth caries lesion releases their excess energy by emitting fluorescence light producing chemical footprint signature for each tooth elements and caries state. This non-invasive, non-contact, and non-ionizing hyperspectral imaging system was employed to diagnose and classify different caries types and stages. Reconstructed 3D fluorescence images offered discrimination between enamel and dentin caries at 633nm illumination spectral line; white spot lesion was clearly detected and recognized at far visible and infrared wavelength ranges. This study reports on customized optical imaging system that can offer high sensitivity, high resolution. Optimum stimulating wavelength for early caries detection was reported to be 633nm. This novel approach can offer a full map of caries degree status.

Insight into the effect of screw dislocations and oxygen vacancy defects on the optical nonlinear refraction response in chemically grown ZnO/Al2O3 films

We report the effect of screw dislocations and oxygen vacancy defects on the optical nonlinear refraction response of ZnO films grown on a sapphire substrate at various oxygen flow rates using the chemical vapor deposition technique. The nonlinear refraction response was investigated in the off-resonant regime using a CW He-Ne laser source to examine the role of the intermediate bandgap states. It has been observed that the structural defects strongly influence the optical nonlinearity in the off-resonant regime. Nonlinearity has been found to improve as the oxygen flow rate is lowered from 2 sccm to 0.3 sccm. From photoluminescence studies, we observe that the enhanced defect density of the electronic defect levels due to the increased concentration of structural defects (with the decrease in the oxygen flow rate) is responsible for this improved optical nonlinearity along with the thermal effect. This suggests that defect engineering is an effective way to tailor the nonlinearity of ZnO films and their utility for optoelectronic device applications.

Real-time complex amplitude reconstruction method for beam quality M2 factor measurement.

We present a real-time complex amplitude reconstruction method for determining the beam propagation ratio M2 of laser beams based on the transport of intensity equation (TIE). In this work, a synchronous acquisition system consisting of two identical CCDs is established. Once two beam intensity images at different cross-section positions along the optical axis are captured simultaneously by the system, the complex amplitude of the laser beam can be rapidly reconstructed using TIE algorithm. Then the beam intensity distribution at any section position along its propagation direction can be obtained by using angular spectrum (AS) theory. The beam quality M2 factor is therefore calculated utilizing the second-order moments and hyperbola fitting methods, which conform to the ISO standard. The suitability of this method is verified by the numerical analysis and experiments with the He-Ne and high-power fiber laser sources, respectively. The experimental technique is simple and fast, which allows to investigate laser beams under conditions inaccessible to other methods.

Studies on the growth aspects, structural and third-order nonlinear optical properties of Piperidinium 3-carboxy-4-hydroxy benzenesulfonate single crystal

Organic nonlinear optical material Piperidinium 3-carboxy-4-hydroxy benzenesulfonate (PBS) single crystal was successfully grown by solution growth method. Single crystal X-ray diffraction study confirms that, the grown crystal belongs to P21/n space group. The crystalline quality of PBS was ascertained by HRXRD studies. Infrared spectral analysis showed the vibrational behaviour of chemical bonds and presence of its functional groups. TG/DTA studies were used to study the thermal stability and decomposition stages of the compound. UV–visible transmittance studies showed the transparency region, cut-off wavelength and band gap of the grown crystal. Photoluminescence emission study was carried out for the grown crystal to show its electronic properties. By using Nd:YAG laser, the laser damage threshold was estimated for the grown crystal. The third-order nonlinear optical parameters of the grown crystal were estimated by Z-scan technique using He-Ne laser source. The mechanical property of the PBS crystal was studied by using Vicker's microhardness measurement.

Laser vibration sensing at Fraunhofer IOSB: review and applications

Laser vibrometry based on coherent detection allows noncontact measurements of small-amplitude vibration characteristics of objects. This technique, commonly using the Doppler effect, offers high potential for short-range civil applications and for medium- or long-range applications in defense and security. Most commercially available laser Doppler vibrometers are for short ranges (up to a few tens of meters) and use a single beam from a low-power HeNe laser source (λ=633 nm). Medium- or long-range applications need higher laser output power, and thus, appropriate vibrometers typically operate at 1.5, 2, or 10.6 μm to meet the laser safety regulations. Spatially resolved vibrational information can be obtained from an object by using scanning laser vibrometers. To reduce measuring time and to measure transient object movements and vibrational mode structures of objects, several approaches to multibeam laser Doppler vibrometry have been developed, and some of them are already commercially available for short ranges. We focus on applications in the field of defense and security, such as target classification and identification, including camouflaged or partly concealed targets, and the detection of buried land mines. Examples of civil medium-range applications are also given.

Effect of oxygen partial pressure on the structural and optical properties of ion beam sputtered TiO2 thin films

We report the effect of oxygen partial pressure on the structural, electronic and nonlinear optical properties of ion beam sputtered TiO2 thin films deposited on glass substrate at 40% of oxygen (S1) and 20% of oxygen (S2) partial pressure. XRD data shows the crystalline nature of S1 film while the film S2 was amorphous in nature. The energy band gap of the thin films calculated from their UV-Vis spectra was found to be 3.63 eV (S1) and 3.56 eV (S2). The decrease in the band gap with decrease in oxygen partial pressure may be attributed to the amorphous nature of the film. The nonlinear refractive indices for both the films were obtained from the closed aperture Z-scan experiment performed using a cw He-Ne laser source operating at 632.8 nm and were found to be 17.6×10-9 m2/W and -5.64×10-9 m2/W for S1and S2 films, respectively. The reversal in the sign of the nonlinear refractive index may also be ascribed to the crystallinity of the grown films.

Measurement of the residual wedge angle of a nontransparent parallel plate with a modified cyclic path optical configuration.

A new technique for the measurement of the residual wedge angle (RWA) of a nontransparent nearly parallel plate (NPP), using a polarized He-Ne laser source, is proposed. A modified cyclic path optical configuration is used to produce counterpropagating collimated beams, which get reflected from the end surfaces of the NPP and are combined to produce two-beam Fizeau fringes, whose spacing is inversely proportional to the wedge angle of the NPP. The states of polarization of the beams reflected from the end surfaces of the NPP are transformed to opposite circular polarizations, and polarization phase shifts are applied between them. Phase shifting interferometry (PSI) has been used to determine the angular tilt between the interfering beams and, hence, the RWA of the NPP. Results obtained from a validation experiment are presented. The PSI-based technique does not suffer from any measurement ambiguities due to limitations in effective beam aperture.

Light depolarization in off-specular reflection on submicro rough metal surfaces with imperfectly random roughness.

Depolarization at a rough surface relates to its roughness and irregularity (e.g., sags and crests) besides the material property. However, there is still lack of general theory to clearly describe the relationship between depolarization ratios and surface conditions, and one important reason is that the mechanism of depolarization relates to geometric parameters such as microcosmic height/particle distributions of sub-micro to nm levels. To study the mechanism in more detail, a compact laser instrument is developed, and depolarization information of a linearly polarized incident light is used for analyzing the roughness, during which a He-Ne laser source (λ = 632.8 nm) is used. Three nickel specimens with RMS roughness (Rq) less than λ/4 are fabricated and tested. Six different areas in each specimen are characterized in detail using an AFM. Rq are in the range of 34.1-155.0 nm, and the heights are non-Gaussian distribution in the first specimen and near-Gaussian distribution in the others. Off-specular inspection is carried out exactly on these 18 characterized areas, and results show that the cross-polarization ratios match quite well with Rq values of the first sample that has Rq ≤ λ/10 (or Rt ≤ λ), while they match well with maximum height, Rt, values of the other two that have Rt > λ (the maximum derivation is 11%). In addition, since this instrument is simple, portable, stable, and low-cost, it has great potential for practical online roughness testing after a linear calibration.

Studies on the growth, structural, spectral and third-order nonlinear optical properties of Ammonium 3-carboxy-4-hydroxy benzenesulfonate monohydrate single crystal

An organic nonlinear optical bulk single crystal, Ammonium 3-carboxy-4-hydroxy benzenesulfonate monohydrate (ACHBS) was successfully grown by solution growth technique. Single crystal X-ray diffraction study confirms that, the grown crystal belongs to P21/c space group. Powder X-ray diffraction and high resolution X-ray diffraction analyses revealed the crystallinity of the grown crystal. Infrared spectral analysis showed the vibrational behavior of chemical bonds and its functional groups. The thermal stability and decomposition stages of the grown crystal were studied by TG-DTA analysis. UV–Visible transmittance studies showed the transparency region and cut-off wavelength of the grown crystal. The third-order nonlinear optical susceptibility of the grown crystal was estimated by Z-scan technique using HeNe laser source. The mechanical property of the grown crystal was studied by using Vicker’s microhardness test.

Measurement of Sound Speed in Liquid Using Optical Approach

An optical method to determine a speed of sound (or ultrasound) in water was described in this work. The measuring system composes of ultrasonic transducer, glass water bath, He-Ne laser source, lens, and screen. An ultrasound fog generator used for producing an ultrasound with a frequency f of 1.74 MHz was immersed in DI water. It was fixed at one side of water bath. When the sound wave travels in water along the length of water bath, a standing wave is obtained from the interference of the incidence wave and the wave reflected from the opposite side of water bath. The node and antinode of the standing wave act as an opaque and transparent medium. As a He-Ne laser beam with a wavelength of 632.8 nm travelled to a convex lens with a focal length of 5 cm and diverged through the sound field, an enlarged standing wave pattern was shown on a white screen. The wavelength of sound wave λ was obtained using geometry (similar triangle). Therefore, the speed of ultrasound in water was calculated by v = fλ. In this work, the water temperature was varied in a range of 15 - 39 °C. The results showed that the speed of sound increased with increasing the water temperature. The percentage error was below 2.8. This proposed method can be used for demonstrating physics principles such as waves and optics for high school students and undergraduates.

Microlens array fabricated by a low-cost grayscale lithography maskless system

This work presents the fabrication of a contiguous f/#=f/15 Fresnel microlens array (MLA) by employing a low-cost home-built maskless exposure lithographic system based on a digital light projector technology by using Texas Instruments’ digital micromirror device chip. A continuous diffractive phase relief structure was generated on a photoresist-coated silicon wafer, replicated in polydimethylsiloxane (PDMS) and electrostatically bonded to a glass substrate. The whole exposure time takes 10.8 min to expose a 2.4×2.4 mm MLA, with a resolution of 2.5 μm. This exposure time is relatively short, enabling high throughput or fast prototyping. Optical characterization was carried out using a He-Ne laser source (λ=633 nm ), by evaluating the maximum intensity of each spot generated at the MLA focal plane, Imax, as well as its sharpness by measuring their full width at half maximum (FWHM) intensity values. The resulting FWHM and maximum intensity spot average values were FWHM AVG =20±8% μm and Imax AVG =0.71±7% a.u. , respectively. The quality of replication was evaluated by profile characterization of the resulting mold and replica based on step height measurement along 180 μm. The maximum obtained difference was 32 nm, corresponding to 2.5% of the total mold height or λ/20 . AFM measurements were also carried out to quantify the roughness quality between mold and replica. The resulting RMS roughness was 4.73 nm (λ/130 ) and 6.66 nm (λ/95 ) for mold and replica, respectively. A comparison between theoretical and measured intensity profiles at the MLA focal plane was also carried out. A good correspondence between the results was found. Such an MLA can be applied as a Shack–Hartmann wavefront sensor in optical interconnects and to enhance the efficiency of detector arrays.

Design and Construction Optical Fiber Sensor System for Detection the Stress and Fine Motion

Two main concepts in design and construction of stress and fine motion detection system using fiber optic sensor was included in this project. The first is design and construction concept using Intensity Modulation techniques using plastic multimode optical fiber(125μm dim)and has N A (0.27) with losses rate (2.1 db)and directionality about(25 db),and we used (He-Ne)laser source(632.8 nm)with (LLM-2 light power meter) to detect the variation in output laser power due to micro-displacement for movement body under test. The second concept include Modeling for laser beam tracking through fiber and that which reflected for mirror to detector. Variation in output power due to target movement was theoretical analyzed from study of variation of Gaussian front wave profile of using (MATLAB) program within displacement range from(0-5 mm).Non-linear relation between separated distance and beam intensity was investigated. Finally our design are evaluated in comporizim with published research which found compatible in Theoretical and experimental results.

Design and Construction Optical Fiber Sensor System for Detection the Stress and Fine Motion

Two main concepts in design and construction of stress and fine motion detection system using fiber optic sensor was included in this project. The first is design and construction concept using Intensity Modulation techniques using plastic multimode optical fiber(125μm dim)and has N A (0.27) with losses rate (2.1 db)and directionality about(25 db),and we used (He-Ne)laser source(632.8 nm)with (LLM-2 light power meter) to detect the variation in output laser power due to micro-displacement for movement body under test. The second concept include Modeling for laser beam tracking through fiber and that which reflected for mirror to detector. Variation in output power due to target movement was theoretical analyzed from study of variation of Gaussian front wave profile of using (MATLAB) program within displacement range from(0-5 mm).Non-linear relation between separated distance and beam intensity was investigated. Finally our design are evaluated in comporizim with published research which found compatible in Theoretical and experimental results.

Large Area Metal Nanowire Arrays with Tunable Sub-20 nm Nanogaps

We report a new top-down nanofabrication technology to realize large area metal nanowire (m-NW) arrays with tunable sub-20 nm separation nanogaps without the use of chemical etching or milling of the metal layer. The m-NW array nanofabrication technology is based on a self-regulating metal deposition process that is facilitated by closely spaced and isolated heterogeneous template surfaces that confine the metal deposition into two dimensions, and therefore, electrically isolated parallel arrays of m-NW can be realized with uniform and controllable nanogaps. Au-NW and Ag-NW arrays are presented with high-density ~10(5) NWs cm(-1), variable NW diameters down to ~50 nm, variable nanogaps down to ~5 nm, and very large nanogap length density ~1 km cm(-2). The m-NW arrays are designed and implemented as interdigitated nanoelectrodes for electrochemical applications and as plasmonic substrates where the coupled-mode localized surface plasmon resonance (LSPR) wavelength in the nanogaps between adjacent m-NW dimers can be precisely tuned to match any excitation source in the range from 500 to 1000 nm, thus providing optimal local electromagnetic field enhancement. A spatially averaged (n = 2500) surface-enhanced Raman scattering (SERS) analytical enhancement factor of (1.2 ± 0.1) × 10(7) is demonstrated from a benzenethiol monolayer chemisorbed on a Au-NW array substrate with LSPR wavelength matched to a He-Ne laser source.