He-Ne Laser Beam Research Articles

Tunable effective nonlinear refractive index of graphene dispersions during the distortion of spatial self-phase modulation

Spatial self-phase modulation (SSPM) was observed directly when a focused He-Ne laser beam at 633 nm went through liquid-phase-exfoliated graphene dispersions. The diffraction pattern of SSPM was found to be distorted rapidly right after the incident beam horizontally passing through the dispersions, while no distortion for the vertically incident geometry. We show that the distortion is originated mainly from the non-axis-symmetrical thermal convections of the graphene nanosheets induced by laser heating, and the relative change of nonlinear refractive index can be determined by the ratio of the distortion angle to the half-cone angle. Therefore, the effective nonlinear refractive index of graphene dispersions can be tuned by changing the incident intensity and the temperature of the dispersions.

Transient Optical Phenomenon in Ferrofluids

In this paper, we report the experimental observation of diffraction patterns in a ferrofluid comprising of Fe3O4 nanoparticles in hexane by a 10 mW He-Ne laser beam. An external dc magnetic field (∼1.7kG) was applied perpendicular to the beam. Transient phenomenon in diffraction patterns is studied with and without magnetic field. Diffraction patterns showed a variation in both zero and applied magnetic field. This provides some information of non-linear optical properties and magneto-optical effects. Laser beam passed through a sample establishes refractive index gradient modifying the original Gaussian beam of the laser. Analysis of transient diffraction patterns can be used to study the parameters of ferrofluid like viscosity and thermal conductivity. This gives a new insight to understand the dynamics of the magnetic fluid and its potential use for the development of ferrofluid based sensors.

Study of optical parameters of two fluorinated isothiocyanato nematic liquid crystals exhibiting high birefringence

AbstractOptical studies have been carried out on two fluorinated isothiocyanato nematic liquid crystal (LC) compounds 4′-butylcyclohexyl-3, 5-difluoro-4-isothiocyanatobiphenyl and 4′-pentylcyclohexyl-3, 5-difluoro-4-isothiocynatobiphenyl. Transition temperatures of the two samples were confirmed using a polarizing microscope. The two LC compounds were found to exhibit fairly high clearing temperatures. Measurements of refractive indices of the two compounds were done by using thin prism method with He-Ne laser beam of wavelength 630 nm. Birefringence of the two LC compounds was calculated from the measured refractive indices. Both the compounds are found to display fairly high values of birefringence. Validation of a modified four-parameter model, based on Vuks equation describing the temperature dependence of refractive indices of the two liquid crystals, is also presented in this paper. The model is validated by fitting the experimentally measured values of refractive indices, birefringence and average refractive indices of the two nematic LCs with the theoretical values. In this paper, the calculation of order parameters of the LCs is presented by using two methods: direct extrapolation method based solely on the birefringence data and by using modified Vuks method based on Haller’s extrapolation. As observed from the obtained results, this procedure of calculating order parameter gives very reasonable results.

Surface Defect Detection for Some Ghanaian Textile Fabrics using Moire Interferometry

This analysis focused on using Moire Interferometry method to measure surface defects in woven fabrics. A laser imaging system based on moire Interferometry has been used as a tool for surface defect inspection of static textile fabric. Test textile fabrics samples with five different types of defects (hole, oil stains, warp-lacking, weft-lacking and dirt) were used. With the sample sand witched between two Ronchi rulings and illuminated by an expanded HeNe laser beam to form Moire configuration. The images from the fabric were acquired with a high resolution CCD camera. The recorded images were transferred to a computer for analysis by the image pro plus 5.0 software. By making use of image processing and FFT techniques, the surface defects such as lack of yarns and oil stains were analysed and detected. During the process of inspection and defect identification, it was observed that the three parameters, textual structure, the shape and size of the defect varied. In this paper, moire based technique for defect detection is presented. The result of the inspection of the textile fabric on the textile images revealed that FFT analysis serves as a filter in identifying such defects. Also, the fabric texture densities limited the intensity of the laser beam transmission through some fabrics. However, the variation of such intensities helped to deduce that the area covered with stain scatter most of the incident light and the more localised the defect the more the spread out of its transform. It explained the behaviour of the frequency spectrum of each sample and the smaller the width of the yarn spacing, the broader the entire diffraction pattern.

Gaussian beam radius measurement with a knife-edge: a polynomial approximation to the inverse error function

A method for approximating the inverse error function involved in the determination of the radius of a Gaussian beam is proposed. It is based on a polynomial inversion that can be developed to any desired degree, according to an a priori defined error budget. Analytic expressions are obtained and used to determine the radius of a TEM(oo) He-Ne laser beam from intensity measurements experimentally obtained by using the knife edge method. The error and the interval of validity of the approximation are determined for polynomials of different degrees. The analysis of the theoretical and experimental errors is also presented.

Random lasing and weak localization of light in transparent Nd+3 doped phosphate glass

Random lasing action and weak localization of light were observed in multiple visible wavelengths with highly transparent, Nd+3 doped phosphate glass gain media, with strong energy redistribution between different frequencies under different pumping powers. A tentative model based on photoinduced scattering was proposed and verified with a He-Ne laser beam in probing the lasing zone. The remarkable coherency and intensity changes of the probing laser beam confirmed the local, random scattering behind the photoinduced random lasing and the localization of light.

Hill-climbing algorithm based on Zernike modes for wavefront sensorless adaptive optics

To solve the local optimum problem, a modified hill-climbing algorithm based on Zernike modes is presented for wavefront sensorless adaptive optics. This algorithm adopts the Zernike mode coefficients, instead of the actuators' voltages in a traditional hill-climbing algorithm, as the adjustable variables to optimize the object function. First, the prin- ciple of the algorithm is described. Then the efficiency of the modified and traditional hill-climbing algorithms are analyzed numerically and experi- mentally using a He-Ne laser beam shaping system with a 37-element unimorph deformable mirror. The results of both simulations and experi- ments demonstrate that the modified hill-climbing algorithm can eliminate the local optimum problem with a fast speed of about 100 iterations. © 2013 Society of Photo-Optical Instrumentation Engineers (SPIE). (DOI: 10.1117/1.OE.52.1.016601) Subject terms: wavefront sensorless; adaptive optics; hill-climbing algorithm; Zernike modes; deformable mirror.

Apparatus to measure adsorption of condensable solvents on technical surfaces by photothermal deflection

This article describes an instrument for the measurement of the mirage effect as a tool to determine the molar adsorption per unit surface area Y(1) of condensable solvents in the presence of a non-condensable carrier gas. The present apparatus is a much improved version of previous prototypes developed in our laboratory and elsewhere with a higher surface bake-out temperature (150 °C rather than 40 °C), lower residual vacuum (3 Pa versus 100 Pa), greater sample surface (40 mm diameter instead of 10 mm), more powerful optical pump beam (150 W cf. 50 W), and larger saturated vapour preparation volume (4 L instead of 1 L). The new set-up also includes the in situ monitoring of the surface via a reflected HeNe laser beam for the real-time detection of the onset of condensation. Here, we give a detailed description of the various components, outline the experimental procedure, show typical results, and suggest some straightforward improvements.

Time-resolved measurements of shock-induced cavitation bubbles in liquids

A novel experimental method for the measurement of cavitation bubble dynamics is presented. The method makes use of a collimated cw HeNe laser beam that is focused onto a photodiode. A cavitation bubble centered in the laser beam leads to refraction and thus changes the diode signal. With sufficient temporal resolution of the measurement, the evolution of the bubble dynamics, and in particular, the collapse, could be well resolved (limitation is only due to diode response and oscilloscope bandwidth). In the present work this is demonstrated with cavitation bubbles generated with high-power nanosecond and femtosecond laser pulses, respectively. Bubble evolution is studied in two different liquids (water and glycerine) and at different temperatures and pressures.

反射式液晶空间光调制器电控光束偏转

An electro-controllable spatial light modulator of 8 m spatial resolution was employed to deflect the 632 nm He-Ne laser beam to high steering angle. The phase shift characteristic of the modulator related to the applied gray level was measured by co-focal interferometry and the maximum phase shift is 3 . According to the principle of binary optics, Different phase models were designed to deflect the incident laser beam. The incident laser beam can be deflected by 10 mrad apart from the incident laser when the phase level is eight, and the diffraction efficiency is high as 46%. The experimental and numerical results indicate that beam deflection with large angle can be achieved by employing the reflective liquid crystal phase-mode spatial light modulator, and the diffraction efficiency is mainly limited by the fill factor and the fly-back region in the liquid crystal cell.

Note: High capacity digital laser beam steering system

The combination of liquid crystal cells with polarizing cube beam splitters has been used to direct a beam of light to multiple directions. The polarization at each beam splitter is controlled by applying a signal to a corresponding liquid crystal cell. Ten cascaded stages have deflected a HeNe laser beam to 1024 digitally selectable angles.

Intensity based surface plasmon resonance sensor using a nanohole rectangular array

We show high resolution measurements of a surface plasmon resonance (SPR) sensor based on a rectangular nanohole array in a metal film. This SPR setup uses balanced intensity detection between two orthogonal polarizations of a He-Ne laser beam, which allows for sensitivity improvement, noise reduction and rejection of any uncorrelated variation in the intensity signal. A bulk sensitivity resolution of 6.4 x 10(-6) RIU is demonstrated. The proposed methodology is promising for applications in portable nanoplasmonic multisensing and imaging.

Integrated silicon-based nanoplasmonic sensor

The concept of an integrated nanoplasmonic sensor implemented on a silicon substrate is presented. Developed experimental setup based on rotation of linearly polarized light provides intensity detection between two orthogonal polarizations of a He-Ne laser beam. This optical configuration yields to a sensitivity improvement and noise reduction, resulting in a resolution of 4x10(-5) Refractive Index Units. Proposed methodology is promising for the application in portable nanoplasmonic multisensing and imaging.

Real-Time Optical Information Processing Through the Use of Low-Saturable Absorption in Bacteriorhodopsin Films

We have shown that the mechanism for a reversible anisotropic photoselection of bacteriorhodopsin (BR) molecules and a very small saturation intensity of a BR film allow for the blocking of any intensity feature from an image by just varying the intensity of a He-Ne laser beam without conventional frequency filters or rotation of an analyzer. It is found that the E204Q variant of BR offers additional valuable features. The photochemical cycle with a red-light absorbing O intermediate, B→M→O→B, and a distortion of the grating profile due to the low-saturation absorption are responsible for a large initial peak sharpness of the dynamic holographic recording kinetics.

Favourable outcome after cataract surgery with IOL implantation in uveitis associated with juvenile idiopathic arthritis

Management of uveitic cataract in patients with juvenile idiopathic arthritis (JIA) is challenging, and intraocular lens (IOL) implantation is controversial. This study investigated the outcome after minimally invasive surgery with IOL implantation. Retrospective analysis after phacoemulsification with in-the-bag IOL implantation was performed in 16 patients (17 operations) with ANA-positive JIA-associated chronic uveitis. In these patients, 25 G capsulectomy and anterior vitrectomy was performed and they received an intravitreal triamcinolone (TA) injection. Mean age at uveitis onset was 5 ± 2 years, and surgery was performed at a mean age of 11 ± 2.2 years. Preoperatively, uveitis was inactive in all patients, and visual acuity was logMAR 0.8 ± 0.44; additional uveitis complications were present in all patients, and 15 patients were receiving systemic immunosuppression/biologicals. After surgery (mean follow-up 26.5 ± 11.7 months), presence of cystoid macular oedema, papilloedema, ocular hypertension/glaucoma and hypotony did not increase compared with baseline. There was no significant worsening of AC inflammation (by cell numbers and laser flare values). IOL deposits persisted in four patients, and synechiae developed in eight. The visual acuity was improved (≥2 lines) in all patients (mean logMAR 0.3 ± 0.24). Retrolental membrane formation was not noted. Secondary capsular opacification was observed in seven patients, requiring Nd:YAG capsulotomy in five of them. Phacoemulsification and in-the-bag IOL implantation may improve visual outcome in JIA-associated uveitis with minimally invasive surgical technique and intravitreal TA injection. Well-controlled uveitis with appropriate use of topical steroids and systemic immunosuppression or biologicals appears as a perioperative requirement.

透射型体布拉格光栅对畸变激光束的空间滤波研究

Using transmitting volume Bragg gratings (TVBG) as a basis, an experiment on one-dimensional spatial filtering of a deformed laser beam is designed. The deformed laser beam results from a He-Ne laser beam modulated by an amplitude modulation plate with a spatial frequency of 7.2 mm ?1. Results show that when the central wave vector of the deformed beam satisfies the Bragg law of TVBG, the spatial profile of the -1st forward-diffracted order is similar to that of the undeformed He-Ne laser beam due to the TVBG with a spatial frequency selective bandwidth of less than 5.0 mm?1. The higher frequency components of the deformed beam are filtered out in the optical near field. Thus, the TVBG cleanup of the spatiallydeformed laser beam is realized experimentally.

Experiment Study of Influence on Laser Beam Quality Induced by Thermal Lens Effect and Depolarization Effect

For high power and repetitive Nd:Glass laser, there would appear serious thermal effect due to the significantly-enhanced pumping optical power density in laser rod, which would induce thermal double refraction, phase distortion, thermal focusing, thermal depolarization, etc. Thus, the laser output power and beam quality would be influenced severely. Influence of thermal lens effect and depolarization effect caused by thermal stress double refraction on laser beam were studied in this paper for high power and repetitive laser. In the experiment of thermal lens effect, change of the laser spot by thermal lens effect was recorded after a TEM00 He-Ne laser beam passing through the Nd:Glass rod pumped by Xe lamp, and the corresponding optical compensator was applied to eliminate the thermal lens effect to improve the beam quality. Configuration of polarizer was designed in our experiment to research the depolarization effect caused by thermal stress double refraction. First, emergent light distribution and loss factor caused by double refraction was calculated according to the theoretical model. Then the exiting cone-shaped polarized light intensity distribution was obtained through the experiment. It could be obtained from the experiments that thermal lens effect and depolarization effect caused by thermal double refraction would reduce the output laser beam quality to varied extents. As the number of laser pulses increased, thermal effects began to emerge and the output laser energy apparently decreased; when the thermal effects steadied, the output energy would be tending towards stability.

Intensity correlation properties of high-order optical vortices passing through a rotating ground-glass plate

We study the intensity correlation properties of optical vortices passing through a rotating ground-glass (RGG) plate and compare them with those of the TEM(00) mode of an He-Ne laser beam passed through the same RGG. We have observed that the intensity correlation curves for optical vortices decrease much faster than the corresponding curve for a TEM(00) mode of the He-Ne laser. The rate of decay of the correlation increases with the increase of order of the vortices. Our experimentally observed results are supported by exact analytical results.

Preliminary investigations with a photodiode-based fan-beam optical CT scanner

An updated version of a prototype fan-beam optical computed tomography scanner is presented. The scanner uses a 0.83 mm diameter 543 nm HeNe laser beam with a 60° line-generating lens for fan creation. A pair of linear polarizers is used for light intensity control. A set of five 64-element photodiode arrays forms the detector arc. Extended dynamic range is achieved by adjusting light intensity and photodiode integration time. Two detector collimators (one single-slot, one multi-hole) are employed for comparative purposes. Highly attenuating solutions of scatter-based and absorption-based agents are examined using both types of collimation. Comparison of the results provides useful information about the persistent presence of scatter in optical CT.

Two-color CO2/HeNe laser interferometer for C-2 experiment

A six-channel two-color interferometer has been developed for plasma electron density measurements in the C-2 field reversed configuration experiment. A CO(2) laser is utilized as the main probe beams, while copropagating visible HeNe laser beams are mainly sensitive to vibration. Density measurements in C-2 plasmas have shown that this is a reliable turn-key system. The maximum residual phase noise after vibration compensation is less than ±5°, corresponding to a line integral density of 3×10(18) m(-2). The time resolution for routine operation is 2 μs.