He-Ne Laser Beam Research Articles

Optically controlled transmission of porous polyethylene terephthalate films filled with nematic liquid crystal

We investigated the influence of blue light (lambda=450 nm) on the optical properties of porous polyethylene terephthalate (PET) films filled with a nematic liquid crystal (E7). In experiments, films of 12 microm thickness with randomly distributed open-end pores of well-defined diameters (170, 400, 850 nm) were studied. It was found that blue-light illumination of the porous PET films preliminarily treated by an azo dye solution resulted in strong intensity changes when the He-Ne laser beam passed through the sample. The observed effect can be attributed to the heating caused by the absorption of blue light by azo dye molecules.

S1904-1-2 アブレーション材料衝撃層内のレーザー光透過減衰計測実験(大気突入・減速技術(1),社会変革を技術で廻す機械工学)

Optical attenuation characteristics in the shock layer for carbonaceous material and Teflon heated in arc jet wind tunnel flows are examined. A He-Ne laser beam is passed ahead of a blunt body in a direction perpendicular to an arc jet flow and the temporal history of the intensity of the laser is measured. The results show that no optical attenuation is observed in arc jet freestream and in a shock layer for the case of Teflon. For the carbonaceous material, intermittent optical attenuation is observed when the laser beam is passed in and probably ahead of the shock layer. This behavior is believed to due to the particulate interference of the laser beam. The particles are likely ejected from the carbonaceous material due to spallation.

Comparison of Au and Pt Foils for an Imaging Bolometer

In the imaging bolometer a thin metal foil converts plasma radiated power to infrared radiation measured by an infrared camera. Calibration of the foil provides information on its sensitivity, which is helpful in selecting the best foil material. In this study thermal properties of submicron Au and Pt foils are investigated by heating the foils with a chopped HeNe laser beam (∼20 mW) and observing the temperature change, ΔT, and thermal time constant, τ, of the foil temperature. Assuming that the foil cooling is dominated by diffusion, we can compare the relative sensitivities of the foils by comparing the ratio of the thermal diffusivity to the thermal conductivity of the foil, κ/k, to the ratio ΔT/τ. The results indicate that Pt is more than 9 times more sensitive than Au even though standard thermal properties indicate that Au should be slightly (14%) more sensitive than Pt. This inconsistency indicates that the IR radiation is dominant over diffusion in the foil cooling. In that case the sensitivity should be evaluated by 1/k ∼ ΔT, which indicates that Pt is 8 times more sensitive than Au, while the ratio of thermal conductivities indicates that it should be only 4 times more sensitive.

REALIZATION OF HOLOGRAPHIC STORAGE ON METAL FILM BY FEMTOSECOND LASER PULSES MICROMACHINING

Optical information has been stored on the metal film by femtosecond laser pulses with the aid of the computer-generated hologram (CGH). The Fourier transform of an object is performed by a computer, and then the resulted complex amplitude distribution is encoded by the detour phase method. The resulted cell-oriented CGH is directly written on the metal film deposited on the glass substrate using femtosecond laser by selective ablation. The object wave has also been reconstructed with high fidelity by using a collimated He-Ne laser beam.

Measurement and analysis of reversible transformations of vortex-free and singular light fields produced by PDLC cells

In this work, we have firstly realized and investigated reversible transformations of vortex-free and singular optical complex landscapes appearing in a He-Ne laser beam transmitted through a PDLC cell, which is controlled by an applied DC voltage. Biaxes of all micro size LC domains are oriented approximately along the applied electric field, and vortex-free complex landscape exists at 200 V. At 160 V, biaxes orientation spreads, and the first 'embryo' of vortices in the form of a smooth phase step appears. The first vortex pair nucleates at 140 V. Multitude of vortex pairs is realized when electric field is switched off. Reversed evolution is realized when the applied DC voltage grows from zero value to 200 V. It was shown that the observed topological evolution is fully defined by changes in structure and localization of real and imaginary zero-intensity lines for output complex light field. The developed technique of parametric dynamics can be applied successfully to realize and investigate various types of controlled optical elements including media with nanoadditions.

External measurement of dihedral right angles with cyclic optical configuration

A new technique for external measurement of dihedral right angles is presented. An expanded, collimated, and linearly polarized He-Ne laser beam (632.8 nm) from a Fizeau interferometer is launched into a cyclic path optical configuration (CPOC) in which the counterpropagating p and s polarization components traverse the same optical path in opposite directions. A right-angled component (RAC), with its plane surfaces forming the right angle, is set to externally reflect the counterpropagating p and s components of the CPOC in nearly the same directions but with a lateral separation. In a plane normal to the right-angle edge of the RAC, the laterally separated collimated beams have angular separation, which is equal to twice the error in the dihedral right angle. Another CPOC setup is used to recombine the beams by reducing the lateral shear to zero. Error in right angle is calculated from the spacing of the resulting two-beam Fizeau fringes. Methods for overcoming the restriction of measurement accuracy due to beam aperture limitation and the effects of the positional tilt of the RAC have been discussed. Results of validation experiments are presented.

He–Ne laser (632.8 nm) pre‐irradiation gives protection against DNA damage induced by a near‐infrared trapping beam

We report the results of a study carried out to investigate the effect of He-Ne laser (632.8 nm) pre-irradiation on DNA damage induced by continuous wave 1064 nm trapping beam exposure in MCF-7 cells. A significant decrease in % tail DNA (p < 0.05) was observed in MCF-7 cells pre-exposed to He-Ne laser beam. The dependence of the induced protection against 1064 nm trapping beam irradiation induced DNA damage on the time interval between the two irradiations as well as the He-Ne laser pre-irradiation parameters is presented.

Effect of irradiation of LASER beam on polymer blends

Irradiation of He-Ne LASER beam on polystyrene (PS) and poly vinyl chloride (PVC) polyblend sample for different time intervals viz. 3, 5,7, 10 and 15 min. Structural and electrical properties have been studied before and after irradiation. It has been found that irradiation increases the dc electrical conductivity due to creation of new charge carriers in the polyblend sample.

Magnetic-field-induced optical anisotropy in ferrofluids: A time-dependent light-scattering investigation

We report an experimental investigation of time dependent anisotropic light scattering by an aqueous suspension of tetramethyl ammonium hydroxide coated Fe3O4 nanoparticles (approximately 6 nm) under the ON-OFF transient of an external dc magnetic field. The study employs the synchronized recording and measurement of the two magnetic-field-induced light-scattering patterns produced by two identical orthogonal He-Ne laser beams passing through the ferrofluid sample and propagating parallel and perpendicular to the applied field, respectively. From these patterns, we extract the time dependence of the induced optical anisotropy, which provides a measure of the characteristic time scale and kinematic response for field-induced structure formation in the sample. We propose that the time evolution of the scattering patterns, which is very fast at short times and significantly slower at long times, can be explained using a model based on a two-stage chain formation and coarsening processes.

Superposition of orbital angular momentum of photons by a combined computer-generated hologram fabricated in silica glass with femtosecond laser pulses

This paper introduces a novel method to realize the superposition of orbital angular momentum of photons by combined computer-generated hologram (CCGH) fabricated in silica glass with femtosecond laser pulses. Firstly, the two computer-generated holograms (CGH) of optical vortex were obtained and combined as a CCGH according to the design. Then the CCGH was directly written inside glass by femtosecond laser pulses induced microexplosion without any pre-or post-treatment of the material. The vortex beams with different vortex topological charges (including new topological charges) have been restructured using a collimated He-Ne laser beam incidence to the CCGH normally. A theoretical and experimental explanation has been presented for the generations of the new topological charges.

Optical temperature sensor and thermal expansion measurement using a femtosecond micromachined grating in 6H-SiC

An optical temperature sensor was created using a femtosecond micromachined diffraction grating inside transparent bulk 6H-SiC, and to the best of our knowledge, this is a novel technique of measuring temperature. Other methods of measuring temperature using fiber Bragg gratings have been devised by other groups such as Zhang and Kahrizi [in MEMS, NANO, and Smart Systems (IEEE, 2005)]. This temperature sensor was, to the best of our knowledge, also used for a novel method of measuring the linear and nonlinear coefficients of the thermal expansion of transparent and nontransparent materials by means of the grating first-order diffracted beam. Furthermore the coefficient of thermal expansion of 6H-SiC was measured using this new technique. A He-Ne laser beam was used with the SiC grating to produce a first-order diffracted beam where the change in deflection height was measured as a function of temperature. The grating was micromachined with a 20 microm spacing and has dimensions of approximately 500 microm x 500 microm (l x w) and is roughly 0.5 microm deep into the 6H-SiC bulk. A minimum temperature of 26.7 degrees C and a maximum temperature of 399 degrees C were measured, which gives a DeltaT of 372.3 degrees C. The sensitivity of the technique is DeltaT=5 degrees C. A maximum deflection angle of 1.81 degrees was measured in the first-order diffracted beam. The trend of the deflection with increasing temperature is a nonlinear polynomial of the second-order. This optical SiC thermal sensor has many high-temperature electronic applications such as aircraft turbine and gas tank monitoring for commercial and military applications.

Sci-Fri PM: Planning-08: Zero diffusion radiochromic genipin-gelatin dosimeter.

To develop a zero diffusion radiochromic hydrogel by cross-linking gelatin polymers with genipin, for three-dimensional (3-D) radiation dosimetry. Gelatin and genipin were dissolved in distilled water and continuously stirred at 40C for thee hours and then sulfuric acid was acid prior to placing gel in containers. Concentrations of genipin, gelatin and sulfuric acid were varied to determine the optimal gel sensitivity for optical computed tomography (CT). Photon beams (4 MV x-rays, 1×1, 2×2, 3×3 cm) irradiated a 10 cm diameter cylinder of gel. Using a cone beam optical CT scanner at λ = 590 nm, zero diffusion was observed by recording sequential 3D scans separated by 18 hours. Additional evidence was provided by sequential transmission photographs of a cuvette containing a sample that had been exposed to a 0.8 mm diameter, 1 mW, 594 nm, He-Ne laser beam and photobleached. Radiochromic bleaching is a fast process, complete within seconds of termination of irradiation. Dose sensitivity increases with cross- linking density and sulfuric acid concentration. The initial optical density limits dose sensitivity, requiring approximately 30 Gy for 10 cm diameter samples to have reasonable contrast. More sensitive but darker gels require smaller samples. A comparison of profiles through 3D reconstructed dose distribution showed identical profiles for a time interval of 18 hours. Visually the sample maintained this image for six months when stored at 4C in a dark refrigerator. Transmission photographs of the laser beam image recorded by photobleaching remained constant when stored a 23 C in the dark for ten months. Radiochromic genipin gelatin gels form a permanent and stable image when protected from bright visible light. This result is a new, non-toxic material for 3D dosimetry.

Diffraction detection of sucrose by electrophoresis in a microfluidic chip

Based on the change of diffraction pattern, a microfluidic chip electrophoresis detection system is developed. Using tris(hydroxymethyl)aminomethane (Tris) of 10 mmol/l as buffer and sucrose solutions (with concentration of 0.054, 0.1725, 0.24775 and 0.2975 g/ml respectively) as samples, quantity as tiny as 55 pl (pico-liter) of sucrose solution in the microfluidic chip (with a channel diameter of 60 μm) is detected successfully with an unfocused He-Ne laser beam (633 nm, 1 mW). The experiment is simple and the detection result is obvious.

Tomogram Visualization of Supersonic Jet Noise Using an Optical CT Method

Supersonic jet noise was visualized using a newly developed optical CT (Computed Tomography) method. From a converging round nozzle whose exit diameter is 8.0 mm, air is injected into the atmosphere. The pressure ratio is set at 2.25 (Mj=1.14), and an under-expanded jet is formed. A sound wave is pressure fluctuation, and the density fluctuates at the same time, Using a kind of schlieren method, the fluctuation of the density gradient is detected. A He-Ne laser beam passes through the supersonic jej, and the beam direction is slightly refracted due to the density gradient inside and around the supersonic jet. The beam refraction is converted to a brightness signal using a knife edge and a photo sensor. The signal obtained with the photo sensor is the integrated value along the laser beam path. Using a modified Abel inversion, the local refraction of the laser beam is calculated and the tomogram is re-constructed. It is shown that, using the optical CT method, non-intrusive acoustic measurement is possible even inside the supersonic jet. It is shown that the sound source of the screech tone exists around the 4th shock cell of the under-expanded jet, and that intensive fluctuation is observed not only in the shear layer but also along the center axis of the jet, implying the existence of the traveling shock wave.

Measurement of the intensity profile of a Gaussian laser beam near its focus using an optical fiber

We have designed a new pinhole-scan system to measure the Gaussian intensity distribution of a He-Ne laser beam that passes through a series of lenses. Our detection device uses a single-mode optical fiber as the so-called pinhole. One side of the optical fiber is fixed on the top of a motorized translation stage to capture the laser light, and the other side is connected to an optical power meter. A digital oscilloscope is used to observe the detected light intensity. When the translation stage as well as the fiber tip is moved across the laser beam, the oscilloscope displays the scanned trace of the laser beam intensity. The evolution of the intensity distribution of a focused laser beam is measured and then fitted to distributions predicted from Gaussian optics. The measured beam waist size is compared with the result of Gaussian-beam q-parameter analysis. Using this simple system we can easily observe the transverse intensity profile of a Gaussian laser beam in the (1+1)-dimensional plane in the vicinity of the focus.

Decoupling refractive index and geometric thickness from interferometric measurements of a quartz sample using a fourth-order polynomial

A Michelson interferometer setup was used to determine refractive index and thickness of a fused-quartz sample with no knowledge of either parameter. At small angles, < 10 degrees, the interferometer equation follows a fourth-order polynomial in the sample refractive index alone, effectively decoupling the sample thickness from the equation. The incident angle of the He-Ne laser beam versus fringe shift was fitted to the polynomial, and its coefficients obtained. These were used to determine refractive index to within 6 x 10(-4) of the known value with an accuracy of +/- 1.3%. Sample thickness was determined to an accuracy of +/-2.5%. Reproducibility of the rotating table was determined to be +/-2 x 10(-3) degrees.

Temperature Dependence of Single-Crystal Spinel (MgAl2O4) Elastic Constants from 293 to 423°K Measured by Light-Sound Scattering in the Raman-Nath Region

The temperature dependence of single-crystal elastic constants of synthetic stoichiometric MgAl_2O_4 spinel has been measured by the light-sound scattering technique in the Raman-Nath region. The crystal is set into forced vibration by a single crystal LiNbO_3 transducer coupled to one crystal face. A He-Ne Laser beam is diffracted by the stress-induced birefringence inside the crystal. The diffraction angle is determined from the distance between two spots exposed on a photographic plate by the first order diffracted beams as measured by a microdensitometer. The sound wavelength inside the crystal is then inferred from the laser diffraction angle. Combining the sound wavelength with the measured transducer frequency, the velocity inside the crystal is determined typically to a precision of 0·05 per cent. In this method, the measurement of velocity is not dependent on either the determination of sample length or on phase shifts at sample-transducer interface. Velocities of four pure modes, L//[001], T//[001], L//[110], and T//[110](P//[110] are measured in the temperature range between 293 and 423°K. A linear temperature dependence is fit to the data by a least square method.

Optical Properties and Sugar Content Determination of Commercial Carbonated Drinks using Surface Plasmon Resonance

In this study, an optical sensor based on Kretschmann SPR technique was used to detect the sugar content in commercial carbonated drinks. Three samples of carbonated drinks labeled as Coke, 100 Plus and F&N Orange have been chosen for angle scan SPR measurements. All the measurements were carried out at room temperature using He-Ne laser beam (632.8nm, 5mW) as a light source. The commercially available carbonated samples were diluted by adding distilled water to produce solutions with different sugar content. The results show that the shift of resonance angle (ΔθSPP) increases linearly with the sugar content in which the detection limit and sensor sensitivity could be quantified. Therefore, this technique could be used as optical sensor for detecting sugar content in carbonated soft drinks.

Electrically switchable optical vortex generated by a computer-generated hologram recorded in polymer-dispersed liquid crystals

A computer-generated hologram designed to generate an optical vortex was recorded in a cell filled with polymer-dispersed liquid crystal material under a collimated Ar+ laser beam operating at 514.5 nm. Owing to the photopolymerization-induced phase separation between the polymer and the liquid crystal, an index modulation was formed between the polymer-rich and liquid crystal-rich regions. A good optical vortex beam with high fidelity was reconstructed using a collimated He-Ne laser beam. The diffraction efficiency is estimated to be about 13%-17%. With a suitable voltage applied, the reconstructed optical vortex beam can be switched owing to the index change between the polymer and the liquid crystal.

High saturation solar light beam induced current scanning of solar cells

The response of the electrical parameters of photovoltaic cells under concentrated solar irradiance has been the subject of many studies performed in recent times. The high saturation conditions typically found in solar cells that are subjected to highly concentrated solar radiation may cause electrically active cell features to behave differently than under monochromatic laser illumination, normally used in light beam induced current (LBIC) investigations. A high concentration solar LBIC (S-LBIC) measurement system has been developed to perform localized cell characterization. The responses of silicon solar cells that were measured qualitatively include externally biased induced cell current at specific cell voltages, I(V), open circuit voltage, V(oc), and the average rate of change of the cell bias with the induced current, DeltaV/DeltaI(V), close to the zero bias region. These images show the relative scale of the parameters of a cell up to the penetration depth of the solar beam and can be obtained with relative ease, qualifying important electrical response features of the solar cell. The S-LBIC maps were also compared with maps that were similarly obtained using a high intensity He-Ne laser beam probe. This article reports on the techniques employed and initial results obtained.