mW Helium-neon Laser Research Articles

Dynamic interferometric measurements of thermally-induced deformations on telescope based on high-strain composite tape-springs

Thin carbon fibre reinforced polymer (CFRP) tape-springs are attractive structures for use in space-based optical instruments because of their compact stowed form, and their high dimensional stability when deployed. In this paper we present, with examples, two inexpensive methods to assess the thermal expansion properties of tape-spring structures: one based on strain gauges to obtain coupon level values, and another based on laser interferometry for structure level measurements. The strain gauge technique is a versatile approach that exploits the thermal output characteristics of the sensors. The thermal expansion characterisation of thin-composite samples measured a longitudinal expansion of 4.44 ppm/∘C and transverse expansion 5.95 of ppm/∘C. The interferometry system is designed with a view to capturing the displacements and tilts that occur when a structure with a low thermal mass, like a tape-spring, experiences a rapid change in flux, as occurs in the space environment. The homodyne interferometer is developed for three degree-of-freedom (DoF) measurements with a resolution of 10−8 m for distances and 10−6 rad for angles. The interferometric setup is based on the classical Michelson architecture and consists of few inexpensive commercial optical components. The source is a 0.8 mW Helium–Neon laser with a wavelength of 632.8 nm. The other elements include two spherical singlets, a right-angle prism, a cubic beamsplitter and a CMOS camera. The recorded interference fringes are analysed by using an algorithm based on Discrete Fourier Transform (DFT). Spectral information on the light intensity signals can be used to determine relative displacements and tilts. The dimensional stability of an optical payload based on high-strain composites was tested. The telescope has a deployable Cassegrain design, which uses six extendable members for the separation of its secondary mirror. Axial deformations between 20–30μm along with angle variations of the order of 0.1 mrad were recorded with good repeatability.

Mie scattering revisited: Study of bichromatic Mie scattering of electromagnetic waves by a distribution of spherical particles.

Two experiments to measure the size of microscopic dielectric spherical particles immersed in purified water with spheres of a nominal diameter 5.2 ± 0.15 μm have been carried out in order to revisit Mie scattering techniques. The first experiment uses a 1 mW helium-neon (He-Ne) laser with a wavelength of 632.8 nm, while the second one is carried out using a diode laser of 780.0 nm wavelength and a nominal power of 80 mW. The distribution of the scattered light intensity is recorded experimentally, and since the theoretical background has been known for several decades (see references), only a modest amount of theory is included. We considered the Mie scattering by a set of spheres of different diameters in our case with a distribution of sphere diameters with mean diameter 5.2 μm and standard deviation 0.15 μm. Our measured Mie scattering angular distribution accounts for the effect of the diameter distribution, which we assume to be a Gaussian distribution. Our results indicate that there is very good agreement between experiment and theoretical predictions. The technique we offer here is found to be useful to familiarize technicians who work in the areas of applied optics, such as chemistry, electronics, water contamination, and optical instruments with Mie scattering techniques, and who may not have a formal introduction to the electromagnetic theory. One specific area in which these techniques might be useful is the study of aerosols that may arise when naturally produced droplets from humans, such as those produced by coughing, sneezing, talking, and breathing, are present, as it happens in response to the Severe Acute Respiratory Syndrome Coronavirus 2, also known as SARS-CoV-2.

In Ukrainian

The results of the study on the strength and structural characteristics of matrices of various nature are presented, namely: cement paste, sand-cement mixture, hydroxyapatite (GAP), lamellar samples of fiberglass on an epoxy binder (resin of the brand LR 285, polymerization catalyst LH 286), fluoroplastic (PTFE), dependent on the content of the reinforcing component - multilayer carbon nanotubes (CNT), and PTFE, filled with aerosil (A300). For reinforcement of matrices, multilayer CNTs, synthesized by the method of catalytic CVD synthesis using three-component oxide iron-containing catalysts, were used. Mechanical tests of tensile and flexure composites were performed on a 2167 P 50 burst machine with a continuous automatic recording of the load-deformation diagram on a PC. The analysis of the sizes of CNT agglomerates was carried out using photon correlation spectroscopy (FCS). The particle size distribution function was determined on a ZetaSizer-3 (Malvern Instruments, UK) spectrometer with a correlator 7032 and a 25 MW (length wavelength λ = 633 nm) helium-neon laser LH-111. The dimensions of the coherent scattering regions were determined by the method of X-ray diffraction (DRON-3M, λ Со = 0.179 nm). The dependences of the strong characteristics of the systems filled with CNT: the cement paste, the sand-cement mixture, the layered samples of fiberglass on the epoxy binder, the hydroxyapatite (GAP), the PTFE, and the PTFE filled with A300 on the size of the structural regions formed by nanoscale filler. For liquid systems (cement paste, cement-sand mixture, epoxy resin), these are agglomerates of CNT, the sizes of which are nonlinearly dependent on the concentration of CNT. For solid: GAP - is porosity, PTFE - the size of the regions of coherent scattering of X-rays. It is shown that for low concentrations of nanosized fillers, the strength characteristics of composite materials are linearly increased from the resizing of the structural regions of nanosized fillers. The experimental dependences obtained are confirmed by theoretical calculations [40] on the determining role of nanosized regions of matrices, which are formed in interaction with nanosized filler, that is, the response of the matrix is proportional to the surface area of the interphase boundary.

Full-field coherence-gated holographic imaging through scattering media using a photorefractive polymer composite device

We report full-field, retroreflective holographic imaging through turbid media using a photorefractive polymer composite as a coherence gate. A four-wave mixing geometry was used to record and reconstruct two-dimensional images of test objects through 6.5 scattering mean-free-paths in real-time. Images with a transverse spatial resolution better than 42μm were acquired in a few seconds using a 6.3mW helium neon laser at 633nm. The photorefractive devices used are based on a poly (N-vinylcarbazole) (PVK):2,4,7-trinitro-9-fluorenone dimalenitrile (TNFDM) charge transport network, doped with the electro-optic chromophore 1-(2′-ethylhexyloxy)-2,5-dimethyl-4-(4″-nitrophenylazo)benzene (EHDNPB).

The non-contact monitoring of heart and respiratory rates using laser irradiation: an experimental simultaneous monitoring with and without clothes during biochemical hazards

The purpose of this study is to develop a non-contact method to evaluate the heart and respiratory rates simultaneously using a single optical sensor which can be used without the removal of clothes before a decontamination procedure in biochemical hazards. We measured the heart and respiratory rates with and without clothes to assess the vital sign monitoring before decontamination. In order to monitor the heart and respiratory rates of rabbits simultaneously, the respiratory and cardiac peaks were separated using fast Fourier transform from a 5 mW helium-neon laser (wavelength 632.8 nm) reflected off the chest walls of rabbits. A cloth (50 mm 2 50 mm, 2 mm thick) was placed on the chest of the rabbits to simulate the vital sign monitoring with clothes. The heart rate measured using this method agreed with the rate derived from an electrocardiogram ( r = 0.82, p <0.05). The respiratory rate correlated with the manually measured respirator rate ( r = 0.93, p <0.05). This method appears promising as a non-contact method for monitoring the heart and respiratory rates of patients under biochemically hazardous conditions.

Photosensitive chemical and laser light treatments decrease epizootic hemorrhagic disease virus associated with in vitro produced bovine embryos

Photoinactivation was employed to eliminate EHDV-2 from in vitro produced bovine embryos experimentally exposed to this virus. Immature oocytes were matured, fertilized, and cultured in chemically defined conditions. All treatments were performed on zygotes. Developmental potential of zygotes and cell numbers of resulting hatched blastocysts were assessed after exposure to a 1 mW helium neon laser (633 nm, red) for 1, 5, 10, and 15 min; the photosensitive chemicals hematoporphyrin (15 μ;M) and hypericin (1 and 10 μ;M) for 15 min; a combination of 10 μ;M hypericin and laser light for 1, 3, or 5 min; and a combination of 15 μ;M hematoporphyrin and laser light for 1, 2, or 3 min. There were no significant differences among proportions of embryos developing or cell numbers after treatment with or without exposure to laser light alone for up to 10 min. No differences were observed after exposure of zygotes to photosensitive chemicals alone. Exposure to 10 μ;M hypericin and 5 min of laser light or 15 μ;M hematoporphyrin and 2 min of laser light compromised zygote developmental potential. After exposure to 10 6 TCID 50/mL EHDV-2 for 90 min groups of 10 zygotes were exposed to 10 μ;M hypericin or 15 μ;M hematoporphyrin and laser light to inactivate the virus. Hematoporphyrin was effective with 3 min light exposure at reducing the percentage of EHDV-2 contaminated zygote pools (16.7%) as compared to EHDV-2 exposed pools without treatment (88.9%) but hematoporphyrin + 1 min light was ineffective. Hypericin + 3 min light provided an intermediate effect (55.6%).

Low intensity laser irradiation in the treatment of recalcitrant radiation ulcers in patients with breast cancer--long-term results of 3 cases.

Radiotherapy can be followed by recalcitrant skin ulcers. As low intensity laser irradiation has been demonstrated to have a beneficial effect on impaired wound healing, we investigated its efficacy and safety in three patients with chronic radiation ulcers. The three patients, previously mastectomized due to breast cancer, with recalcitrant radiation ulcers of the skin were treated with a 30 mW helium-neon laser (wavelength: 632.8 nm, intensity: 3 mW/cm2, dose: 30 J/ cm2) three times weekly. In all patients, complete wound closure was achieved within a period of 7, 5, and 8 weeks. One patient died 6 weeks after laser treatment due to tumor cachexia. Neither of the other patients showed recurrence of radiation ulcers or neoplasm during a follow-up of 36 months. Low intensity helium-neon laser irradiation has been shown to be effective in the induction of wound healing in radiotherapy-induced ulcers in three patients with breast cancer.

Investigation of vibrational and photoluminescence spectra of nanocrystalline silicon by micro-Raman spectroscopy using various laser powers

The Raman spectra of silicon nanocrystals embedded in silicon oxide and in porous silicon were measured at various laser powers. It was found that the Si–Si stretching Raman peak shifts to lower wavenumbers and broadens when the laser power increases. The effect is significant and reversible, i.e. the peak returns to its former position when the laser power is decreased to the initial level. It was found that this reversible phenomenon is caused by an increase in bond length due to the heating effect of the laser. In addition, the appearance of weak bands on both sides of the main Si–Si stretching mode peak at 155, 332, 620, 940, 2087, 2114 and 2145 cm−1 was observed at high laser power. It was found that the first four bands could be attributed to one- and multi-phonon Raman scattering and the last three bands are the expected SiH2, SiH and SiH3 stretching vibration modes. The photoluminescent spectrum was measured with the use of 1.959 eV illumination from an 11 mW helium–neon laser. It was found that the photoluminescence spectrum consists of a broad line centered at 1.79 eV with a full width at half-maximum of 0.21 eV and a tail located in an energy region higher than the laser incident excitation energy. Based on the analysis of Raman scattering spectra and the assumption that the luminescence spectrum arises from the ensemble of various sized particles distributed in the material, it is suggested that the later band of photoluminescence should be excited by the Raman scattering light in silicon nanocrystals. Copyright © 1999 John Wiley & Sons, Ltd.

Induction of complete wound healing in recalcitrant ulcers by low-intensity laser irradiation depends on ulcer cause and size.

Chronic skin ulcers still represent a therapeutic challenge in dermatology. Among the various non-invasive treatment modalities used for the improvement of impaired wound healing, low-intensity laser irradiations are gaining an increasing body of interest. We used low-intensity laser irradiations delivered by a 30 mW helium-neon laser at an energy density of 30 J/cm2 three times weekly for the induction of wound healing in ulcers of diverse causes. Twenty patients with the same number of ulcers, which had previously been treated by conventional wound care for a median period of 34 weeks (range: 3-120 weeks) without any significant evidence of healing, were included in the study. Concerning the underlying disorders, patients were divided into four groups: diabetes, arterial insufficiency, radio damage and autoimmune vasculitis. In all ulcers, complete epithelization could be induced by laser therapy. No amputation or any other surgical intervention was necessary and no adverse effects of any kind were noted during low-intensity laser treatment. Regarding the different diagnoses, a statistically significant difference was noted (P = 0.008): ulcers due to radio damage healed significantly faster than those caused by diabetes (6 weeks [range: 3-10 weeks] vs. 16 weeks [range: 9-45 weeks], P = 0.005). Wound healing in autoimmune vasculitis (24 weeks [range: 20-35 weeks]) required longer than in radiodermitis, although the difference was not significant. In addition to the diagnosis, wound size was found to be an important factor influencing the duration of wound closure (P = 0.028), whereas duration of previous conventional treatment (P = 0.24) and depth (P = 0.14) showed no effect. Our results indicate that low-intensity laser irradiation could be a valuable non-invasive tool for the induction of wound healing in recalcitrant ulcers, and that healing time is correlated with the ulcer cause and size.

Indirect thermo-optical detection for capillary electrophoresis

Indirect thermo-optical detection for capillary electrophoresis is described first. A 20 mW helium-neon laser (632.8 nm) was used to provide the pumping beam and a 2 mW helium-neon laser (632.8 nm) supplied as the probe beam; Methylene Blue dye was used as a background absorber. The addition of ethanol to the background electrolyte solution can be performed to reduce adsorption of Methylene Blue onto the capillary wall. The detection method was applied to the detection of amino acids separated by capillary electrophoresis. The detection limit for lysine was 5 × 10 −6 mol l −1 (signal-to-noise ratio, 2).

Dose and temporal parameters in delaying injured optic nerve degeneration by low‐energy laser irradiation

Low-energy laser irradiation has been reported to postpone the degenerative processes in crushed optic nerves of rats, which are part of the nonregenerable mammalian central nervous system. In the present study, we evaluated the optimal irradiation parameters for this purpose. Optic nerves of 141 rats were subjected to crush injury and then irradiated through the eye, starting at different points of time before or after the injury, for different durations and periods, using various intensities of either helium-neon laser or noncoherent infrared light (904 nm). The effect was evaluated by measurements of the compound action potentials of the nerve segments between the site of injury and the optic chiasm. The compound action potential amplitude of the crushed nonirradiated nerves, as measured 2 weeks after the injury, was found to be 0.51 +/- 0.30 mV, in contrast to 3.10 +/- 1.03 mV measured in 232 normal nerves. Irradiation with a 10.5 mW helium-neon laser for 2 and 3 min once a day for 14 consecutive days resulted in maximal preservation of action potentials (1.78 +/- 0.72 and 1.95 +/- 0.71 mV, respectively). Irradiations beginning immediately prior to the injury were as effective as irradiations beginning soon after it. Irradiations for longer than 3 min or twice a day aggravated the damage. Noncoherent infrared light was ineffective or adversely affected the injured nerves. Our experiments suggest that optimal delay of posttraumatic optic nerve degeneration in rats is attainable with 10.5 mW helium-neon laser irradiations for 2 or 3 min once a day for 14 consecutive days.

Characterization of thermal modulation of electrical conductivity: a small volume absorbance measurement technique

Laser-induced thermal modulation of electrical conductivity is a new photothermal method for the measurement of minute absorbance in sub-nanoliter liquid samples. In this paper, a model is presented for the technique. This model is based upon the interaction of a Gaussian laser beam with a cylindrical, homogeneous electrolytic resistor. Particularly simple results are produced if the laser beam spot size is much smaller than the diameter of the electrodes. The theory is verified with respect to the electrode spacing and to the laser power, spot size, and chopping frequency; the highest sensitivity occurs with low chopping frequency, high laser power, and small electrode spacing. The signal is independent of laser spot size, as long as the beam does not illuminate the electrode surface. The precision of the measurement is dominated by shot noise in the current flow through the electrolytic resistor. One point absorbance detection limits of 5.5 × 10−6 measured across the 76-μm diameter electrode wires are obtained in aqueous solution with a 5- mW helium–neon laser. With this instrument, the difference in the absorbance of water and deuterated water is easily determined at 632.8 nm. Keywords: thermal modulation of electrical conductivity.

Remote sounding of aerosols in the lower atmosphere using a bistatic CW helium-neon lidar

A bistatic, CW (continuous wave) lidar (light detection and ranging) system has been developed at the Indian Institute of Tropical Meteorology, Pune, India for remote sounding of atmospheric aerosols. The system comprises a Spectra-Physics Model 159, 5 mW helium-neon laser as transmitter and a 25 cm Newtonian telescope-photomultiplier assembly as receiver. The details of the experimental set-up and results of preliminary observations of aerosols carried out in the lowest layers (up to 300 m AGL) of the atmosphere are presented. The results were found to be in agreement with those of the model predicted aerosol number density profile obtained by other investigators in the height region of observations. The variations in the height distribution of aerosols are explained in the light of the atmospheric conditions prevailing over the measuring site.

The coupled-cavity laser interferometer with rationally related cavity lengths

Single-ended commercial gas lasers are used to measure small changes in the optical length of an external cavity. The ratio of the length of the laser cavity to the length of the external cavity is chosen to be a rational fraction and this permits a wide range of external cavity lengths to be used in practice. The denominator of this ratio is set equal to the number of longitudinal lasing modes s, and this enables each mode to contribute sequentially to the measurement, producing one cycle of modulation in lasing intensity for each lambda /2s change in length. A short 7.5 mW helium-neon laser was used to record successive lambda /8 changes in length of external cavities that had a gross length ranging from one quarter to nineteen quarters of the laser cavity length. In principle greater sensitivities can be obtained by using longer gas lasers.

Observation of optical bistability in smectic a liquid crystals

The first observation of optical bistability in smectic A liquid crystals is reported. This was achieved with a 5 mW helium-neon laser in a dielectric mirror/metal mirror Fabry-Perot cavity. The switching power was found to be 360 to 420 mW (in a 30 μm diameter spot) depending on the relative orientation of the plane of polarisation and the long molecular axes.

Immuno-gold labeling for flow cytometric analysis

Colloidal gold particles coated with goat anti-mouse immunoglobulin antibodies were used to analyse surface antigens on various cell types by flow cytometry. The gold-labeled cells showed an increasing signal amplification in the 90° light scatter with increasing wavelength of the incident laser light, reaching a more than 10-fold amplification at 632.8 nm. This wavelength was provided by a 0.5 mW helium-neon laser. The magnitude of the signal amplification due to the gold label as well as the specificity of the label was sufficient for quantitative discrimination between positive and negative cells. Cell viability was not affected by the gold label. Mouse spleen cells were labeled with various combinations of FITC- and gold-conjugated antibodies. It was found that the gold and fluorescent labels did not interfere with each other. Colloidal gold may thus be used as an additional label for multiparameter cell analysis and sorting. Biparametric cell analysis/sorting of surface antigen-labeled cells (label versus low-angle scatter) becomes possible even with a low energy helium-neon laser.

Aperture plates for Fraunhofer diffraction

An undergraduate experiment on Fraunhofer diffraction is described. The apertures are made by electron beam lithography in a chromium film on an optical flat, giving a marked improvement of performance over glass photographic plates. Computer control of the electron beam allows complex repetitive apertures to be constructed giving clear demonstrations of the principles of Fraunhofer diffraction. The light source is a 1 mW helium-neon laser. Patterns from simple apertures may be measured to obtain a quantitative test of the theory and more complex apertures illustrate theory such as the use of superposition and the convolution theorem.

Mixed-valent iron in synthetic rasvumite, KFe2S3

cases apparently typical structures developed at the interface, d) To test the possibility of mass-transfer within the solution, a 0.5 mW helium-neon laser illuminated a small area just below the surface, and the solution mixed with different types of dusts, e.g. aluminum dust and fumed silica (Aerosil). Similarly, hydrophobic reverse-phased fumed silica (Aerosil R972) was sprinkled on the surface. Laser illumination very clearly showed individual red speckles of the dust particles [14], however no bulk or surface movements were apparent during UV illumination. e) Kafri recently developed a sensitive deflectometry-type method [15] which utilizes laser light and Ronchi rulings. Hydrodynamic movements are easily detected by this technique, yet again no such movements were seen in our case. It seems to us that the phenomenon is purely due to diffusion processes or, at the most, to microscopic movements which we have not yet been able to detect. In our forthcoming paper we have expanded the phenomenon to purely thermal systems, suggesting that symmetry breaking is due to the buildup of concentration instabilities at the interface, as postulated theoretically by several authors [16].

Laser activation of phytochrome-controlled germination in Pinusbanksiana

A 100 ms exposure from a 5 mW helium–neon laser was sufficient to potentiate fully phytochrome-controlled germination in Pinusbanksiana Lamb. The energy requirement for the brief, high-intensity light exposure was comparable to that for a much longer, low-intensity light exposure. As a result, the laser may be valuable in studies of the germination process and the primary mode of action of phytochrome.

An arrangement for observing Fresnel diffraction

Fresnel diffraction assumes a spherical wavefront which occurs when the source-obstacle distance is small. With a conventional source there is some difficulty in projecting a sufficiently intense image of the diffraction pattern for demonstration to a large class. In this experiment the beam from a 2 mW helium-neon laser was deliberately made divergent using a double concave lens placed over the exit aperture. A projector lens, placed after the diffracting system, enabled the image to be projected on a screen 80 cm beyond. The magnification could be changed easily by moving the obstacle towards or away from the laser and in this experiment ranged from *20 to *100.