Vladimir Svirid

Novel optical fiber refractometric transducer employing hemispherical detection element

We present the results of a theoretical numerical analysis of a novel fiber optic refractometric transducer. It consists of a hemispherical glass detection element and a pair of the multimode optical fibers attached symmetrically to the elements flat equatorial plane. The internal reflection of light from the elements spherical surface is sensitive to the refractive index of the surrounding medium. We exploit several internal reflections in series and the focusing of the beam by the elements spherical surface to achieve enhanced sensitivity to the refractive index of the surrounding medium and reduced intrinsic optical loss in the transducer. We present the data on the effect of transducers parameters on its transmission function. We show that the transducer can operate in a relatively wide range of the refractive index of the surrounding medium (we show this for the interval n = 1.0 to n = 1.45). We also present experimental data confirming our theoretical results.

Linear and steplike characteristics in an optical fiber refractometric transducer with hemispherical detection element

We present the results of a theoretical numerical analysis of transmission characteristics of a fiber optic refractometric transducer with a hemispherical glass detection element. In this transducer, the internal reflection of light from the elements spherical surface depends on the refractive index of the surrounding medium. We examine the effects of the transducers geometrical and optical parameters and its refractive index on the transmission function, its nonlinearity, and the transducers sensitivity to the refractive index of the surrounding medium. We show that through a proper choice of the transducers material and geometrical parameters, it is possible to obtain a transmission function of any necessary span over a wide interval of the refractive index of the surrounding medium (from n = 1.0 to 1.7), and to modify the form of the transmission function from a linear one to a steplike one in virtually the same device. This permits us to use the proposed transducer for two contrasting applications: assessing the refractive index, and discriminating between two liquids or between air and a liquid, as in the detection of liquids, level measurement, etc. In addition, it is possible to adjust the transducer input range to the refractive index of a particular fluid (or fluids) of interest.

Laser Doppler velocimeter miniature differential probe for biomedical applications

The dynamic sensors for speed and flow are applied in pathological physiological research of the cardiovascular system and for the study of blood flow in the capillaries. The use of laser Doppler anemometry (LDA) method is considered the major prospective for this application. This method is based on the Doppler shift of the frequency of laser radiation scattered by blood particles in movement. However, to have access to inner organs, a small-size delivery system and optical probe are necessary. In this paper, we report a novel miniature optical probe for the differential-type LDA, suitable for use in small blood vessels and in other small channels. For the construction of the probe, two-core single mode optical fiber was used. This fiber had two anisotropic 8 (mu) cores, located symmetrically with respect to the fiber axis. The separation between them was 25 (mu) . In the fiber, a directional coupler was integrated near the fibers remote end. The coupler was fabricated by heating of a small section of the fiber, with simultaneous elongation of this section. For heating, the carbon-dioxide laser was utilized. The carbon-dioxide laser was also used to fabricate a lens at the fiber tip. At the fiber entrance, the laser light was launched in one of the fibers cores. The fiber was typically of several meters long. Near the fiber end, this radiation was splitted by the directional coupler, and the second core was excited too. At the fiber tip, the fused lens provided collimation of the emerging beams and secured their intersection in front of the fiber tip. In this intersection volume, the interference field was formed. In the flow, this periodic pattern resulted in Doppler frequency shift of the light scattered by moving particles. This probe was successfully used together with the LDA signal processing equipment for velocity measurement in small tubes for blood-flow simulation experiments. In the probe, the two cores are identical, and the between the directional coupler and the fiber tip is very small. Thereafter, all extrinsic fields and effects have identical influence on the propagation constant of each core. Hence, the resultant parasitic phase modulation, that is the main problem in the fiber-based differential LDA, is negligible in this probe. This is the principal advantage of this probe. However, its small size and integrated nature are also of value for biomedical applications.

Fiber optic multipoint high-resolution level sensor for biomedical applications

Fiber-optic sensors are attractive for biomedical applications primarily because of their non- electrical and non-conductive nature. This secures the safety of use and immunity to electromagnetic interference. In addition to these advantages, the optical-fiber level-sensor presented here has a small size, high accuracy, and fast time response. The sensor probe is chemically passive and can be easily sterilized. These features make the sensor attractive for numerous applications in physiology, biochemistry and medicine. The level-sensor presented here is a multipoint discrete optical-fiber device employing an array of small-size liquid- sensitive optical refractometric transducers of new type. The array of such transducers is connected via multi-fiber optical cable to the optoelectronic transmitter-receiver unit of the sensor. It performs an intelligent quasi-continuous level monitoring of a fluid. The sensor accuracy, resolution and level measurement range depend on the array length and the total number of the transducers employed. In case of the most close spacing of the transducers, the sensor level-resolution is better than plus or minus 0.2 mm.

Optoelectronic multipoint liquid level sensor for light petrochemical products

In this article we describe an optoelectronic sensor for assessing the level of light petrochemical products in technological tanks at the oil refineries. This sensor employs the multi-element vertical array of discrete micro- optical refractometric transducers. The transducers are made of silica glass and have the conical shape. In the air, each transducer operates as a tiny retro-reflector that optically couple together two multimode optical fibers. The optical coupling in the transducer is due to the internal reflection at the conical surface. The amount of the coupling depends on the refractive index of the surrounding media. In a fluid, the total internal reflection vanishes and the coupling becomes negligibly small. The number of immersed transducers is a measure of the fluid level in the reservoir. Because of the significance of the transducer transmission function, it is evaluated in detail under various combinations of the geometrical parameters of the micro-optical structure and connecting optical fibers. The numerical ray tracing shows that the form of the transmission function can be modified by change of some geometrical parameters of the structure.

Laser technique for anatomical-functional study of the medial prefrontal cortex of the brain

The brain represents one of the most complex systems that we know yet. In its study, non-destructive methods -- in particular, behavioral studies play an important role. By alteration of brain functioning (e.g. by pharmacological means) and observation of consequent behavior changes an important information on brain organization and functioning is obtained. For inducing local alterations, permanent brain lesions are employed. However, for correct results this technique has to be quasi-non-destructive, i.e. not to affect the normal brain function. Hence, the lesions should be very small, accurate and applied precisely over the structure (e.g. the brain nucleus) of interest. These specifications are difficult to meet with the existing techniques for brain lesions -- specifically, neurotoxical, mechanical and electrical means because they result in too extensive damage. In this paper, we present new laser technique for quasi-non- destructive anatomical-functional mapping in vivo of the medial prefrontal cortex (MPFC) of the rat. The technique is based on producing of small-size, well-controlled laser- induced lesions over some areas of the MPFC. The anesthetized animals are subjected to stereotactic surgery and certain points of the MPFC are exposed the confined radiation of the 10 W cw CO2 laser. Subsequent behavioral changes observed in neonatal and adult animals as well as histological data prove effectiveness of this technology for anatomical- functional studies of the brain by areas, and as a treatment method for some pathologies.

Laser blood irradiation effect on electrophysiological characteristics of acute coronary syndrome patients

This paper treats electro-physiological effects of the low- level laser irradiation of blood (LBI). The data presented here are based on the observation of almost 200 patients suffering from the acute disruption of coronary blood circulation, unstable angina pectoris and myocardial infarction. Statistically significant changes of the electro-physiological characteristics were observed in the group of 65 patients, treated by the LBI. In particular, the significant 6 percent extension of the effective refractory period was observed. The electrical situation threshold has increased by 20.6 percent. The significant changes of some other important electro-physiological characteristics were within the range of 5-15 percent. In this paper, the data obtained on the LBI effectiveness are compared also with the results obtained on 94 patients who in addition to the standard anti-angina therapy were treated by the autohaemo- transfusion performed simultaneously with the UV-light irradiation of the transfused blood. The results obtained demonstrate the significant positive effect of the low energy LBI. The electrophysiological data obtained have good correlation with observed anti-arrhythmic effect of the LBI. This is proved by the data obtained on the electro- physiological characteristics of the cardiovascular system and by other clinical data on the experimental and control group of patients. In the course of this research the exact effect of the low level LBI was established. LBI led to the pronounced positive changes in electro-physiological characteristics of the cardiovascular system of the patients, it also led to the pronounced anti-arrhythmic effect.

Optical-fiber discrete liquid-level sensor for liquid nitrogen

We present a prototype optical-fiber liquid-level sensor for measuring the static and dynamic level of liquid nitrogen in large cryogenic hydraulic systems. This version of sensor is intended for use for various tests of the cryogenic hydraulic systems at their design stage. The sensor employs a total of 140 highly sensitive optical-fiber point detectors of liquid in a form of vertical linear array. The liquid level measurement range is of 1.6 m, a vertical resolution is up to 5 mm. The optical detectors of liquid are multiplexed by means of matrix-type optical fiber network, which operates under robust level-tracking algorithm. A sensor of this type can be used for measuring the level of other cryogenic fluids.

Laser-induced accurate frontal cortex damage: a new tool for brain study

New laser-based technique for anatomical-functional study of the medial prefrontal cortex (MPFC) of the brain of experimental animals (rats) is presented. The technique is based on making accurate well-controlled lesions to small MPFC and subsequent observing behavioral alterations in the lesioned animals relative to control ones. Laser produces smaller and more accurate lesions in comparison to those obtained by traditional methods, such as: mechanical action, chemical means, and electrical currents. For producing the brain lesions, a 10 W CO2 CW laser is employed for reasons of its sufficiently high power, which is combined with relatively low cost-per-Watt ratio. In our experience, such power rating is sufficient for making MPFC lesions. The laser radiation is applied in a form of pulse series via hollow circular metallic waveguide made of stainless steel. The waveguide is of inner diameter 1.3 mm and 95 mm long. The anesthetized animals are placed in stereotaxic instrument. Via perforations made in the skull bone, the MPFC is exposed to the laser radiation. Several weeks later (after animal recuperation), standard behavioral tests are performed. They reveal behavioral changes, which point to a damage of some small regions of the MPFC. These results correlate with the histological data, which reveal the existence of small and accurate MPFC lesions. The present technique has good prospects for use in anatomical- functional studies of brain by areas. In addition, this technique appears to have considerable promise as a treatment method for some pathologies, e.g. the Parkinsons disease.

Holographic-field laser Doppler velocimeter with increased velocity measurement range for biomedical applications

In many applications of Laser Doppler Velocimetry object velocity varies with time within some more or less wide range. Large variations present a problem for signal processing. This difficulty may be reduced in the proposed new Laser Doppler Velocimeter which utilize the periodic polyharmonic spatial probe field. The probe field is formed by the holographic technique employing the periodic wavefront modulator and the field-forming hologram. By proper selection of the parameters of these components, the probe field with pronounced high-order spatial harmonic content is obtained. This results in the presence of several Doppler frequency harmonics in the output signal, for the single value of object velocity. One of these harmonics is used for velocity determination. The choice of a particular harmonic depends on how well it fits into the frequency range of the instruments electronics. If the object velocity becomes too small or too large, some other Doppler frequency harmonic which now fits better into the instrument frequency range is used for further processing and velocity determination. Experimentally, the multi-harmonic probe field was obtained and the effect of its spatial structure on Doppler signal composition was studied.