Igor Peshko

Long-period gratings in optical fibres for chemical sensor applications

Analysis of long-period fibre grating (LPG) parameters and their mutual dependences are presented. LPGs were studied and optimized specifically for chemical sensor applications. It was found that absorption by the fibre cladding of some environmental gases, such as oxygen or water vapour, may result in a false signal generation. The principal limitation of the sensor sensitivity is connected to the longitudinal homogeneity of the fibre refractive indices.

Lens transformations of high power solid-state laser beams

Abstract Beam parameters of 300 W-class CW Nd:YAG lasers with double pump cavities have been investigated. The calculations have demonstrated that in the strongly pumped operating laser the amplitude of stresses in the rod can be decreased by a factor of approximately 1.5. A multibeam model of high power beam structure has been proposed. It has been shown theoretically and experimentally that 1.4–1.8 times reduction of the beam parameter product of a complex non-Gaussian beam may be achieved by placing a lens with a strength and location determined by laser parameters. An integrated parameters product has been proposed to describe the complex beams. In the range of possible pumping levels (3–10 kW) the output full divergence angle changed from 2 up to 23–28 mrad but in image space of the lens the variations of this value were no more than ±12%.

Robotic reconnaissance platform. I. Spectroscopic instruments with rangefinders

In this paper, basic principles of the design and implementation of a portable, multi-functional scientific instrument, operating from a robotic reconnaissance mobile platform are discussed. The current version of the instrument includes a multi-gas laser sensor, multi-functional spectrometer, isotopes identifier, cameras, and rangefinder. An additional set of sensors monitors temperature, pressure, humidity, and background radiation. All components are installed on a mini-robotic platform, which provides data acquisition, processing, and transmittance. The design focuses on the development of calibration-free, reliable, low power-consumption devices. To create a highly survivable, accurate, and reliable instrument, a concept of an inhomogeneous sensory network has been developed. Such a network combines non-identical sensors and provides cross-use of information received from different sensors to describe environmental conditions, to choose appropriate algorithms of data processing, and to achieve high accuracy gas-concentration measurements. The system uses the same lasers to operate different optical devices such as sensors, rangefinders, spectrometers, and isotopes identifiers. Among the innovative elements described in this paper, are a calibration-free, laser multi-gas sensor with range-finding option; a high signal/noise ratio transmittance spectrometer; a single-frequency laser with nano-selector; and low repetition-rate femtosecond fiber lasers operating in near- and middle- infrared spectral ranges. New detailed analyses of absorption spectroscopy theoretical approximations made it possible to achieve high-accuracy gas-concentration measurements with miniature optical sensors.

Fiber photo-catheters with spatially modulated diffusers for laser treatment of atrial fibrillation

A new generation of the optical fiber catheter has been developed for surgical treatment of atrial fibrillation with laser radiation. Atrial fibrillation (AF) is a heart rhythm abnormality that involves irregular and rapid heartbeats. The surgical maze procedure was the first treatment that offered a permanent solution for maintaining a normal sinus rhythm in patients with AF. This procedure involves the creation of a maze-like series of incisions in the left atrium, resulting in isolation of the pulmonary vein and removal of the left atrial appendage. To produce long continuous transmural lesions laser diodes operating in near IR range along with end-emitting fiber catheters have been used experimentally. The absence of side-emitting flexible catheters with the ability to produce long continuous lesions limits the further development of this technology. In this research, a new type of an optical catheter consisting of a flexible, spatially modulated fiber diffuser has been used to make continuous photocoagulation lesions for effective maze procedure treatments.

High power CW solid-state multilaser system

Abstract A laser system containing four CW Nd:YAG double-rod lasers, transforming optics and a fibre with input-output optics has been designed and investigated. It is shown that reduction of the beam parameter product of the non-Gaussian beams in the image space of the lens has made it possible to collect the emission of four lasers to the same fibre. Independent laser operation has provided the output power control in the range of 10–900 W with a stable light spot size on the input end of the fibre.

Time and Light

This book is devoted to Laser Pulses. In the modern laser world, the word “Pulse” covers pulse durations from microseconds (free-running laser) to tens of femtoseconds (1fs is 10-15 s) (mode-locked laser). It is possible to generate attosecond pulses (1as is 10-18 s) by using nonlinear processes. Recently, a new time range was discussed in publications: zeptosecond (1zs is 10-21 s). To generate pulses from milliseconds to femtoseconds, hundreds of different laser systems have been developed. They can typically generate pulses of specific durations, which are due to laser principles of operation, specific construction, parameters of gain medium, type of modulator, and so on.

Novel crystal gain medium for telecommunication devices

Routinely used erbium crystal lasers operate at the 3-μm spectral range. In the silica fibers the transparency window corresponds to the eye-safe range of 1.5-μm. The 4I13/2 -4I15/2 transition provides the lasing at this range in a glass matrix. However, in crystals it is of negligibly small intensity. To significantly intensify this transition, the (Gd,Y)3(Ga,Sc)5O12:Er3+ crystal has been chosen as the basis for the new laser crystal that is able to operate at 1.5-μm. The single crystal garnet films with thickness up to 18-μm were grown, using the method of liquid-phase epitaxy on the Gd3Ga5O12 substrates. The 20-mol% maximal concentration of Er3+ ions was achieved without luminescence quenching. The up-conversion processes were blocked by the addition of the Fe-ions sensitizer. As a result, at the same level of absorbed pumping power the luminescence intensity at the 1.5-μm band for the specially doped film was approximately two orders of magnitude higher than that compared with the crystal of the traditional content. The spectral width achieved with a new medium is a little smaller than 300 nm, which makes this crystal convenient for the femtosecond laser design. The laser tunable inside this range may provide hundreds of the optical channels for telecommunication or optical computer devices.

Fiber photo-catheters for invasive and less invasive treatment of atrial fibrillation

Atrial fibrillation (AF) is a heart rhythm abnormality that involves irregular, and often rapid, heartbeats. Recent studies demonstrate the feasibility of treating AF and other structural heart diseases with limited, left-atrial ablation lesion sets. These cardiac ablation procedures reduce the time required to perform the maze procedure surgery, and are less invasive. To produce long continuous transmural lesions, solid-state lasers and high power laser diodes, along with end emitting fiber optic catheters, have been used experimentally. These devices demonstrated promising results, but the absence of side emitting fiber flexible catheters to produce long continuous lesions limits the further development of this technology. In this research, a prototype energy delivery and control system located in a catheter, was demonstrated. The highlight of the proposed system is a flexible 10-cm fiber diffuser that can be used to make continuous photocoagulation lesions for effective maze procedure treatments. The system also includes: a flexible optical reflector; a distributed temperature sensor array for monitoring the temperature in the surrounding tissue; a series of openings for rapid self-attachment to the tissue (vacuum holder - gripper); and an optional closed-loop irrigating chamber with circulating coolant to cool the optical diffuser.

Multi-laser deposition technology for the nano-films of complex composition

A relatively cheap and compact deposition system, providing excellent high temperature superconducting films parameters, has been developed and studied. Y-Ba-Cu-O thin films were deposited routinely by the YAG double-laser system with the special optical beam and plasma plume shaping systems. Buffer CeO2 layers were deposited by the laser system as well. The properties of the plasma plume generated by the laser beam with a specific intensity distribution were investigated. A correlation between the superconducting film properties and the thermal schedule of the deposition process, the geometry of the set-up, the laser beam intensity distribution, the plasma plume shape and oxygen pressure has been found. Under optimal conditions Al2O3 - CeO2 - YBa2Cu3O7-δ - structures have provided the maximum critical current density of close to 107 A×cm-2 at 77 K in zero magnetic field. The films were used for the ultra high-frequency filters for the telecommunication devices.

Phase laser intracavity spectroscopy

A method of metallic thin-film surface conductivity monitoring is proposed and realized. The method is based on the dependency of the single-frequency laser output on the position of a thin absorbing film in the linear cavity. The real and imaginary parts of the surface conductivity of cobalt and chromium thin (~10 nm) films were measured for radiation with wavelength of about 1 µm.