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The evolution of the Er3+:YAG thermal radiation spectra at heating up to the melting point was investigated in the visible range when growing a crystal fiber by the Laser-Heated Pedestal Growth (LHPG) method. The Er3+:YAG melt of about 1 mm thickness radiates like a black body in several spectral bands sometimes different from the crystal absorption lines. The real melt temperature in the middle of the growth zone was estimated as 2620 ± 15 K. The spectral profile of Er3+:YAG emissivity in the visible range for a melt layer of about L ≈ 1 mm at 2620 K is shown in the Figure.

The refractive index (RI) of a sapphire crystal melt was determined at high temperatures (exceeding 2350 K) in the visible spectral range. Data were obtained from the analysis results of the state of polarization of the intrinsic thermal radiation of the melt during the laser-heated pedestal growth process. The derived sapphire melt RI is n = 1.72 ± 0.02 for λ = 550 nm, and the linear part of the dispersion in the range 400–750 nm is characterized by the coefficient dn/dλ = −(1.93 ± 0.01) × 10–4 nm − 1.

Temperature distribution along a single crystal fiber molten zone in the laser heated pedestal growth (LHPG) process of pure sapphire (Al 2 O 3 ) and yttrium–aluminum garnet (Y 3 Al 5 O 12 ) fiber was measured for the first time. The temperature was determined from thermal radiation spectra measurements in the visible spectral range. Our measurements indicate the existence of local temperature minimum in the region of source rod melting.

A new method for measuring the refractive index of crystals and melts at high temperatures is presented. The refractive index of an Er3+:YAG crystal melt is determined during the laser-heated pedestal growth process close to the melting point. The main idea is to use the maximal difference in the intensities of two polarizations of thermal radiation passing the melt-air interface. From the Fresnel equations, it follows that this difference is almost proportional to the refractive index. Angular diagrams of the thermal radiation of the melt for two polarizations are analyzed. The obtained value of the refractive index of the Er3+:YAG melt is n = 1.84 ± 0.01 in the wavelength range of 550–620 nm.A new method for measuring the refractive index of crystals and melts at high temperatures is presented. The refractive index of an Er3+:YAG crystal melt is determined during the laser-heated pedestal growth process close to the melting point. The main idea is to use the maximal difference in the intensities of two polarizations of thermal radiation passing the melt-air interface. From the Fresnel equations, it follows that this difference is almost proportional to the refractive index. Angular diagrams of the thermal radiation of the melt for two polarizations are analyzed. The obtained value of the refractive index of the Er3+:YAG melt is n = 1.84 ± 0.01 in the wavelength range of 550–620 nm.

A setup is developed for measuring optical characteristics of opaque and translucent solids in the temperature range of 25 to 1600°C and spectral range of 0.65 to 10.6 µm. Procedures of calibration experiments and measurements of spectral and integral emissivity are described. These procedures allow spectral and integral emissivity and spectral and integral reflectances of various materials, including translucent ones, to be measured accurate to about 10% in the spectral range of 0.65 to 10,6 µm and temperature range of 25 to 1600°C. Optical characteristics of materials are measured at the atmospheric pressure in the normal oxygen atmosphere or in the atmosphere with reduced oxygen content (inert gas or carbon dioxide blowing on the frontal surface of the samples). The accuracy of the thus obtained data on temperature and spectrum dependences of optical characteristics of materials allow measurements to be performed for developing various structures capable of operating at high temperatures.

We demonstrate the employment of single-crystal optical fibres based on lithium niobate for doubling the laser radiation frequency. The measured characteristics of the fibre confirm its high quality and spatial homogeneity. Parameters of the frequency doublers for neodymium laser radiation (λ = 1 mm) based on fibre and bulk single crystals are compared. Single crystals are grown by the method of laser-heated pedestal growing with heating by radiation of a CO{sub 2} laser (LHPG-method). (nonlinear optical phenomena)

Single-crystal Ln2O3 (Ln = Sm, Eu, Gd) fibers are grown by the laser-heated miniature pedestal technique. The relationship between the microstructure of fibers and their plasticity is analyzed using scanning electron microscopy, energy-dispersive microanalysis, electron backscatter diffraction, and X-ray methods. It is shown that the distinction between ductile and brittle fibers is determined basically by the difference in their microstructure. The fracture of samarium oxide fibers is associated with the formation of oxycarbonate phases on their surface. The most promising are the fibers of gadolinium oxide, having the most perfect microstructure, moisture and a carbon dioxide resistance, and a wide range of transparency.

The efficient technology is developed for growing high-quality doped single-crystal fibres by the mini-pedestal method with laser heating. The technology can be used to fabricate high-quality doped single-crystal fibres with a controllable radial gradient of the refractive index. The refractive-index profile in single-crystal fibres is studied experimentally. The efficient operation of a Nd3+ : YAG single-crystal fibre laser in the waveguide regime was demonstrated upon longitudinal pumping by a laser diode.

Two principles of producing quartz light guides with an elliptical section using the radiation of CO2 laser are described. The possibility of deformation of quartz preforms in the course of drawing quartz light guides is demonstrated. The process of manufacture of two types of elliptical quartz light guides is analyzed.

A thorough spectroscopic examination of the co-doped Yb:Ho:YSGG system was performed with the goal of achieving cw laser action on the 3 μm Ho 5I6→5I7 transition. Yb has very good pump absorption properties, and a highly efficient process transfers the excitation to the Ho upper laser level, which has a lifetime of ~400 μsec. The lower laser level lifetime can be reduced from 9msec to 1.5 msec by the addition of 2% Eu as a deactivator without adversely affecting the upper laser level population. An undesirable upconversion process was discovered, though its effect can be minimised using high Yb and Ho concentrations, as these make the energy transfer rate so fast that it dominates the upconversion rate. The ideal composition derived from our studies is 50% Yb:8% Ho:2% Eu, and laser operation at duty cycles in excess of 0.25 appears possible.

Single crystal fibres on a basis rare-earth oxides are promising materials for technical application, in particular for radiation delivery in a near and mid-IR range. In the fibres shape Eu3+:Y 2 O 3 [1], Ln3+:Gd 2 O 3 (Ln=Nd, Eu, Er) [2,3] single crystals have been received earlier and their luminescent properties have been studied. The goal of our study consisted in the interrelation analysis between a microstructure of fibres and their such property as the plasticity expressed in their ability to be easily bent. Another goal was the study of nonlinear properties consisted in the possibility to produce super continuum generation during the transmission of the ultrashort light pulses. Fibres Ln 2 O 3 (Ln=Sm, Eu, Gd) have been grown up by a method of “a laser minipedestal” on ZrO 2 crystal seed. Among the grown up fibres there were both fragile, and flexible plastic. According to X-ray crystal phase analysis in all of them Ln 2 O 3 are crystallized in monoclinic system and do not contain additional cubic crystal phase stable at low temperatures (a limit of detection of about 1 %). A series X-ray diffraction patterns obtained with initial, bent and straightened fibres shows, that at deformation the reflexes on Laue pattern are diffused, but there is practically full restoration of clearness of reflexes at restoration of the initial shape of a fibre. The morphology of the samples surface was studied, the chemical composition is determined by the X-ray microanalysis, orientation of crystals is established by a method of diffraction of back scattered electrons (EBSD). On the fibres surface the rings are observed and they are allocated with distances between them of about 0,3–2 µm (Fig. 1)

The operating principle and characteristics of applicators based on disperse magnetic systems intended for deposition of protective polymer coatings on quartz light guides are described. The possibility of controlling the parameters of coatings in drawing light guides is demonstrated.

The paper shows the advantages of graded furnaces for the thermal polymerization of a silica-organic polymer cladding for silica fibers. Owing to the optimal longitudinal distribution of the heaters a fivefold increase of the fiber drawing speed can be achieved using heaters of the same lengths and power.

The problem of controlling the diameter of a fabricated fiber with the help of an auxiliary low-power laser heater is analyzed.

The results of numerical modeling of the process of drawing a quartz blank into a lightguide with different mehtods of heating are presented. The optimal regions of the space of drawing parameters for obtaining a stable lightguide diameter are determined.

An investigation was made of the numerical aperture and excess losses in fiber waveguides with a silicone reflecting cladding at temperatures from –100°C to +20°C. A rapid rise of the optical losses was due to an increase in the refractive index of the silicone cladding because of its crystallization. The use of silicone rubber with a lower crystallization temperature made it possible to extend the working temperature range. Even better results were achieved at low temperatures by the use of waveguides with a core doped with GeO2.

Waveguides were made with a core of anhydrous quartz glass and a cladding of silicone rubber. The glass was formed by electrical melting of high-purity cristobalite. The lowest optical losses in the waveguide at the wavelength 0.98 μ were 20 dB/km rising to 26 dB/km at the wavelength of 0.95 μ. It was found that the hydroxyl group content increased when the glass was drawn into a rod with the aid of a gas burner; however, when drawing was performed using CO2 laser for heating, there was no change in the hydroxyl group content.

A description is given of the technology for making optical fiber waveguides with a quartz-glass core of diameter ~400 μ and polymer cladding. The latter was deposited directly during the drawing of the fiber using heat from a CO2 laser or an oxygen-hydrogen torch. The minimum losses in a waveguide with an excitation aperture of 0.2 were 18 dBAm at 0.8 μ wavelength.