E. Michalski

Growth and properties of potassium holmium double tungstate KHo(WO4)2

Potassium holmium tungstate KHo(WO 4 ) 2 crystal, as other tungstates, shows the high temperature irreversible structural phase transition. Owing to this, KHo(WO 4 ) 2 single crystals were grown due to spontaneous crystallisation with use of the High Temperature Solution Growth technique, which allows to lower the temperature of crystallisation below the temperature of the phase transition. K 2 W 2 O 7 was used as a solvent. It provides a very wide temperature range of crystallisation and does not introduce additional impurities into the melt. The starting flux contained 20 mol% of KHo(WO 4 ) 2 dissolved in K 2 W 2 O 7 . It was found that potassium holmium double tungstate is pleochroic. The two different optical spectra: one spectrum for electrical vector of linearly polarised light parallel to optical Y axis (main spectrum) and second one for electrical vector perpendicular to Y axis were measured.

Optical properties of KGd(WO4)2 single crystals studied by Brillouin spectroscopy

The analysis some of the acoustic phonons propagating in pure and Ho3+-doped KGd(WO4)2 single crystals in the GHz frequency range by Brillouin scattering method has been presented. For investigated crystals the velocities of the longitudinal and transverse acoustic phonons [100], [010], [001], [101], [101] and [110] have been determined. Moreover, the value of elastic constants C22, C44 and C66 of pure and Ho3+-doped KGd(WO4)2 single crystals have been estimated. It was revealed that the presence of the Ho3+-ions in KGd(WO4)2 crystals, for the used doping concentration 1 at% and 8 at%, does not influence their elastic properties. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Crystal Growth Of Mixed Titanium Sillenites

(BGaO) single crystals have been grown, oo. Thermal conditions enabling growth oft uniform [110] sillenite single crystals with totally flat (110) interface have been found. Influence of composition on spectral characteristics of the BTO mixed crystals has been investigated. Keywords: sillenites, BTO, top seeded solution growth, optical absorption (Received November 6, 2002; Accepted May 14, 2002)

Crystal growth and x-ray structure investigation of the KHo(WO4)2

Potassium holmium double tungstate KHo(WO4)2 single crystals with a size of 15x15x25 mm were grown by Top Seeded Solution Growth (TSSG) technique from a K2W2O4 flux. The procedure of the crystal growth was described. The grown crystals were characterized using X-ray diffraction and the unit cell parameters were determined. The obtained data suggest high quality of KHo(WO4)2 single crystals. The refractive indices and optical axes have been determined. The investigations of absorption spectra of KHo(WO4)2 single crystals were performed in a wide spectral range (4000 cm-1 - 40000 cm-1) at temperature range 1.1K up to 300K. The trichroism of KHo(WO4)2 was confirmed experimentally. It means that optical absorption is characterized by three different, independent spectra attributed to three optical axes (so called main optical spectra).© (2003) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

KGW:Yb, Er single crystals growth for eye-safe lasers

KGd(WO4)2 (KGW) single crystals doped with Yb3+, Er3+, and (Yb3+; Er3+) were grown with use of Top Seeded Solution Growth (TSSG) technique. Growth was carried out on oriented seeds from self-flux containing 20 mol% of KGW dissolved in K2W2O7. The spectral properties and laser characteristics of obtained single crystals were investigated. Absorption spectra of Er3+ and Yb3+-doped KGW were measured in the spectral range 200 ÷ 5000 nm at room temperature. Excitation and luminescence spectra were also recorded at room temperature with a JOBIN-YVON spectrofluorimeter using a diode laser (POLAROID 4300, 980 nm, 1 W) as an excitation source. The measurements of the lifetime of the Er3+ and Yb3+ ions in the upper laser level of the samples were made by the direct method with pulse excitation. Investigations of longitudinally pumped KGW:Yb,Er microlasers with various Yb3+ and Er3+ ions concentration, generating at 1.5 μm were carried out.© (2003) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

The magnetic properties of potassium holmium double tungstate

The magnetic investigations of potassium holmium double tungstate KHo(WO4)2 have been performed. The results of measurements of magnetic susceptibility and magnetization as a function of temperature (T from 0.3 K up to 100 K) and magnetic field (up to 1.5 T) are presented. A strong anisotropy of magnetic properties was found. The magnetic measurements data were used to calculate the interaction energy. It was shown that the interactions between nearest neighbors Ho3+ ions have antiferromagnetic character.

Crystal growth and optical properties of iron sillenite Bi25FeO40

Top Seeded Solution Growth (TSSG) technique has been used to produce Bi25FeO40 (BiFeO) single crystals. Thermal conditions enabling growth of uniform [110] sillenite single crystals with flat (110) interface have been found. Spectral characteristics of these single crystals have been investigated. The optical absorption measurements were performed in a broad spectral (IR, VIS and UV) and temperature (3.5 K - 500 K) ranges. The intense source of light was used for coloration of samples. The thermally bleached state was reached after 2 hours annealing at 200°C in the darkness. The optical absorption spectra were shown to be connected with forbidden transitions of Fe3+ ions. The induced absorption is probably due to the polaron center (Fe3++h) similar to that observed in BGO and BSO single crystals.© (2003) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Efficient generation of high-energy picosecond pulses at 355 nm in BiB/sub 3/O/sub 6/

In this paper, we report the generation of high-intensity picosecond pulses in BIBO at 355 nm by using sum frequency generation (SFG) of fundamental pulses at 1064 nm with their second harmonic. The fundamental input pulses were delivered by an amplified mode-locked Nd:YAG laser, providing 35-ps pulses at 1064 nm with energy up to 1 mJ at a repetition rate of 25 Hz in a 2.5-mm beam diameter (EKSMA PL2140). Several BIBO crystals, grown by top-seeded method and of different lengths, were used for the second and third harmonic generation.

The specific heat of potassium holmium double tungstate

The results of measurements of thermal properties (specific heat) of potassium holmium double tungstate KHo(WO4)2 as a function of temperature (from 0.5 to 300 K) and magnetic field (up to 2 T) are presented. The total specific heat without the phonon and Schottky contributions is found to have the anomaly with maximum at T SPT ∼ 5 K. This anomaly is likely related with the structural phase transition (SPT) caused by the cooperative Jahn–Teller effect. The increase of specific heat at very low temperatures and its shift towards high temperatures with increasing magnetic field are observed. The origin of this behaviour can be connected with possible magnetic phase transition induced by magnetic field.

Physical properties of potassium erbium double tungstate KEr(WO4)2

The paper presents the results of complex investigations of the potassium-erbium double tungstate. The following properties have been measured: specific heat, specific heat in magnetic field, thermal expansion, thermal expansion in magnetic field, magnetization and X-ray structural data, reflectance and optical absorption spectra. The experiments were performed in the broad temperature range from 0.4 K to 300 K, spectral range from 4000 cm-1 to 40000 cm-1 and magnetic field up to 10T. The magnetic phase transition was found at temperature T=0.84K. In thermal expansion experiment the strong anomaly was found at T=7.6 K in magnetic field 10T. The KEr(WO4)2 belongs to the optical class of biaxial and pleochroic (trichroic) crystals. Using spectroscopy methods, the orientation of optical axes and refractive indices have been found. The main optical absorption spectra have been measured. The temperature dependence of optical absorption was determined.