Characteristic properties of ZnO random laser pumped by nanosecond pulses

Investigations of UV radiation spectra of powdered zinc oxide and its unordered film were conducted. The samples were pumped by 3-rd harmonics of the two-stage Nd:YAG-laser (λ=355 nm) with pulse duration ∼10 ns. Maximum density of energy of pumping pulses was about 150 mJ/cm². With some of our samples, we achieved lasing. The threshold values of the pumping energy density occurred higher than those under picosecond pumping approximately for one-two orders of magnitude. It was shown that the threshold of lasing and the character of lasing spectra depend on the morphology of particles forming a powder. The long-wavelength shift of the maximum of lasing spectra with a rise of the pumping was observed. It was interpreted as a result of participation of electron–hole plasma recombination in the process of lasing. A chaotic character of lasing spectra was observed and partially analyzed. PACS 42.55.Zz; 78.55.Et; 42.70.Hj     

Studies on photoinduced effects in pulse-electrodeposited Ag/Hg-1212/CdSe hetero-nanostructures

Metal/superconductor/semiconductor (Ag/Hg-1212/CdSe) hetero-nanostructures have been fabricated using pulse-electrodeposition technique and are characterized by X-ray diffraction (XRD), full-width at half-maximum (FWHM) and scanning electron microscopy (SEM) studies. The junction capacitance of Ag/Hg-1212, Hg-1212/CdSe and Ag/Hg-1212/CdSe heterojunctions is measured in dark and under laser irradiation at room temperature. The nature of the junction formed and built-in-junction potentials were determined. The increase in carrier concentration across the junction due to photo-irradiation has been observed.     

Degree of coherence and dimensions of the generation region of powder lasers

A degree of coherence of powder-laser radiation of 10–20% is estimated by the magnitude of the image contrast for a speckle, although cases are recorded where it attains 40–50%. It is found that as the average speckle intensity increases, the contrast decreases. It is established that the minimum, dimensions of the generation region in powders are 20–30 μm. Cases of existence of several generation centers simultaneously are noted. An attempt to interpret the results obtained is made. Institute of Radio Engineering and Electronics, Russian Academy of Sciences, 11, Mokhovaya St., Moscow, 103907. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 65, No. 5, pp. 780–786, September–October, 1998.     

Effect of laser irradiation of C-V characteristics of electrodeposited Ag/Tl-2223/CdSe hetero-nanostructures

One of the innovative technological directions for the high-temperature superconductors has been persued by fabricating the heteroepitaxial multilayer structures such as superconductor-semiconductor heterostructures. In the present investigation, metal/superconductor/semiconductor (Ag/Tl-2223/CdSe) hetero-nanostructures have successfully been fabricated using dc electrodeposition technique and were characterized by X-ray diffraction (XRD), full-width at half-maximum (FWHM) and scanning electron microscopy (SEM) studies. The measurement of junction capacitance as a function of biasing voltage was used for the estimation of junction built-in-potential (V _D) and to study the charge distribution in a heterojunction. The Mott-Schottky plots were measured for each junction in dark and under the photo-irradiation. The effect of laser irradiation on C-V characteristics of hetero-nanostructure has been studied.     

Electronic-vibrational spectra of nonequivalent europium luminescence centers in lanthanide oxides

Journal of Applied Spectroscopy -     

ZnO lasing in complex systems with tetrapods

A ZnO structure in the form of a core–shell wire was grown with a modified vapour transport and condensation method. The wire consists of a dense core which may play the role of a waveguide and a shell formed mainly from tetrapod-type crystallites. The high optical quality of the produced ZnO material is confirmed by continuous wave photoluminescence (PL) analysis demonstrating that low- temperature PL is related to the recombination of bound excitons, while room-temperature PL is due to free excitons. Good quality of the crystal structure is demonstrated also by the Raman spectrum. The shell of the wire exhibits room-temperature laser action due to lasing modes in tetrapods under the excitation by nanosecond laser pulses. The nature of the lasing modes is discussed. A simplified model for one of the possible modes is suggested.     

Quasi-whispering gallery modes in ZnO microtowers

We show that the laser spectra of ZnO films composed of particles that look like microtowers represent two bands with practically constant spectral distances between their peaks. By numerical analysis, we show that these two bands are due to whispering gallery modes (WGM), and one of these bands corresponds to the quasi-whispering gallery mode. Thus, we obtain here the first clear demonstration of the existence of quasi-WGMs, and show, in addition, that the width of the bands is caused by random spread of sizes of the ZnO particles in the lasing part.