Anirban Mitra

Photoluminescence and ultraviolet laser emission from nanocrystalline ZnO thin films

We report on photoluminescence and ultraviolet laser emission from ZnO pellets and thin films of ZnO. Laser emission from disordered polycrystalline thin films and pellets was observed in all directions. ZnO films were deposited on glass substrate at room temperature in various ambient gas pressures of oxygen using the pulsed laser deposition technique. The dependence of laser emission on the size of nanocrystallites observed at different pressures of ambient gas is discussed. Photoluminescence spectra depend on the stoichiometry and the microstructure of the film.

Synthesis and characterization of ZnO thin films for UV laser

We report on deposition of zinc oxide thin films on glass substrate at room temperature in ambient oxygen pressure ranging from 10 mTorr to 1 Torr by pulsed laser deposition. As grown polycrystalline thin films were optically pumped to investigate the dependence of laser action and photoluminescence (PL) on stoichiometry and microstrucure of the films. The intensity of the laser emission increases with thickness of the film and depends on the size of nano-crystallites. Films deposited at pressures lower than 300 mTorr showed better morphology, stoichiometry and adhesion quality. X-ray diffraction, atomic force microscopy, Rutherford back scattering and PL techniques were used to characterize as grown films.

DIAGNOSTICS OF LASER ABLATED PLASMAS USING FAST PHOTOGRAPHY

We report on dynamics of the laser ablated plumes in an ambient atmosphere using fast photography. The expanding plasma is studied at different delay times with respect to the ablating pulse. Dependence of plasma parameters such as velocity, temperature, density, and pressure on time and ambient atmosphere is presented. The images of the expanding plume are used to estimate the size of the particles in the plume.

Room-temperature ultraviolet luminescence from γ-CuCl grown on near lattice-matched silicon

We have probed the luminescence properties of a wide-band-gap, direct band-gap optoelectronic material, grown on closely lattice-matched silicon substrates, namely, γ-CuCl on Si. This material system is compatible with current Si or GaAs-based electronic/optoelectronic technologies. Polycrystalline epitaxy of CuCl can be controlled such that it maintains an orientation similar to the underlying Si substrate. Importantly, chemical interactions between CuCl and Si are eliminated. Photoluminescence and cathodoluminescence results for CuCl, deposited on either Si (100) or Si (111), reveal a strong room-temperature Z3 excitonic emission at ∼387nm. We have developed and demonstrated the room-temperature operation of an ultraviolet electroluminescent device fabricated by the growth of γ-CuCl on Si. The application of an electrical potential difference across the device results in an electric field, which promotes light emission through hot-electron impact excitation of electron-hole pairs in the γ-CuCl. Since th...

Laser ablation of human tooth

We report the measurements of ablation threshold of human tooth in air using photo-thermal deflection technique. A third harmonic (355nm) of Nd:YAG (yttrium aluminum garnet) laser was used for irradiation and a low power helium neon laser as a probe beam. The experimental observations of ablation threshold in conjunction with theoretical model based on heat conduction equations for simulating the interaction of a laser radiation with a calcified tissue are used to estimate the absorption coefficient of human tooth.

ULTRAVIOLET LASER EMISSION FROM OPTICALLY PUMPED ZnO

We report UV laser emission from an optically pumped zinc oxide powder. The laser emission spectra depend on the angle of observation which is random. The lasing is attributed to coherent feedback due to recurrent light scattering in the powder.

Determination of laser ablation threshold of Teflon at different harmonics of Nd:YAG laser using photothermal deflection technique

We report the measurement of the laser ablation threshold of Teflon using photothermal beam deflection at 1.06 μm, 0.532 μm, and 0.355 μm irradiation in air. The measured ablation threshold at various wavelengths is used to estimate the absorption coefficient. It is observed that the absorption coefficient increases with a decrease in wavelength.

Sub Nanosecond Pulse Generation by Stimulated Brillouin Scattering using FC-75 in an Integrated Setup with Laser Energy up to 1.5 J

We have demonstrated the short pulse generation of Nd:YAG laser at the fundamental wavelength by using stimulated Brillouin scattering (SBS) in liquid FC-75 at the energy of 1.5 J with a compact single set-up consists of generator and amplifier. Minimum pulse width obtained without attenuator and with attenuator are 770 ps and 600 ps respectively. SBS Conversion efficiencies are 90% without attenuator and 55% with attenuator. The brightness of the compressed pulse was about twelve fold higher than that of incident pulse.

DEPENDENCE OF SECOND HARMONIC GENERATION ON SIZE OF NANOCRYSTALLITES OF ZnO

We report second harmonic generation (SHG) from ZnO thin films deposited by the pulsed laser deposition technique at ambient oxygen pressures ranging from 10 mTorr to 1 Torr on glass substrate at room temperature (RT). The dependence of SHG on grain size and thickness of the film is discussed.

In-Plane and Out-of-Plane Plasmons in Random Silver Nanoisland Films

Effective permittivity of closely spaced random nanoparticles supported by a substrate has been calculated using a modified Yamaguchi’s model (MYM) which involves the exact expression of a local field outside a metal nanoparticle (NP) along with the effective-medium approach. Pulsed laser deposition has been used to deposit silver nanoisland films on SiO2 substrates. In-plane and out-of-plane plasmonic responses have been calculated using MYM for various filling fractions and the results are compared with those obtained from spectroscopic ellipsometry. Distinct features of out-of-plane and in-plane plasmons are observed with an spectroscopic ellipsometer and their behavior is supported by the present theoretical investigation. The comparison of the effective dielectric constants of the films obtained from ellipsometry data with those calculated using MYM shows uniaxial optical anisotropy in our case. The calculated morphological parameters (filling fraction, aspect ratio, and average particle size) using MYM are also found to be consistent with those obtained from FESEM images.