Putcha Venkateswarlu

Short-pulsed stimulated emission in the powders of NdAl 3 (BO 3 ) 4 , NdSc 3 (BO 3 ) 4 , and Nd:Sr 5 (PO 4 ) 3 F laser crystals

Short (>300-ps) pulses of stimulated emission were found from powders of NdAl3(BO3)4, NdSc3(BO3)4, and Nd:Sr5(PO4)3F laser crystals during 532- and 805-nm excitation. Study of stimulated emission in the mixture of two powders has shown that the different components influence each other. That implies a collective behavior of emitting particles. The main features of experimentally observed stimulated emission are described with a simple model accounting for 4F3/2 excited-state concentration and emission energy density. The threshold of stimulated emission in powders is shown to be inversely proportional to the small-signal amplification along the photon path in the pumped volume.

Optical characterization of Mn:YAlO 3 : material for holographic recording and data storage

Photoinduced coloration and the holographic grating recording associated with it are experimentally studied in Mn-doped yttrium orthoaluminate (Mn:YAlO3). High diffraction efficiency is demonstrated in visible and in infrared light. The diffraction efficiency at 514.5 nm exceeds 50%. The strong energy exchange between the writing beams observed in a two-wave mixing experiment suggests that diffraction in Mn:YAlO3 is due to mainly nonlocal holographic effect and an electro-optical effect. Mn:YAlO3 is shown to be a promising material for holographic recording and optical storage.

Two-step upconversion luminescence in Yb:Tb:YSGG crystal

Multiline upconversion luminescence ranging from 375 to 635 nm was studied in Yb:Tb:YSGG crystal, a possible candidate for a tunable upconversion laser material. This luminescence was attributed to the transitions starting from the 5D3 and 5D4 excited levels of Tb. Two sequential steps in the upconversion were determined: at the first step Yb–Tb cooperative upconversion and cooperative absorption populate level 5D4, and at the second step interaction of excited Yb and Tb (in the 5D4 state) ions populates level 5D3. At 500-mW Ti:sapphire pumping, the excited-state concentration of Tb ions exceeded 2% of Yb excited-state concentration.

Color-center powder laser: the effect of pulverization on color-center characteristics

Stimulated emission is obtained and characterized in a powder of LiF crystal with color centers. Absorption, luminescent, and kinetics properties of color centers are studied in powder samples of LiF. They are found to be rather different from those in a bulk material. The difference is explained by dislocations mechanically created during the pulverization of the material. The characteristics of stimulated emission in LiF powder samples were found very different from those in scattering Nd-doped luminophosphors. This difference can be ascribed to a much higher emission cross section and a much smaller lifetime of emitting centers in LiF.

Four-photon-mixing-mediated stimulated Raman scattering in a multimode optical fiber

Stimulated Raman scattering with 532-nm pulsed laser light is investigated in a 7.9-microm-core step-index multimode fiber. While low-intensity pump or single-mode LP(01) excitation produces the usual stimulated Raman scattering light, mixed-mode (LP(01) + LP(02)) excitation with pump intensities of ~5 kW uniformly shifts the multiorder Stokes Raman spectrum by an amount determined by fiber parameters, thus making stimulated Raman scattering tunable. This is due to the mediating influence of the four-photon mixing in the fiber.

Laser beam collimation using a phase conjugate Twyman-Green interferometer

This paper presents an improved technique for testing laser beam collimation using a phase conjugate Twyman-Green interferometer. The technique is useful for measuring laser beam divergence. It is possible using this technique to detect the defocusing of the order of one micrometer for a well corrected collimating lens. A relation is derived for the defocusing that can be detected by the phase conjugate interferometer.

Measurement of birefringence of optical materials using a wedged plate interferometer

A nondestructive technique for measuring the birefringence of optical materials such as calcite using wedged plate interferometer is presented. The sample needed for measuring the refractive index must be polished in the form of a parallel plate. The method is based on the measurement of the longitudinal displacement of the focus when the parallel plate is inserted in a converging beam of light. The displacement of the focus is a measure of the refractive index of the optical material. In the case of a uniaxial crystal, the displacement of the focus for the extraordinary ray is different from the displacement of the focus for the ordinary ray. Hence the birefringence of the crystal is determined by measuring the difference between the two focii. It is possible to obtain an accuracy up to 0.0002 in the measurement of birefringence depending on the sample thickness. The method should find its application for the characterization of new crystals in various material research and crystal growth laboratories.

Penning type of ionizing energy transfer collisions in a Hg-Ar discharge detected by the optogalvanic effect

Abstract The temporal evolution of the optogalvanic signals have been investigated in detail in a Hg-argon discharge by irradiating it with an excimer pumped dye laser. The signals at 4510.7, 4596 and 4628.4 A exhibited anomalous behaviour. Analysis of the data revealed that the excited Ar and Hg atoms respectively in the 1 P 1 and 3 P 1 states participated in energy transfer collisions, causing atomic mercury to excite to an ionized energy state, while simultaneously the argon atom relaxes to its ground state.

Laser beam collimation using Talbot interferometry

A modified method of checking laser beam collimation by using Talbot interferometry coupled with a moir6 phenomenon is described.

Optogalvanic effect in neon hollow cathode discharge

Abstract About 300 transitions have been recorded in the optogalvanic spectrum of neon in the visible wavelength region 410–670 nm by axially irradiating a hollow cathode discharge with an excimer pumped dye laser. Several weak lines have been recorded including the 632.8 nm neon laser wavelength. Temporal evolution of the optogalvanic signals was studied at several wavelengths. An explanation is given for the occasional absence of correlation in intensities observed in optogalvanic effect with those measured in emission. An explanation is also given for the voltage dependent polarity changes of optogalvanic signals. Energy transfer collisions were also detected in iron-neon discharge.