P. Venkateswarlu

INFRARED TO VISIBLE ENERGY UPCONVERSION IN ER3+-DOPED OXIDE GLASS

Intense green emission was observed at room temperature from the 4S3/2 level of Er3+ doped in a multielement oxide glass when its 4I9/2 level was resonantly excited with a near‐infrared laser beam of 797 nm. Our studies indicate that energy transfer and excited state absorption are responsible for the generation of upconverted green emission from the sample. The upconversion efficiency is found to be 0.14%.

Site-selective energy upconversion in CaF 2 :Ho 3+

From the absorption spectrum of CaF2:Ho3+, Judd–Ofelt intensity parameters were estimated as Ω2=0.018×10-20 cm2, Ω4=0.57×10-20 cm2, and Ω6=0.587×10-20 cm2. Radiative transition probabilities and radiative lifetimes were also estimated for some of the levels. We observed red-to-green, -blue, and -violet energy upconversion in CaF2:Ho3+ with efficiencies of 0.08%, 0.13% and 1.35×10-3%, respectively, on resonant excitation of the 5F5 state. Under site-selective excitation we also found that the blue-upconversion signal intensity was approximately three times larger than that of the green-upconversion signal intensity. On resonantly exciting the 5I4 state we detected strong green upconversion signals from the 5S2 state and found that excited-state absorption from 5I7 was responsible for this process. Upconversion efficiency of the process was determined to be 8.1%. On resonantly exciting the 5I5 state, we detected strong red emission in CaF2:Ho3+ and strong green emission in LaF3:Ho3+. Such a host-dependent upconversion frequency emission is also explained.

Near-infrared-to-blue energy upconversion in LaF 3 :Ho 3+

When the 5F5 levels of Ho3+ in LaF3 were resonantly excited with a red dye laser beam of 640 nm, blue and green emissions were detected from the 5G5, the 5F3, and the 5S2(5F4) levels at 416, 485, and 546 nm, respectively. We found that excited ions in the 5F5 state undergo nonradiative relaxation to the 5I6 state and are then upconverted to the 5G5 state by the absorption of a second photon, as well as by energy-transfer interaction. The upconversion efficiency into the 5F3 state was estimated as ~1.1 × 10−4. We also observed energy-upconverted emissions from the 5F3 and the 5S2 levels when the material was excited with an 800-nm near-infrared laser. The absorption of a second laser photon from the 5I6 state was found to be responsible for the upconverted green emission.

Reflection holographic gratings in [111] cut Bi12TiO20 crystal for real time interferometry

Abstract It is shown that reflection grating in [111] Bi12TiO20 crystal can be used for dynamic interferometry with a low power HeNe laser, giving a diffraction efficiency of 0.14%. Predicted and confirmed is the possibility of hologram recording by orthogonal polarized waves, using as advantage natural optical activity.

Crystal growth, spectroscopic characterization, and laser performance of a new efficient laser material Nd:Ba5(PO4)3F

High quality single crystals of neodymium doped barium fluorapatite have been grown by the Czochralski technique and evaluated as an optical gain medium. A product of the emission cross section and lifetime of Nd3+ luminescence of more than 1.8×10−22u2009cm2u2009s at 1055 nm, and laser performance with slope efficiency up to 65% have been obtained.

High resolution study of the E(0+g) → B3Π (0+u) transition (4400-4000 Å) of I2

Abstract The E → B transition of I 2 in the region 4400-4000 A has been studied under high resolution using a 7.3 m vacuum Ebert spectrograph in the 14th order. The values of the constants B e , α e , γ e , D e and β e of both E and B states determined from the analysis of the rotational structure of nine bands of the system are presented. Vibrational constants of the E state obtained from the analysis of all the bands so far reported and consistent with the precise constants of the B state given in previous work are also presented. The origin of the upper state, E (0 + g ), of the transition is discussed.

Optical branching in dye-doped polymeric waveguide

We demonstrate theoretically and experimentally that a single optical beam splits into multiple beams (branches) as a result of light induced permanent refractive index decrease in a dye-doped polymeric slab waveguide upon its upconverted photobleaching. The input Gaussian beam initially splits into two primary branches that grow in time moving out of the central axis and eventually collapse into numerous secondary branches. The proposed theoretical model is nonlocal in time and is based on a Shrodinger-type nonlinear propagation equation complemented by a rate equation for the decrease of the refractive index.

Photoinduced Electric Current in Fe-Doped KNbO3

Photorefractive KNbO3:Fe is characterized by monitoring of the electric currents induced in the crystal that are due to applied illumination. Important photorefractive parameter values, such as the Maxwell relaxation time, carrier-diffusion length, carrier-screening length, and the magnitude of the photogalvanic current are thereby estimated.

Vanishing optical isolation barrier in double ion‐implanted lithium niobate waveguide

Isolation properties at different propagation directions have been studied for an optical barrier between two superposed planar waveguides produced by MeV He+ implantation in LiNbO3. The barrier exists while the modes of the double structure propagate along the optic axis. The spacing between the modes measured with a prism coupler features efficiently isolated waveguides. The barrier ‘‘vanishes’’ when the directional angle between an extraordinary wave and the optic axis exceeds 50°. In this case the mode spacing shows strong coupling between the waveguides that makes the double structure similar to a single waveguide with double thickness.

Optical phase-conjugate studies of organic dyes doped in a boric acid host

Nonlinear optical studies of Dichlorofluorescein, Arcridine Yellow, 4-(Dicyanomethylene)-2-methyl-6-(p-dimethylaminostyryl)-4H-pyran, Rhodamine 110, and Pyridine-1 dyes doped in a boric acid host have been studied at Ar+ laser wavelengths. Excited-state absorption was demonstrated directly by use of the pump–probe technique. Ground- and excited-state absorption cross sections and saturation intensities, phase-conjugate reflectivities, grating formation, and decay times were measured for all dyes. Phase-conjugate signals of Pyridine-1 exhibited oscillatory behavior in time, which was found to be due to heat produced during the nonradiative relaxation of the excited molecules. Third-order susceptibilities were also estimated for the dye-doped samples from the saturation measurements. The parameters derived from the saturation data are used to predict phase-conjugate reflectivities and are compared with the measurements.