253 research outputs found

    Frequency-Doubling of Femtosecond Pulses in “Thick” Nonlinear Crystals With Different Temporal and Spatial Walk-Off Parameters

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    We present a comparative study on frequency-doubling characteristics of femtosecond laser pulses in thick nonlinear crystals with different temporal and spatial walk-off parameters. Using single-pass second harmonic generation (SHG) of 260 fs pulses at 1064 nm from a high-average-power femtosecond Yb-fiber laser in 5-mm-long crystals of β-BaB2O4 (BBO) and BiB3O6 (BIBO), we find that for comparable values of temporal and spatial walk-off parameters in each crystal, the optimum focusing condition for SHG is more strongly influenced by spatial walk-off than temporal walk-off. It is also observed that under such conditions, the Boyd and Kleinman theory commonly used to define the optimum focusing condition for frequency-doubling of cw and long-pulse lasers is also valid for SHG of ultrafast lasers. We also investigate the effect of focusing on the spectral, temporal, and spatial characteristics of the second harmonic (SH) radiation, as well as angular acceptance bandwidth for the SHG process, under different temporal and spatial walk-off conditions in the two crystalsPeer ReviewedPostprint (author's final draft

    Stable, High-Average-Power, Degenerate Optical Parametric Oscillator at 2.1 ÎĽm

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    We describe a degenerate 1.064-ÎĽm-pumped pulsed optical parametric oscillator based on MgO:PPLN in compact Littrow-grating cavity configuration, providing 2.7W of average power at 2.1ÎĽm with high spectral and power stability in good spatial beam quality.Peer ReviewedPostprint (author's final draft

    A Hybrid Filter with Impulse Detection for Removal of Random Valued Impulse Noise from Colour Videos

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    This paper presents a three dimensional hybrid filter to remove random valued impulse noise from colour video sequences. The switching median technique is utilized to protect noise free isolated pixels from filtering so as to avoid blurring of frames. The restoration of noisy pixels is done by brightness information obtained from median filtering and chromaticity information is obtained from vector directional filtering. This hybrid filter is applied in three dimensional sliding window where spatial as well as temporal information about neighbourhood is available for restoration of frame under consideration. Only noise free pixels of three dimensional sliding window are used for restoration of frame under consideration. Simulation results show that the proposed three dimensional hybrid filter yields superior performance in comparison to other filtering method

    Fiber-laser-based, green-pumped, picosecond optical parametric oscillator using fan-out grating PPKTP

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    We report a stable, Yb-fiber-laser-based, green-pumped, picosecond optical parametric oscillator (OPO) for the near-infrared based on periodically poled potassium titanyl phosphate (PPKTP) nonlinear crystal, using fan-out grating design and operating near room temperature. The OPO is continuously tunable across 726–955 nm in the signal and 1201–1998 nm in the idler, resulting in a total signal plus idler wavelength coverage of 1026 nm by grating tuning at a fixed temperature. The device generates up to 580 mW of average power in the signal at 765 nm and 300 mW in the idler at 1338 nm, with an overall extraction efficiency of up to 52% and a pump depletion >76%>76%. The extracted signal at 765 nm and idler at 1746 nm exhibit excellent passive power stability better than 0.5% and 0.8% rms, respectively, over 1 h with good beam quality in TEM00TEM00 mode profile. The output signal pulses have a Gaussian temporal duration of 13.2 ps, with a FWHM spectral bandwidth of 3.4 nm at 79.5 MHz repetition rate. Power scaling limitations of the OPO due to the material properties of PPKTP are studied.Peer ReviewedPostprint (author's final draft

    Optical parametric generator based on orientation-patterned gallium phosphide

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    We report the first pulsed optical parametric generator based on Orientation-patterned Gallium Phosphide. The output is tunable from 1721-1850 nm (signal) and 2504-2787 nm (idler), providing a total output power of 18 mW.Peer ReviewedPostprint (author's final draft

    Formulation of Glipizide Time-Controlled Release Tablets By Press Coating Using Hydrophilic and Hydrophobic Polymers – Its In Vitro Dissolution, Time Lag and Kinetic Models

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    The main aim of the work is to achieve time-controlled disintegration with distinct predetermined time lag. To study the effect of formulation of outer shell comprising both hydrophobic polymer and hydrophilic excipients on the time lag of drug release. To find out the suitable weight ratios of hydrophilic excipients, to modulate the time lag of time controlled disintegrating tablets. Studies were under taken on the formulation of glipizide time controlled release tablets by press coating using hydrophilic polymers polyethylene glycol (PEG 6000) and hydroxyl ethyl cellulose (HEC) and hydrophobic polymer ethylcellulose. Here EC/PEG was used in the outer coating layer for E1 formulation and EC/HEC in outer coating layer for E2 formulation. The order of dissolution of glipizide from E1 and E2 formulations Chemical incompatibilities study confirmed that there is no interaction between drug and excipients in the formulation. The weight variations, drug content uniformity, hardness, friability of all the formulated tablets were within the specified requirements. Drug release kinetics confirmed that the glipizide time controlled release formulations were best expressed by Higuchi’s equation. In conclusion, the time lag of press-coated tablet could be modulated by choosing the type and amount of excipient used in the outer shell to achieve the time-controlled disintegration according to the time required The present st tablet can be suitably modulated by formulating the outer shell with ethyl cellulose and polyethylene glycol 6000 or hydroxyl ethyl cellulose

    Phase-Modulation-Mode-Locked Continuous-Wave MgO:PPLN Optical Parametric Oscillator

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    We report phase-modulation mode-locking of a continuous-wave (cw) singlyresonant optical parametric oscillator (OPO) in the near- and mid-infrared based on MgO-doped periodically poled LiNbO3 (MgO:PPLN) and pumped by an Yb-fiber laser at 1064 nm. By investigating the spectral output and pulse formation characteristics of the OPO, we observe a clear transition from an unstable spectrum in cw operation to a stable and smooth profile under phase modulation, confirming mode-locked operation. Pulse generation and spectral characteristics under different operating conditions are studied, including the effects of the location of the intracavity phase modulator and the number of oscillating modes on mode-locked output pulse duration.Peer ReviewedPostprint (published version
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