Kavita Devi

Extension of VIKOR method in intuitionistic fuzzy environment for robot selection

Abstract Decision making is the process of finding the best option among the feasible alternatives. In classical multiple-criteria decision making methods, the ratings and the weights of the criteria are known precisely. However, if decision makers are not able to involve uncertainty in the defining of linguistic variables based on fuzzy sets, the intuitionistic fuzzy set theory can do this job very well. In this paper, VIKOR method is extended in intuitionistic fuzzy environment, aiming at solving multiple-criteria decision making problems in which the weights of criteria and ratings of alternatives are taken as triangular intuitionistic fuzzy set. For application and verification, this study presents a robot selection problem for material handling task to verify our proposed method.

High-efficiency, multicrystal, single-pass, continuous-wave second harmonic generation

We describe the critical design parameters and present detailed experimental and theoretical studies for efficient, continuous-wave (cw), single-pass second harmonic generation (SHG) based on novel cascaded multicrystal scheme, providing >55% conversion efficiency and multiwatt output powers at 532 nm for a wide range of input fundamental powers at 1064 nm. Systematic characterization of the technique in single-crystal, double-crystal and multicrystal schemes has been performed and the results are compared. Optimization of vital parameters including focusing and phase-matching temperature at the output of each stage is investigated and strategies to achieve optimum SHG efficiency and power are discussed. Relevant theoretical calculations to estimate the effect of dispersion between the fundamental and the SH beam in air are also presented. The contributions of thermal effects on SHG efficiency roll-off have been studied from quasi-cw measurements. Using this multicrystal scheme, stable SH power with a peak-to-peak fluctuation better than 6.5% over more than 2 hours is achieved in high spatial beam quality with M2<1.6.

Multicrystal, continuous-wave, single-pass second-harmonic generation with 56% efficiency

We report a simple and compact implementation for single-pass second-harmonic-generation (SP-SHG) of cw laser radiation, based on a cascaded multicrystal (MC) scheme, that can provide the highest conversion efficiency at any given fundamental power. By deploying a suitable number of identical 30-mm-long MgO:sPPLT crystals in a cascade and a 30W cw Yb-fiber laser at 1064nm as the fundamental source, we demonstrate SP-SHG into the green with a conversion efficiency as high as 56% in the low-power as well as the high-power regime, providing 5.6W of green output for 10W and 13W of green output for 25.1W of input pump power. The MC scheme permits substantial increase in cw SP-SHG efficiency compared to the conventional single-crystal scheme without compromising performance with regard to power stability and beam quality.

High-power, continuous-wave, single-frequency, all-periodically-poled, near-infrared source

We report a high-power, single-frequency, continuous-wave (cw) source tunable across 775-807 nm in the near-infrared, based on internal second harmonic generation (SHG) of a cw singly-resonant optical parametric oscillator (OPO) pumped by a Yb-fiber laser. The compact, all-periodically-poled source employs a 48-mm-long, multigrating MgO doped periodically poled lithium niobate (MgO:PPLN) crystal for the OPO and a 30-mm-long, fan-out grating MgO-doped stoichiometric periodically poled lithium tantalate (MgO:sPPLT) crystal for intracavity SHG, providing as much as 3.7 W of near-infrared power at 793 nm, together with 4 W of idler power at 3232 nm, at an overall extraction efficiency of 28%. Further, the cw OPO is tunable across 3125-3396 nm in the idler, providing as much as 4.3 W at 3133 nm with >3.8  W over 77% of the tuning range together with >3  W of near-infrared power across 56% of SHG tuning range, in high-spatial beam-quality with M2<1.4. The SHG output has an instantaneous linewidth of 8.5 MHz and exhibits a passive power stability better than 3.5% rms over more than 1 min.

Single-frequency, high-power, continuous-wave fiber-laser-pumped Ti:sapphire laser

We demonstrate a high-power, continuous-wave (cw), single-frequency green source based on single-pass second-harmonic generation of a Yb-fiber laser in MgO:sPPLT as a viable pump source for a cw single-frequency Ti:sapphire ring laser. By careful design and optimization, the Ti:sapphire laser can provide as much as 2.3 W of cw single-frequency output across a 47 nm tuning range, limited by the reflectivity of the cavity mirrors. By implementing active stabilization of the laser frequency to an external reference, an ultrastable Fabry-Perot interferometer, we obtain a frequency stability better than 12 MHz over 10 min and continuous tunability greater than 180 MHz. Stable output power with peak-to-peak fluctuation of 5.4% over 75 min, in high spatial beam quality with M(2)<1.34, is achieved.

Ultrafast optical vortex beam generation in the ultraviolet

We report on the generation of ultrafast vortex beams in the deep ultraviolet (DUV) wavelength range at 266 nm, for the first time to our knowledge. Using a Yb-fiber-based green source in combination with two spiral phase plates of orders 1 and 2, we were able to generate picosecond Laguerre-Gaussian (LG) beams at 532 nm. Subsequently, these LG beams were frequency doubled by single-pass, second-harmonic generation in a 10 mm-long β-BaB2O4 crystal to generate ultrafast vortex beams at 266 nm with a vortex order as high as 12, providing up to 383 mW of DUV power at a single-pass, green-to-DUV conversion efficiency of 5.2%. The generated picosecond UV vortex beam has a spectral width of 1.02 nm with a passive power stability better than 1.2% rms over >1.5  h.

Tunable, continuous-wave, ultraviolet source based on intracavity sum-frequency-generation in an optical parametric oscillator using BiB 3 O 6

We report a continuous-wave (cw) source of tunable radiation across 333-345 nm in the ultraviolet (UV) using bismuth triborate, BiB₃O₆ (BIBO) as the nonlinear gain material. The source is based on internal sum-frequency-generation (SFG) in a cw singly-resonant optical parametric oscillator (OPO) pumped at 532 nm. The compact tunable source employs a 30-mm-long MgO:sPPLT crystal as the OPO gain medium and a 5-mm-long BIBO crystal for intracavity SFG of the signal and pump, providing up to 21.6 mW of UV power at 339.7 nm, with >15 mW over 64% of the SFG tuning range. The cw OPO is also tunable across 1158-1312 nm in the idler, delivering as much as 1.7 W at 1247 nm, with >1W over 65% of the tuning range. The UV output at maximum power exhibits passive power stability better than 3.4% rms and frequency stability of 193 GHz over more than one minute.

Stable, continuous-wave, ytterbium-fiber-based single-pass ultraviolet source using BiB3O6.

We report stable continuous-wave (CW) ultraviolet (UV) generation at 354.7 nm using single-pass sum-frequency-generation (SFG) of a CW Yb-fiber laser at 1064 nm in the nonlinear crystal, BiB3O6. The 532 nm radiation is obtained by single-pass second-harmonic generation of the Yb-fiber laser in a 30-mm-long MgO:sPPLT crystal. Using a 10-mm-long BiB3O6 crystal for SFG, with a measured angular acceptance bandwidth of 0.57 mrad, we generate as much as 68 mW of CW single-frequency UV radiation with a passive power stability better than 3.2% rms over 2 h and frequency stability better than 436 MHz over 2.5 h. The UV output beam has a TEM00 spatial profile with M(x)(2)<1.6 and M(y)(2)<1.8.

Mode-locked, continuous-wave, singly resonant optical parametric oscillator

We report an actively mode-locked continuous-wave (cw) optical parametric oscillator in singly resonant oscillator (SRO) configuration, generating stable 230 ps pulses at 80 MHz repetition rate. The idler-resonant cw SRO, configured in standing-wave cavity, is based on MgO:sPPLT as the nonlinear gain material and pumped at 532 nm. Mode-locking is achieved by direct deployment of an intracavity phase modulator close to one of the SRO cavity end mirrors. The effects of modulation depth and modulation frequency on mode-locked pulse duration and repetition rate are investigated for both idler and signal pulses. Mode-locking is further confirmed by enhancement of single-pass second-harmonic generation of SRO output in the crystal of β-BaB(2)O(4).

Frequency-modulation-mode-locked optical parametric oscillator

Using a continuous-wave doubly-resonant optical parametric oscillator, we demonstrate, for the first time, the successful deployment of a phase modulator in combination with an antiresonant ring interferometer for generation of mode-locked pulses.