NOPR Collection:

Effect of facet coatings on laser diode characteristics

2010-06-05T16:30:49Z

Title: Effect of facet coatings on laser diode characteristics Authors: Bhore, P V; Shah, A P; Gokhale, M R; Ghosh, S; Bhattacharya, A; Arora, B M Abstract: The cleaved facets of semiconductor diode lasers act like mirror. Mirror coatings are applied to change the reflectivity and passivate the surfaces. Design of antireflection coating is optimized for single layer of Al₂O₃and high reflection coating is optimized for stacks of Al₂O₃and Si Bragg reflector. Electron beam evaporation has been used to deposit uniform Al₂O₃/Si film under high vacuum with pressure 10^-6mbar and temperature 150-160°C. The optimization of experimental parameters for the dummy GaAs substrate has been discussed. Using these parameters laser facets were coated and changes in the L-I characteristics have been measured and investigated step by step. The output light power versus current characteristics of coated laser diode is compared with that of uncoated one for its characterization under pulsed conditions and have shown that the facet reflectivity has played a major role in determining threshold current density of semiconductor laser. Page(s): 438-440

Theoretical approach to the tunneling mechanoluminescence produced during cleavage of II-VI semiconductors

2010-06-03T16:31:10Z

Title: Theoretical approach to the tunneling mechanoluminescence produced during cleavage of II-VI semiconductors Authors: Choudhary, Vibha; Singh, Anubha; Chandra, V K; Gupta, R K; Chandra, B P Abstract: This paper describes the tunneling mechanoluminescence (ML) produced during fracture of II-VI semiconductors. The electric potential surrounding the charged dislocations bends, valence band and conduction band strongly and consequently, the electron centres float up in synchronism with the band bending as the dislocations core approaches starting distance from the dislocation core the process of electron tunneling from the centre into the conduction band becomes significant. Thus, a moving dislocation can transfer electrons form deep traps to the conduction band. These electrons subsequently recombine with the holes at impurity centres and give rise to luminescence, which is the characteristic of the centres. When a II-VI semiconductor is fractured or cleaved initially the mechanoluminescence (ML) intensity increases with time attains a peak value I_m at the time t_m corresponding to completion of the fracture of semiconductors. After the completion of fracture, the ML intensity decay with time, whereby the initial fast decay is controlled by the pinning time of dislocations and the subsequent slow decay is controlled by the lifetime of electrons in the shallow traps. In the ML produced during the fracture of II-VI semiconductors, both I_m and I_T increase directly with the area of the newly created surfaces of the crystals. The ML intensity of II-VI compounds decreases with temperature. Expressions are derived for the rise of ML intensity, and the total ML intensity. A good agreement is found between the theoretical and experimental results related to the ML produced during the cleavage of II-VI semiconductors. Page(s): 421-428

Optical and dielectric properties of organic laser dye Rhodamine 6G doped silica xerogels with the variation of the sol-gel parameters

2010-06-02T16:31:27Z

Title: Optical and dielectric properties of organic laser dye Rhodamine 6G doped silica xerogels with the variation of the sol-gel parameters Authors: Rao, A Parvathy; Rao, A Venkateswara Abstract: The effect of sol-gel parameters such as pH of the alcosol, R6G/TEOS, H₂O/TEOS and EtOH/TEOS molar ratios on the optical and dielectric characteristics of R6G doped silica xerogels are reported here. Optical absorption and emission have been studied in the visible range. The dielectric property such as dielectric permittivity (') is carried out for pure and the R6G doped silica xerogels in the frequency range of the applied field (f) from 100 Hz to 1 MHz. It has been found that the optical and dielectric properties of the R6G doped silica xerogels are strongly dependent on the sol-gel parameters. Monolithicity and transparency of the R6G doped silica xerogels have also been studied. There is a remarkable shrinkage with the variation of the sol-gel parameters. Page(s): 413-420

Effect of tyre overload and inflation pressure on rolling loss (resistance) and fuel consumption of automobile and truck/bus tyres

2010-06-06T16:30:48Z

Title: Effect of tyre overload and inflation pressure on rolling loss (resistance) and fuel consumption of automobile and truck/bus tyres Authors: Pillai, Padmanabha S Abstract: The effect of rolling resistance R on fuel consumption of radial passenger and truck tires is discussed in this paper. The model equation for the rolling loss R was directly proportional to tire load W (R W) and inversely proportional to inflation pressure p (R 1/p^x). These relationships were experimentally quantified. Using manufacturer’s recommended values for load W and pressure p as reference points the R values for different overload conditions (from +10 to +100%) at constant p were estimated. Similarly, the required p values to support 10 to 50% additional load to maintain original R were also estimated. Then the estimated R values for different overload/inflation pressure conditions were combined with the fuel saving factor F (obtained from published literature results). Then the relative change in fuel consumption of truck/bus tires for different load/pressure combinations vis-a-vis the fuel use for the manufacturer’s recommended W and p values was evaluated. The present analysis showed that for the same amount of fuel use a truck carrying a 100% overload and making one round trip would correspond to slightly more than two round trips by a truck of same size carrying the recommended load. Finally, a possible method of optimizing fuel use by adjusting the tire load/pressure conditions was suggested. All these estimates were obtained for radial tires. The author feels that the same methodology is applicable for bias tires also. Page(s): 406-412