COMPARATIVE ANALYSIS OF ACCELERATION GRADIENTS FOR CHIP STRUCTURES WITH DIFFERENT REFRACTIVE INDICES

The results of numerical studies of accelerating gradients in accelerators based on dielectric chip structures with different refractive indices, excited by a titanium-sapphire laser pulse, are presented. A comparative analysis of the influence of the refractive index on the rate of acceleration of electron bunches is carried out. Promising materials for the manufacture of dielectric laser accelerators are proposed.

Effect of Ti: Sapphire and Nd: YAG Lasers on Shear Bond Strength at the Zirconia - Veneering Ceramic Juncture

Introduction: This study was conducted to assess the impact of nanosecond and femtosecond lasers on shear bond strength at the zirconia - veneering ceramic juncture. Materials and Methods: The first 60 samples of partially sintered zirconia cylindrical discs measuring 7 mm diameter and 4 mm height were milled and sintered. Then they were randomly divided into three groups namely group C (control, n=10), group N (Nd: YAG laser, n=10), and group T (Ti: sapphire laser n=40) which was further divided based on the duration of laser irradiation, into 4 subgroups (n=10 each) which were 30 seconds, 1 minute, 2 minutes and 3 minutes. Surface treatment was done on sintered zirconia discs based on the group. Following the treatment, the discs were ultrasonically cleaned followed by liner application (IPS Emax Zirliner, Ivoclar-Vivadent) and veneer ceramic layering (IPS e.max Ceram, Ivoclar-Vivadent) of 1.5 mm height. Each sample underwent shear stress in the universal test machine on the mounting jig, and bond strength was evaluated. Data were assessed using ANOVA followed by Tukey’s post hoc multiple comparison analyses. Results: According to one-way ANOVA, there was a significant difference in shear bond strength between the groups. Tukey’s post hoc pair wise comparison test showed a significant difference (P value=0.001) in shear bond strength of all pairs except group C and group N. The results of repeated measures, ANOVA (related and dependent groups) and Tukey’s multiple pair wise comparison test showed that there was a significant difference (P value=0.001) in shear bond strength at 30 seconds and all other groups. Conclusion: Ti: sapphire laser irradiation for 30 seconds can be used as potential surface treatment to increase shear bond strength at the zirconia-veneering ceramic juncture.

A Study of Current Controlled Discharge in a Nitrogen Filled Tube

Time dependencies of the electrical resistance and electron density evolution in the discharge in a tube, with nitrogen at different pressures, with a diameter of 9.2mm and a length of 10cm were studied. A current pulse with an amplitude of 500A and duration of 10μs has created the discharge in the tube. Instantaneous electron densities are estimated from the interference pattern in Mach–Zehnder interferometer using femtosecond Ti: sapphire laser beam. Laboratory results are compared with results of computer modelling by MHD computer codes NPINCH and ZSTAR. Time development of the discharge resistance according to experiment is measured and evaluated. Minimum measurable value of the electron density in the experiment is determined as 2×1015cm−3.

Laser Lift-Off of the Sapphire Substrate for Fabricating Through-AlN-Via Wafer Bonded Absorption Layer Removed Thin Film Ultraviolet Flip Chip LED

In this study we report chip fabrication process that allows the laser lift-off of the sapphire substrate for the transfer of the GaN based thin film flip chip to the carrier wafer. The fabrication process includes 365-nm ultraviolet flip chip LED wafer align bonding with through-AlN-via wafer and sapphire laser lift-off. n-holes with the diameter of 100 µm were etched on the GaN epilayers for accessing n-type GaN. Through-AlN-via size was 110-µm and filled by Cu electroplating method for the electrical connection. Mechanical stabilization to prevent the GaN epilayers cracking and fragmentation during laser lift-off was achieved by utilizing epoxy based SU-8 photoresist support.