A study on the preparation of thermally stable phosphor targets based on yttrium aluminium garnet doped with cerium (YAG:Ce) when excited by a high power laser diode is described. The luminous flux, chromaticity and Radial spectral flux of the targets along with their thermal stability have been determined when exposed to laser powers of up to 5000mW. This report presents successful high brightness light sources with adjustable emission properties achieved by utilising thermally stable phosphor targets excited by high power laser diodes.

The photometric properties of an radio frequency (RF)-based sputtering plasma source were monitored through optical spectroscopy. The colour of the plasma source was deduced based on conventional chromaticity index analysis and it was compared to the direct spectral data plots of the emission peaks to investigate the possibility of characterising the plasma based on its specific colour and exploring the potential of defining a new method by which the plasma sputtering process can be addressed based on the plasma colour parameters. The intention of this investigation is to evaluate the possibility of simplifying the monitoring and assessment of the sputtering process for applied scientists operating plasma sputter deposition systems. We demonstrate a viable potential for this technique in terms of providing information regarding the stability of the plasma, chamber pressure, and plasma power; however, further work is underway to verify and assess a relationship between the quality of the thin film coating and the colour characteristics of the deposition plasma. Here, we only focus on the feasibility of such an approach and demonstrate interesting observations. We observed a linear relationship between the colour functions and the plasma power, while the stability of the sputtering plasma can be assessed based on the plasma colour functions. The colour functions also follow a unique pattern when the working gas pressure is increased.

Limitations associated with light emitting diodes (LEDs) operating under high current densities due to the efficiency droop has created a need to look for alternative light sources; here we report investigations on the potential of laser diodes (LDs) for high brightness lighting solutions. High power laser diodes require phosphor targets with certain performance criteria such as high thermal conductivity, efficiency and structural geometry. Here we examine the possibility of using single crystal YAG:Ce phosphor materials as potential targets for generation of light via laser diodes. We report on the emission properties of the crystals with different sizes and examine the effect of laser beam incident angle incident on crystal target emission. Light emitting diodes (LEDs) are the current lighting technology solution gaining a wide adoption in a variety of commercial applications. They are now the dominant new lighting in office, public and domestic application, in addition they have almost completely covered the automotive head lamp market and now they are finding their way into more sophisticated instruments such as solar simulators. The best commercial LED's efficiencies are now above 60% and they are the most energy saving solution available. However there is a fundamental issue undermining their performance when they are considered for high brightness lighting applications. To generate high emission intensities, LEDs need to be driven at high current densities at which point their efficiency suffers from a phenomenon described as the efficiency droop. The efficiency droop's origin is rooted in a variety of complex processes including; Auger recombination, overflow of carriers from rich potential minima and carrier leakage out of active region.1-8 So far the highest luminous efficacies reported on LEDs are based on driving them at low current densities on the order of >11 Acm −2 . 9,10 In contrast to LEDs, Laser Diodes (LDs) can operate at very high current densities without suffering from efficiency droop. 11,12 However currently the LD's overall efficiency is well below that of LEDs and their application in lighting will require radical packaging designs and arrangement of the laser diode and phosphor target assemblies. To be able to manipulate the emission spectrum of devices based on LD induced lighting (LDIL) the type of phosphor targets and the level of impurities constituting the phosphor target material will need to be studied and adjusted. Recent research has demonstrated the necessity of these studies by investigating the structural and thermal properties of Tb, Ce doped Y 3 Al 5 O 12 (YAG) single crystals. 13,14 The results act as pointers to the research that needs to be undertaken in parallel to both develop radical designs of LDIL modules and the associated single crystals used as emitting targets. In this report we have focused on studying different crystal sizes of the same phosphor material with the same LDs. We have carried out studies on beam incident angle and relationship between the emiss...

Abstract-In this paper we have applied a new anisotropic zero index metamaterial (ZIM) structure to the quasi-Yagi antenna to achieve a high-directivity quasi-Yagi antenna. Simulation results show the antenna gain increases over the bandwidth of anisotropic ZIM (10.3-11.7 GHz).