## 1 Introduction
[PERSON] and [PERSON] [8] utilized a near ultraviolet Nd:YAG laser for micromachining of sapphire and silicon. They found higher ablation efficiency when laser fluence increased slightly above the threshold values. However further increase in fluence did not show any improvement in ablation efficiency possibly due to laser attenuation. A short pulse Nd:YAG laser having wavelength of 355 nm and pulse duration of 15 ns was utilized by [PERSON] et al. [9] to generate microfeatures in diamond, silicon, and stainless steel. They showed that 1 mm thick silicon wafers can be machined easily without any microcracks but a small increase in pulse width resulted in thermal damage. For diamond, the third harmonic of an Nd:YAG laser was found to be suitable due to high absorption at this wavelength whereas steel was found to be less sensitive to the wavelength and microholes of good quality could be created at 1064, 532, and 355 nm wavelengths. [PERSON] et al. [10] produced microholes in Aluminum Gallium Nitride/Gallium Nitride transistors utilizing single crystal silicon carbide as substrate. They concluded that laser micromachining is a better choice in comparison to lithography and dry etching for these hard and chemically inert materials. Super hard nano polycrystalline diamond was machined by [PERSON] et al. [11] using three types of lasers: (a) nanosecond near-ultraviolet, (b) nanosecond near-infrared, (c) femtosecond near-infrared. It was found that rough surfaces were produced by ns laser with high average power. In contrast smooth surfaces were obtained using femtosecond laser with low average power. [PERSON] et al. [12] performed micro-drilling on alumina ceramic plate using a second and third harmonic Nd:YAG laser with a 6 ns pulse width. They showed that the plasma shielding mode is dominant at this wavelength and the increase of the diameter is more than the depth with the increase in average power. They also reported a decrease in crater diameter with increase of ambient pressure. A dual prism optical system with a UV Nd:YAG laser was utilized by [PERSON] et al. [13] to make different microfeatures on silicon wafers. They were able to develop microfeatures up to an aspect ratio of 10 that could be used for signal transducing elements in micro-electro-mechanical systems (MEMS). They reported that the efficiency of laser micromachining is not affected by the orientation of the silicon substrate. [PERSON] [14] examined trepanned drilling of through holes in borosilicate glass using fourth harmonic Nd:YAG laser. They reported an increase in the number of pulses and a decrease in the number of circular scans by increasing the number of lines per circular scans. Microhole drilling in metals, alloys, and ceramics using a picosecond laser was studied by [PERSON] et al. [15]. They utilized laser of wavelengths of 532 nm and 1064 nm with a percussion drilling technique and holes less than 50 \(\upmu\)m were produced in steel, silicon nitride and silicon carbide. They concluded that high quality microstructures can be produced in different materials by picosecond lasers. Microstructures in fused silica were examined by [PERSON] et al. [16] and they analyzed different mechanisms at very high laser fluence. According to them the ablation phenomenon is mainly dependent on feedrate while pulse energy mainly accounts for feature size. Analysis of microholes in alumina ceramic using a nanosecond laser was carried out by [PERSON] et al. [17] and they reported an improvement in the quality of microholes using laser repeat drilling in static water. [PERSON] et al. [18] studied the micro-groove development by nanosecond laser in green ZrO\({}_{2}\) ceramics. They investigated the effects of power, frequency, and scanning speed on morphology and the heat-affected zone around the machined textured grooves. They suggested power below 6 watts, frequency below 40 Hz, and scanning speed above 60 Hz for good surface quality. Femtosecond laser with helical drilling technique was utilized by [PERSON] et al.