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Nanosecond laser Bessel beam scribing on the TCO thin film was investigated to improve processing precision and robustness of optical system. Fundamental wave (1064 nm) of Nd:YAG laser was shaped into high-quality Bessel beam by using novel optical system consisting of axicons and convex lens. Spatial FWHM of the beam was only 1.5 μm in the present context, and significantly precise scribing with minimum width of 2.3 μm was achieved on 600–700 nm-thick FTO film with electrical isolation. Furthermore, due to the critically deep focal length of millimeters-order, robustness on sample positioning was greatly improved. Additionally, experimental results showed that single shot removal of entire film can be achieved using film side irradiation unlike conventional Gaussian beam. Temperature distribution during the process was calculated by a numerical model in which we have taken into account beam propagation inside the film to give comparison with a Gaussian beam irradiation. The calculation results showed that only Bessel beam is self-reconstructed behind plasma shielding so that entire film can be removed by single shot. Our findings suggest that Bessel beam can be used for efficient IR scribing with significantly high quality without selecting substrate material.

Role of optical parameters on nanosecond laser drilling of 4H-SiC was experimentally studied. Using ns pulsed Nd:YAG laser, parametric studies on effects of wavelength (1064 nm or 532 nm), beam profile (Gaussian or Bessel), and ambient condition (air or water) were conducted. The wavelengths which have large optical penetration depth were selected as wavefront has to propagate through materials to generate Bessel beam. The experimental results showed that carbonization of SiC surface accelerates thermal ablation of the materials with fluence under the lattice melting threshold. Especially, pattern of side lobes with small fluence was formed by irradiation of Bessel beam. The pattern disturbed penetration of wavefronts through materials. Implementation of water environment was not effective to suppress carbonization and had slight effect on improvement of drilling quality. For this reason, deep drilling with small entrance was not achieved using Bessel beam. Irradiation of 1064 nm Gaussian beam with large fluence led to formation of critical amount of re-solidified silicon due to the large optical penetration depth. Carbonization and silicon formation had a significant effect on unique fluence dependence of drilling depth. Absorption mechanism was studied as well to discuss effect of wavelength on processing characteristics.

Laser drilling of silicon carbide (SiC) wafer in air (dry ablation) and underwater by using ns pulsed infrared (1064 nm) Nd:YAG laser is investigated. In order to suggest optimal parameters of via processing in SiC wafer, the effects of pulse number, laser fluence, water film thickness, and focus position are evaluated. As compared with dry ablation vias, decreasing etching rate, increasing via diameter, and generation of cracks in high-energy regime are observed in liquid-assisted processing. However, it is found that it can create vias without debris, HAZ, cracks. Also, optimal parameter set for infrared pulse laser processing under water is found to be the laser fluence of less than 10 J/cm2 and water thickness of 1 mm.

This work presents a fundamental study about ablation threshold, absorption coefficient and absorption mechanism of silicon carbide (SiC) in the laser drilling process. Experimental study has been performed on single infrared (1064 nm) ns pulse laser ablation of SiC at various fluence values. Hole diameters were measured to predict the absorption threshold. Based on the ablation threshold, an average absorption coefficient of SiC at infrared wavelength during the laser ablation process is calculated. The result is discussed based on absorption coefficient dependence on doping concentration and temperature in semiconductor. A preliminary model is proposed that accounts for the heat conduction and surface evaporation to predict the cross-sectional shape of drilling hole. Analytical modeling results are in good agreement with observed features produced from the laser. The paper will conclude with suggestions for further research and potential applications for the work.

Laser beam shaping techniques are important to optimize a large number of laser-material processing applications and laser-material interaction studies. The authors have developed a novel fluidic laser beam shaper (FLBS) with merits such as flexiblility, versatility and low cost. This work presents a fundamentally new approach for laser beam shaping by using FLBS. A Gaussian beam profile is transformed to a flat top beam and annular beam profile in the focal plane. The shaped laser beam is used for laser drilling to investigate the influence of the laser intensity profile in laser processing. The paper concludes with suggestions for future research and potential applications for further the work.Copyright © 2013 by ASME

Laser measurement and laser processing techniques have been gaining strong attention from various applications. This research aims at the development of a novel optical device, and in order to fulfill the objective, characteristics of the thermal lens effect is studied. This phenomenon has the optical property of a divergent lens since the refractive index distribution on the optical axis is formed when the liquid medium is irradiated. One reason for the refractive index distribution is the temperature distribution in the liquid medium when it is irradiated. In this research, as a fundamental step to develop the fluidic optical devices, the interaction between a refractive angle of the probe beam and the temperature distribution on the thermal lens effect is investigated.

A numerical model of the thermoreflectance of doped SiC substrate and typical numerical results are presented. The model considers the temporal response of the electron temperature and the number density of the electronic carriers. Calculated results show steep increase of electron temperature and the resulting increase of reflectivity. As a result, the reflected laser pulse by the substrate is compressed in time domain by means of the temporal response of the thermoreflectance characteristics of SiC substrate. Thermal analysis of the electrons reveals the interesting feature of the thermoreflectance response as a function of pulse intensity, pulse width, or doping concentration. The technique can be used for the compression of ultrashort pulse laser light.Copyright © 2013 by ASME

Laser drilling of silicon carbide (SiC) wafer in air (dry ablation) and underwater by using ns pulsed infrared (1064 nm) Nd: YAG laser is investigated. In order to suggest optimal parameters of via processing in SiC wafer, the effects of pulse number, laser fluence, water film thickness, and focus position are evaluated. As compared with dry ablation vias, decreasing etching rate, increasing via diameter, and generation of cracks in high-energy regime are observed in liquid-assisted processing. However, it is found that it can create vias without debris, HAZ, cracks. Also, optimal parameter set for infrared pulse laser processing under water is found to be the laser fluence of less than 10 J/cm2 and water thickness of 1mm.

Laser measurement and laser processing techniques have been gaining strong attention from various applications [1,2]. This research aims at the development of a fluidic laser beam shaper, and in order to fulfill the objective, characteristics of the thermal lens effect are studied. This phenomenon has the optical property of a concave lens since the refractive index distribution on the optical axis is formed when the liquid is irradiated. One reason for the refractive index distribution in the liquid is the temperature distribution in the liquid when it is irradiated. In this research, effects of the pump power and propagation distance of the probe beam to probe beam profile are investigated experimentally and theoretically, in order to develop fluidic laser beam shaper. It is indicated that, by controlling some parameters in thermal lens system as pump power (in the regime of linear optics) and absorption coefficient, input Gaussian beam can be converted into flat-top beam profile. The relationship among the distance to obtain a flat-top beam, pump power and absorption coefficient is investigated to show the flexibility of fluidic laser beam shaper in many fields of laser application.

Recent advances in measurement techniques using the photothermal effect have drawn more and more attention to the application in various fields. Especially, laser measurements are becoming increasingly important for the thermal design of electronic devices because these measurements can be applied to non-invasive and non-destructive measurement [1, 2]. We focus on the transient lens effect, which is a well-known photo-thermal phenomenon. As this effect is caused by the change of thermal properties or other physical properties, the measurements using this effect have the possibility to measure various materials information. This phenomenon has the optical property of a concave lens since the refractive index distribution on the optical axis is formed when the liquid is irradiated. One reason for the refractive index distribution in the liquid is the temperature distribution in the liquid when it is irradiated. In this research we investigate the interaction between refractive index and temperature distribution on the Transient lens effect, in order to develop fluidic optical devices