Lasers can uniquely be used to create physical changes inside a bulk material. Traditional manufacturing
processes are limited to surface modifications, but a laser can be focused at any location inside a material transparent to
that wavelength. Using sub surface machining methods with ultrashort pulse lasers two practical applications are
demonstrated. First, a laser is used to sever short-circuited wires embedded deep inside a thick piece of glass, effectively
repairing a defective wire network. Second, subsurface bar-coding was shown to produce readable markings. Surface
laser markings were shown to weaken the glass, but subsurface marking had virtually no effect on strength.
Using a commercial laser system operating at a 532 nm wavelength with 10 ps pulses, experiments were conducted
on polished metal samples to study material removal characteristics from a low number of laser pulse exposures. The
samples were analyzed with a scanning electron microscope and white light interferometer to gather data on surface
deformation and material removal. The effects of energy and various double pulse machining methods were examined.
The results from changing the pulse separation for double pulse drilling are compared to prior work with picosecond and
nanosecond pulse lasers.
Using a picosecond laser system that can operate at 1064, 532, 355, and 266nm wavelengths, experiments were
conducted with polished metal samples to study material removal from a low number of laser pulse exposures. The
samples were analyzed with a scanning electron microscope and white light interferometer to gather data on surface
deformation and material removal. The effects of wavelength, energy and a double pulse exposure method were
examined. Results were compared with simulations that model the material removal rates from ultrashort pulse drilling.
The nanotechnology field is currently undergoing an exciting period of discoveries. It is necessary to bring nanotechnology to physics students. However, there is a lack of nanotechnology experiments developed for the undergraduate labs. By coupling high peak power laser pulses to a highly nonlinear photonic crystal fiber, supercontinuum generation and characterization are incorporated into nanotechnology education in undergraduate physics labs. Because of the fast advance and truly interdisciplinary nature of nanotechnology, the supercontinuum generation in photonic crystal fiber experiment gives physics undergraduate students an opportunity to work with high power lasers, to gain hands-on experience with state-of-art test and measurement equipment, and to access research projects in fiber optics, laser applications and nanotechnology.
Lasers are capable of delivering energy to a metal to induce stresses from the thermal gradient through the
material. Under the right conditions these stresses can cause the metal to bend. Experiments were conducted to produce
bending in the metal, Neyoro® G, and samples with a titanium coating on one side. In the experiments, both upward and
downward bending was observed. The titanium coated samples showed potential to be more controllable than the
uncoated samples.
Using a factorial design of experiments approach with ANOVA, laser drilling experiments were performed on the semiconductor mercury-cadmium-telluride (HgCdTe). A commercial CPA femtosecond laser system operating at 775nm was used for the experiments. The test variables include laser parameters such as pulse length, fluence, beam shaping using apertures, assist gas, vacuum, and others. The response variable examined for optimization include hole size, hole depth, and melt effects. The analysis yielded an empirical formula for predicting laser drilling effects.
The results of the interaction of the first harmonic of a 200 femtosecond laser pulse produced by a Ti:Sapphire commercial laser system and the third harmonic of a 40 ns laser pulse produced by a DPSS Nd:YVO4 laser with various materials are reported. The drilling rates were measured as a function of laser pulse energy and material thickness. Differences in material removal rates were observed between the low and high pulse energy. The dependence of the material removal rate on the sample thickness was measured. The observed dependencies of the drilling rate of a femtosecond laser on the laser pulse energy and material thickness are similar to a nanosecond laser drilling. This supports previously suggested hypothesis that a femtosecond laser system produces pulse containing a nanosecond pedestal with estimated energy comparable to the energy of the femtosecond component.
The results of a study of a single 200 femtosecond laser pulse interaction with thick stainless steel and HgCdTe samples are reported. The threshold pulse energies required to produce sample surface melting are measured. The melt dynamics, material removal rate and evolution of surface morphology were observed for different pulse energies and number of laser pulses. It was observed that, similarly to long laser pulse interaction, a layer of melt can be produced at the sample surface. Increase of laser pulse energy results in melt ejection in the radial direction toward the periphery of the interaction zone resembling evaporation recoil melt removal typical for laser interaction in range from nanosecond to cw. The removal of material from stainless steel sample was observed to be highly nonuniform. The columnar structures were observed on the surface of stainless steel samples. The period of these structures is dependent on laser pulse energy and number of pulses. The observed melting threshold is compared with the theoretical prediction obtained using two-temperature model.
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