Browsing by Subject "Laser beams"

Now showing 1 - 7 of 7

Experimental studies in laser interaction with wavelength scale matter via second harmonic production and hard x-ray production
(2006) Sumeruk, Hernan Ariel; Ditmire, Todd R.
This dissertation presents the results of two experimental campaigns in the field of high intensity laser matter interaction. A common thread with both experiments was the use of wavelength scale spheres as the targets. A crucial feature of our experiments was the use uniformly sized spheres; this was done in order to facilitate exploration and interpretation of light interaction at this size scale. The first experiment was an attempt to measure the angular distribution of the second harmonic radiation from wavelength sized spheres. We run many versions of this experiment incrementally refining our technique but at the end the desired signal was too weak to be reliably reproduced. The second experiment measured and characterized an increase in x-ray yield of a target coated with wavelength scale spheres. We conducted the experiment with a range of sphere sizes and we noted a peak in the x-ray yield at a sphere diameter of 0.26 micrometers corresponding to a size parameter of 2.04.
Frequency Domain Holography of laser wakefields
(2006) Matlis, Nicholas Hill; Downer, Michael Coffin
In this dissertation, single-shot measurement of longitudinal and transverse structure of resonantly driven laser wakefields by Frequency Domain Holography (FDH) is demonstrated. Visualization of laser wakefield structure is crucial for understanding the complex dynamics of the mutual interaction between the driving pulse, wake- field density oscillations and accelerated electron bunch. This diagnostic therefor provides a necessary tool for researchers to learn how to control and fine tune the interaction to produce electron beams with desirable properties. Wakefields were measured in a 2 mm Helium gas jet, for electron densities between 1 x 1018 and 6 x 1018 cm−3 , and laser pulses of 30 fs duration and peak powers between 10 TW and 30 TW. Detailed structural features of the wakefields, including radial extent of the wake, longitudinal wake development, and wavefront curvature, as well as features of the accompanying ionization front and plasma column are resolved. Results are compared with PIC simulations, and show a high degree of correspondence. Weaknesses of the current implementation of the technique and extensions to other parameter regimes are discussed.
Interaction of intense laser fields with carbon nanotubes
(2006) Hsu, Han; Reichl, L. E.
The main topic addressed in this dissertation is the interaction of intense laser fields with the π electrons of single-walled carbon nanotubes. Since it is very difficult to carry out ab initio calculations for nanotubes in the presence of intense laser fields, we first propose a simple but realistic model to simulate the π electrons in a graphene layer and single-walled carbon nanotubes. We replace the atomic potential of each carbon atom of graphene or nanotubes by a two-dimensional attractive regularized δ function. By adjusting the parameters in this simple δ-potential model, we successfully reproduce the band structures and wave functions for graphene and nanotubes calculated by ab initio methods. With its simplicity and accuracy, we can use δ-potential model to study the interaction of intense laser fields with nanotubes. Combining the δ-potential model and Floquet-Bloch theory, we calculate the electronic states and the electron motion in an armchair nanotube driven by monochromatic intense laser fields with polarization parallel to the nanotube axis. The intensity and frequency (photon energy) of the applied laser fields are varied so their effect on the electrons can be understood. In each case, Floquet-Bloch theory is used to calculate the Floquet-Bloch states, quasienergy band, mean energy band, and electron current density. By summing up the current density of all occupied Floquet-Bloch states, the harmonic generation spectrum can be determined. We demonstrate that the deformation of quasienergy band and mean energy band is related to high-order harmonic generation. Only the states deviating from field-free eigenstates may contribute to high-order harmonic generation.
Laser chemical vapor deposition of millimeter scale three-dimensional shapes
(2001-08) Shaarawi, Mohammed Saad, 1973-; Sanchez, J. M. (Juan M.)
Laser micro/nano scale processing of glass and silicon
(2006-05) Theppakuttai Komaraswamy, Senthil Prakash, 1977-; Chen, Shaochen
The revolutionary progress in semiconductor, communication, and information industries based on electronic and photonic technologies demands for the development and enhancement of new laser processes to support micro and nanotechnologies. This dissertation is aimed at exploring the use of lasers for micro and nano scale processing of glass and silicon, the most commonly used materials in the IC industry. The objective of the dissertation is two fold: a) use lasers for locally micro bonding glass and silicon wafers, and b) use lasers for nanopatterning glass and silicon substrates by circumventing the diffraction limit of light. In the first part of the thesis, glass and silicon wafers are bonded locally in microscale by a pulsed Nd:YAG laser. Glass is transparent to the wavelength used and hence the laser beam passes through the glass wafer and is absorbed by silicon. As a result, silicon is melted and upon resolidification bonding is realized between the two substrates. The transient melting and resolidification of the substrates is studied experimentally and compared to the simulation results of a finite element numerical model. The bonded areas are studied in detail using a scanning electron microscope and a chemical analysis is done to understand the bonding mechanism. In the second part of the thesis, nanopatterns are created on glass and silicon substrates by circumventing the diffraction limit of light. The nanofeatures are created by irradiating silica and gold nanospheres deposited on a substrate. In case of silica spheres, features approximately half the diameter of the sphere were obtained by utilizing the optical field enhancement around the spheres. In case of gold spheres, features as small as 40 nm were realized by the excitation of coherent resonant electron plasma oscillations. The effect of sphere size, laser wavelength, polarization, incident angle, and energy were studied experimentally. Finally, these experimental results are compared with the numerical results from a multidimensional, heat transfer model.
Laser wakefield acceleration
(1995-05) Fisher, David Leonard; Not available
Laser-based solid freeform fabrication techniques for the direct production of ceramic and metal/ceramic shapes
(1995-08) Birmingham, Britton Ray; Not available