• Refine Query
  • Source
  • Publication year
  • to
  • Language
  • 106
  • 11
  • 9
  • 5
  • 2
  • 2
  • 2
  • 2
  • 2
  • 2
  • 2
  • 2
  • Tagged with
  • 145
  • 145
  • 27
  • 27
  • 19
  • 18
  • 17
  • 14
  • 14
  • 13
  • 11
  • 10
  • 10
  • 10
  • 9
  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
11

Analysis of thermal effects produced by incident laser radiation on a structure /

DeBolt, Frederick C. January 1991 (has links)
Thesis (M.S.)--Rochester Institute of Technology, 1992. / Typescript. Includes bibliographical references.
12

Nonlinear UV laser build-up cavity an efficient design /

Rady, Nicholas Henry. Shiner, David C., January 2009 (has links)
Thesis (M.A.)--University of North Texas, May, 2009. / Title from title page display. Includes bibliographical references.
13

Laser beam interaction with materials for microscale applications

Nowakowski, Krzysztof A. January 2005 (has links)
Dissertation (Ph.D.)--Worcester Polytechnic Institute. / Keywords: laser beam characteristics; heat transfer; hole profile; MEMS; hole formation; laser micromachining; laser microdrilling; plasma effects; silicon; 304 stainless steel; Fourier theory; lattice-phonon vibration. Includes bibliographical references. (p.379-390)
14

Light-induced forces on small particles /

Ng, Jack Tsz Fai. January 2005 (has links)
Thesis (Ph.D.)--Hong Kong University of Science and Technology, 2005. / Includes bibliographical references (leaves 137-141). Also available in electronic version.
15

Molecular beam laser stark spectroscopy of highly vibrationally excited molecules

Stoer, Marcell 04 August 2017 (has links)
The Stark field perturbed spectra of near infrared vibrational overtones of hydrogen fluoride and acetylene have been measured with a high resolution molecular beam laser spectrometer. A high performance laser power build-up cavity (optical resonator) was constructed to measured the weak ro-vibrational transitions of the v₂ + 3v₃ vibrational combination band of acetylene. The measured gain of the build-up cavity was found to be at least 300 out of a potential 2000. The primary reason for the lower than expected gain was attributed to losses induced by the extreme heat build-up on the mirror surfaces. The electric dipole moment for the v = 3 vibrational overtone of hydrogen fluoride was determined to be 1.9614 ± 0.0021 Debye. This result was compared with predictions from the available theoretical models and some theoretical constants were revised based on the current contribution to dipole moment function of hydrogen fluoride. The Stark field perturbed spectra of the v₁ + 3v₃ and v₂ + 3v₃ vibrational combination bands of acetylene were analysed for their polarisability tensors. In order to complete the study, the ground electronic state static polarisability and anisotropy of the polarisability were also determined. They were found to be 3.96A³ and 1.071 ± 0.014A³, respectively. The |1030⁰0⁰> state (v₁ + 3v₃) was observed to be coupled with the |0040⁰0⁰> infrared forbidden state (4v₃) in the presence of the Stark electric field. The resultant analysis produced values of 4.62 ± 0.09A³ for the polarisability and 1.15 ± 0.03A³ for the polarisability anisotropy of the |1030⁰0⁰> state. The difference in energy between |1030⁰0⁰> and |0040⁰0⁰> was determined to be 4.133 cm⁻¹, which compares well with local mode calculations. The measurements of the v₂ + 3v₃ band indicated that the |0130⁰0⁰> state was strongly coupled with another infrared allowed, unidentified (rogue), state in the absence of the Stark field as well as with the infrared forbidden, |1120⁰0⁰> state in the presence of the Stark field. The previously unobserved J = 5 ← 4 transition of the infrared allowed rogue state was recorded here for the first time. The Stark field perturbed spectra of the R(3) and R(5) ro-vibrational transitions of the v₂ + 3v₃ band also showed evidence of rogue transitions. The ensuing analysis determined that the |0130°0°) state has a polarisability of 3.5 ± 0.3A³ and a polarisability anisotropy of 5.6 ± 1.8A³. The Stark field perturbed spectra of the R(3) and R(5) transitions were fit to a non-crossing model and the energy levels of the rogue J = 4 and J = 6 states were determined. The energy level difference between |0130°0°) and |1120°0°) was determined to be -11.88±0.22 cm⁻¹. This does not compare well with local mode calculations and it is possible that the perturbations due to the presence of the rogue state impeded the accurate determination of the energy level difference. The identity of the rogue vibrational state could not be determined from the data presented in this thesis alone. However, collaborative work with another research group suggests that the rogue vibrational state is |0306°3¹) (see Chapter 7). / Graduate
16

Investigation of tellurium for the detection of pulsed CO2 laser radiation

Ribakovs, Gennadijs January 1976 (has links)
No description available.
17

In situ laser activation and renewal of solid electrodes /

Poon, Melanie J. January 1987 (has links)
No description available.
18

The effect of turbulence on laser beam quality /

Rivir, Richard Byram January 1976 (has links)
No description available.
19

Optical wave propagation through non-Kolmogorov atmospheric turbulence

Liptack, Paul Anthony 01 January 2004 (has links) (PDF)
The effect of atmospheric turbulence on an optical wave can seriously degrade the reliability of an optical communication link. One atmospheric effect is scintillation, which is caused by index of refraction fluctuations. Several observations of atmospheric turbulence statistics suggest a modest change in the power law behavior of Kolmogorov' s power spectral density model. The corresponding index of refraction fluctuations are assumed to have spatial power spectra that obey power laws that deviate somewhat from the classical - 11/3 power law. The purpose of this study is to develop analytical models for scintillation and other wave propagation statistics based on non-classical power spectra. This involves random processes, asymptotic theory, and evaluating integrals involving special functions (Bessel functions and hypergeometric functions). Mean irradiance and scintillation index models are derived for a Gaussian-beam wave propagating through an atmosphere experiencing weak irradiance fluctuations. Also, the wave structure function for an unbounded plane wave and spherical wave is derived under weak turbulence theory. Using the derived plane wave structure function, the scintillation index for both a plane and spherical wave experiencing strong irradiance fluctuations is calculated. In addition, a scintillation model that is valid under all irradiance fluctuation conditions is derived for both a plane and spherical wave propagating through non-Kolmogorov atmospheric turbulence.
20

On the interaction of laser beams with air : with specific reference to refraction and scattering.

Kuppen, M. January 1996 (has links)
The interaction of laser light with a parcel of air with a known density structure can result in one of three reactions. The simplest of these reactions is reflection. Depending on the nature of the density profile, that part of the light that is not reflected can be refracted or scattered. The extent of the refraction and scattering is determined by the density of the particles found in the air. This thesis investigates two concepts that use the above mentioned interactions. The first, the colliding shock lens (CSL) was proposed by Buccellato, Lisi and Michaelis (1993). This device uses the graded index (GRIN) lens formed by the collision of symmetrically arranged shock waves to focus a laser beam. Unfortunately, the first reported colliding shock lenses had optical apertures of the order of millimeters. This is hardly useful in realistic laser systems whose beams typically have a diameter of 10mm. The major part of this thesis involves the scaling up of the optical aperture of the CSL while simultaneously maintaining a fairly short focal length. We show how the behaviour of the CSL varies with factors such as input energy, electrical diameter, geometry and various other factors. By optimising the physical parameters a 1.5cm diameter lens is obtained having a focal length of 1.5m. We develop a simple scaling theory and run a simulation based on the fluid in cell (FLIC) method, and find good correlation in both cases between the experimentally obtained results and the theoretically predicted ones. As a further development of the work on colliding shock lenses we introduce a cylindrical colliding shock lens. This device is shown to be able to line focus a laser beam of 1cm in diameter. At this stage the focus quality is still poor and suggestions are made for further improvements. Lidar is an acronym for light detection and ranging. Such systems are based on the scattering of laser light incident on a parcel of air. We discuss the results of a campaign conducted during the period of June to November 1994 to study aerosol concentrations over Durban. Particular attention is paid to low level aerosols due to sugar cane burning over the Natal coast. These aerosols are known to influence local climate and since vertical profile studies have never been carried out, this investigation gives some useful insight into the atmospheric dynamics. We find that in June (the begining of the burning campaign) the aerosol loading in the lower atmosphere is low. However, there are very stable aerosol layers at 3km and 5km. The density of the aerosols in these layers are decoupled. In September, the turbulent atmosphere over Durban is found to destroy structure in the aerosol layers. Nevertheless, the aerosol loading is high. Scattering ratios and extinction coefficients are calculated to show the long and short term evolution of the aerosols. A new coefficient (the low altitude aerosol coefficent - LAAC) is defined as an indicator for aerosol loading in the lower atmosphere. This coefficient is compared with total column ozone values over Durban. An anti-correlatory behaviour is noticed. We also report the detection of an extremely high aerosol layer (60km) over Durban. This layer is believed to be sodium. The profiles are compared to satellite data to verify the first ever detection of a constituent at these altitudes in Southern Africa. / Thesis (Ph.D.)-University of Natal, 1996.

Page generated in 0.0418 seconds