JLA Vol:7 Iss:1 (Taking advantage of laser properties to enhance demonstrations and student laboratories)

Authors:
Michele L. Brill
Camden County College—Physics/Lasers, Box 200, Blackwood, NJ 08012, U.S.A.

This paper reflects the proceedings of a workshop for local educators provided by Camden County College Laser Curriculum faculty which addressed the question: ‘How can the teacher take advantage of laser properties to improve or enhance demonstrations and student labs?’ Explored here are illustrative ways in which to utilize, for educational purposes, the three well‐known characteristics of lasers: monochromaticity, directionality, and coherence. There is a faculty overlap between the Physics Department and the Laser Curriculum faculty at the college. The use o...

JLA Vol:7 Iss:1 (Photodynamic therapy)

Authors:
Leonard I. Grossweiner
Physics Department, Illinois Institute of Technology, Chicago, IL 60616 and Wenske Laser Center, Ravenswood Hospital Medical Center, Chicago, IL 60664, U.S.A.

Photodynamic therapy (PDT) is a new treatment for solid tumors utilizing the combined action of light and a photosensitizing drug. Laser–fiber optic delivery systems make it practical to treat superficial and interstitial cancers, including malignancies of the skin, head and neck, esophagus, endobronchial tract, stomach, urinary bladder, female genital tract, and other sites. The putative action mechanism in PDT involves photochemical destruction of tumor tissue membranes mediated by singlet...

JLA Vol:7 Iss:1 (Laser chemical analysis of metallic elements in aluminum samples)

Authors:
B. Besco´s
A. Gonza´lez Uren˜a
Unidad de La´seres y Haces Moleculares, Instituto Pluridisciplinar, Universidad Complutense de Madrid, Juan XXIII‐1°, 28040‐Madrid, Spain

This paper reports on the simultaneous detection of Mg, Mn, and Ti in Al samples using laser‐breakdown spectroscopy and optical multichannel analysis of photoablated microplasma. Two different experimental procedures were used depending on the emission intensity selected as reference. For those elements like Mg and Mn having emission lines close to some line of the matrix element, a direct method was used that consisted of taki...

JLA Vol:7 Iss:1 (Ultrasonic vibration aided laser welding of Al alloys: improvement of laser welding‐quality)

Authors:
J. S. Kim
T. Watanabe
Y. Yoshida

Using a pulsed YAG laser, meltability of Al‐Mg and Al‐Mg‐Si alloys were investigated by a single‐pass irradiation. In order to improve the quality in laser welding, the effectiveness of the Ultrasonic Vibration Laser Welding (UVLW) method proposed in this paper was investigated experimentally. The proposed method was also compared with the traditional welding methods of Normal Laser Welding (NLW) and preHeating Laser Welding (HLW). The welding methods were evaluated from the geometry in the melt zone generated by a single pulse of the laser beam. It was suggested that ultrasonic vibration ...

JLA Vol:7 Iss:1 (Safe laser system design for production)

Authors:
Ami Kestenbaum
Richard J. Coyle
Patrick P. Solan
AT&T Bell Laboratories Engineering Research Center, Princeton, NJ 08542‐0900, U.S.A.

The majority of industrial lasers used in manufacturing are Class IV lasers. Engineering and administrative control measures appropriate to that class of lasers must be enforced to ensure their safe use in production environments, i.e. they should be designed into Class 1 laser systems. In addition, several other design characteristics unique to industrial applications are normally incorporated into these Class I systems, such as interlocked enclosures, process mon...

JLA Vol:7 Iss:1 (Development of laser finishing for non‐circular profiles)

Authors:
Ko‐Wang Liu
Paul S. Sheng
Department of Mechanical Engineering, University of California, Berkeley, CA 94720‐1740, U.S.A.

A laser‐based technique for finishing of non‐circular cylindrical parts is presented. In this process, the frequency characteristics of a desired non‐circular shape is extracted from a CAD through a Fast Fourier Transform algorithm and implemented through a CO₂ laser machining system. A galvanometer‐based scanner is used in the process to achieve programmable beam trajectories and high‐speed finishing. An error estimation scheme can be developed to determine the final dimensional erro...

JLA Vol:8 Iss:4 (Integrated instruction: Lasers across the curriculum in an associate's degree program)

Authors:
R. Allen Shotwell
Ivy Tech State College, 7999 U.S. Highway 41, Terre Haute, IN 47802, U.S.A.

JLA Vol:8 Iss:4 (Acoustic emission from modulated laser beam welding of materials)

Authors:
Hongping Gu
W. W. Duley
Guelph‐Waterloo Program for Graduate Work in Physics, University of Waterloo, Waterloo, Ontario, Canada N2L 3G1

Acoustic emission during the laser welding of metals with a modulated CO₂ laser beam has been investigated. Sharp resonances at many frequencies in the acoustic emission spectra have been observed. This was most noticeable when the average laser power was high enough to produce full penetration welds whose acoustic emission at high harmonics with frequencies that overlap with bands of vibrational frequencies corresponding to eigenmodes of the keyhole are greatly enhanced. Lower harmonics were not clearly observe...

JLA Vol:8 Iss:4 (Laser hazard evaluation method for middle infrared laser systems)

Authors:
Wesley J. Marshall
Robert C. Aldrich
Sheldon A. Zimmerman

Hazard evaluation methods for lasers, with wavelengths greater than 1.4 μm (mostly in the middle infrared), have changed significantly in the current version of the American National Standard for the Safe Use of Lasers, ANSI Z136.1‐1993. A correct evaluation involves comparing the hazard potential based on two evaluation models; one based on individual pulses and the other based on an equivalent continuous‐wave exposure. An example of the hazard evaluation method within this spectral region is provided.

JLA Vol:8 Iss:4 (Some aspects of laser heating of engineering materials)

Authors:
B. S. Yilbas
A. Z. Al‐Garni
Mechanical Eng. Dept., KFUPM, P.O. Box 1913, Dhahran, Saudi Arabia

Laser induced heating processes are important when a laser is used as a machine tool in industry, since the quality of the machining process strongly depends on the heating mechanism. The present study examines a heat transfer model that provides useful information on the laser induced interaction mechanism. Steady state and time dependent heating models are introduced and temperature profiles inside the materials are predicted. Using appropriate assumptions, the time for the surface temperature to reach 90% of its steady state value is estimated. To valid...