JLA Vol:6 Iss:4 (Nd:YAG laser welding of coated sheet steel)

Authors:
M. P. Graham
D. M. Hirak
H. W. Kerr
D. C. Weckman
Department of Mechanical Engineering, University of Waterloo, Waterloo, Ontario, Canada, N2L 3G1.

The weldability of coated sheet steels by a 2 kW Nd:YAG laser has been examined. Laser seam welds were produced in 0.75‐mm thick (23 gauge) galvanized and galvannealed sheet steels in the lap‐joint configuration. Three types of laser beam power output were used: continuous wave, sine‐wave modulated, and square‐wave modulated. The effects on weld quality of varying laser welding parameters such as welding speed, shielding gas composition, and gas flow rate were stud...

JLA Vol:6 Iss:4 (Investigation into the underwater laser welding of steel)

Authors:
G. J. Shannon
J. Watson
W. F. Deans
Department of Engineering, Laser Laboratory, Kings College, University of Aberdeen, Aberdeen, U.K.

An investigation was undertaken using a 1.2 kW carbon dioxide laser for underwater butt welding of BS 4360 43A and 50D steel, in order to assess the quality of the welds and to achieve an understanding of the laser/water/material interaction. Using a high‐speed camera, the temporal behavior of the melt pool and “plasma” dynamics surrounded by an aqueous environment were monitored. Experiments were undertaken to characterize the attenuation of the laser beam in the water as a function of various foca...

JLA Vol:6 Iss:4 (Erratum: Excimer laser processing of Ti–6Al–4V)

Authors:
J. A. Folkes
K. Shibata
Nissan Motor Co. Ltd, Materials Research Laboratory, Central Engineering Laboratories, 1, Nasushima‐cho, Yokosuka 237, Japan

JLA Vol:6 Iss:4 (Characteristics of power meters for high power CO₂ lasers)

Authors:
Keng H. Leong
Donna J. Holdridge
Kenneth R. Sabo
Laser Applications Laboratory, Technology Development, Argonne National Laboratory, University of Chicago, IL 60439, U.S.A.

Four different instruments used for measuring CO₂ laser beam power in the kilowatt range were evaluated. The techniques used to determine the laser beam power included temperature increase from an absorber of known mass and specific heat, temperature increase from a steady flow of water used to cool the absorber, thermal gradient caused by edge‐cooling a circular absorber, and diffuse scattering from a small portion of the water‐cooled absorber surface. Th...

JLA Vol:6 Iss:4 (Effect of the helium–neon laser on the healing of extraction wounds: A histological study in rats)

Authors:
Walter Niccoli‐Filho
Tetuo Okamoto

A histological study on the healing of extraction wounds following laser irradiation using a He–Ne laser, was carried out in rats. The results suggest that this mode of treatment has a beneficial effect on initial bony wound healing. Proliferation of fibroblasts and formation of trabecular osteoid tissue were found to be more prominent within the irradiated group. The deposition of led in the newly formed bone suggests swifter ossification within the irradiated group.

JLA Vol:6 Iss:4 (Exposure to “lessons learned”: A tool for laser safety)

Authors:
Kenneth Barat
Susan Elisabeth Kelly
Lawrence Berkeley Laboratory, Environment, Health & Safety Division, University of California, Berkeley, CA 94720, U.S.A.

This article outlines the value and steps to follow for establishing a “lessons learned program”, with specific application to a laser safety program. As a communication tool and preventive measure for laser safety issues, the program is an effective means of turning accident investigation into a proactive rather than a reactive exercise by emphasizing corrective rather than disciplinary (looking for someone to blame) actions.

JLA Vol:6 Iss:4 (Holographic optical elements (HOEs): A serious application of holography)

Authors:
Gareth T. Williams
Jeff Fredrick
Physics Department, San Jose State University, San Jose, CA, U.S.A.

Without disputing the excitement and sense of accomplishment associated with the production of display holograms, this paper suggests equal rewards from the production of holographic optical elements (HOEs). The elements described here are zone plates, diffraction gratings, interference filters and mirrors, and lenses. Ways of making each of these in an optics teaching laboratory are described, but the main emphasis will be on positive lens HOE.

JLA Vol:6 Iss:4 (Effective laser applications in high school physics)

Authors:
Jeff Sweet
North Salinas High School Salinas, CA 93906, U.S.A.

Laser light is an instant attention‐getter in the classroom; thus any activity which uses the laser as an instructional tool is sure to enhance student motivation. This paper discusses two demonstrations and one experiment involving laser applications that the author has found to be particularly beneficial in terms of (1) instructional effectiveness and (2) arousing the interest of high school physics students. Brief descriptions follow. Refraction through lenses can be nicely illustrated by splitting laser light into several parallel beams and directing them through a fish tank filled with a scatt...

JLA Vol:6 Iss:4 (Inexpensive photodetectors for the classroom)

Authors:
Lewis R. Smith
Science Department, Leigh High School, San Jose, CA, U.S.A.

Many simple concepts that we introduce in optics could lead to laboratory work if we had access to photodetectors that could give a quick voltage or current response proportional to the light intensity. The device described here is easily constructed from readily available parts at a cost of about $2.00 and can be used with any light source and any conventional voltmeter.

JLA Vol:5 Iss:2 (Real‐Time Fast Fourier Transform Analysis of Acoustic Emission during CO₂ Laser Welding of Materials)

Authors:
Y‐L. Mao
G. Kinsman
W. W. Duley
Physics Department, University of Waterloo, Waterloo, Ontario, Canada, N2L 3G1

Real‐time fast Fourier transform (FFT) analysis of acoustic emission has been developed for monitoring laser welding processes. Significant differences in acoustic emission have been observed in conduction and keyhole processing regimes. The amplitude fluctuation of acoustic emission becomes intensified in the transition from conduction welding to keyhole welding. The integrated FFT power spectrum emission has been correlated to laser power, welding speed, and focusing parameters. These results suggest a simple way of monitori...