JLA Vol:8 Iss:3 (Commonwealth of Independent States (CIS) laser scene and Laser Association (LAS) activities)

Authors:
Ivan B. Kovsh
LAS Headquarters, Moscow, Rozhdestvenkastr, 27, 117485, Russia

JLA Vol:8 Iss:3 (High‐power, high‐beam‐quality solid‐state lasers for materials processing applications)

Authors:
Lloyd A. Hackel
C. Brent Dane
Mark R. Hermann
John Honig
Luis E. Zapata
Mary A. Norton
Lawrence Livermore National Laboratory, P.O. Box 808, L‐487, Livermore, CA 94550, U.S.A.

The Laser Science and Technology Department at Lawrence Livermore National Laboratory is developing solid‐state lasers with high average power and high beam quality. Specific systems include a laser to generate 1.0–1.4 nm X‐rays for proximity print lithography, a 400‐mJ, 500‐Hz laser for 13.0 nm projection lithography and unique systems for speckle imaging, laser radars, and medical treatments.

JLA Vol:8 Iss:3 (Laser Hardened Materials Evaluation Laboratory (LHMEL))

Authors:
R. J. Hull
M. L. Lander

Since 1976, the Laser Hardened Materials Evaluation Laboratory (LHMEL) has been characterizing material responses to laser energy in support of national defense programs and the aerospace industry. Now that capability is available to commercial industry as well. LHMEL's power levels, beam uniformity, and diagnostics capabilities make it an ideal facility for proof‐of‐concept testing or process development. Located at Wright‐Patterson Air Force Base, Ohio, LHMEL is managed by the Wright Laboratory Materials Directorate and operated by Lawrence Associates, Incorporated. The facility's advanced hardware is centered aroun...

JLA Vol:8 Iss:3 (Laser shock processing of materials, physical processes involved and examples of applications)

Authors:
P. Peyre
R. Fabbro
L. Berthe
C. Dubouchet

Laser shock processing (LSP) consists of irradiating a metallic target with a short (about 20 ns) and intense (>10¹³W m⁻²) laser light in order to generate, through a high pressure surface plasma (>1 GPa), a plastic deformation and a surface strengthening within materials. This paper initially reviews the physical processes involved in the analytical modeling of the generation pressure mechanism in a confined plasma regime. Limiting factors such as the dielectric breakdown in the confining medium are also discussed together with current research directions aimed...

JLA Vol:8 Iss:3 (Parametric studies of cutting zircaloy‐2 sheets with a laser beam)

Authors:
Swati Ghosh
B. P. Badgujar
G. L. Goswami
Atomic Fuels Division, Bhabha Atomic Research Centre, Trombay, Bombay ‐ 400 085, India

The highly reactive and pyrophoric nature of zirconium alloys limits the use of conventional thermal sources (e.g., plasma arc cutting, oxygen flame cutting, etc.) for the cutting and drilling of these alloys. In this context, a highly coherent laser beam provides a good alternative for the cutting and drilling. In the present paper, laser beam cutting of zircaloy‐2 sheets of 1.1 mm and 0.74 mm thickness is performed using a 300 W average power pulsed Nd:YAG laser. Pulse energy, pulse repetition rate, nozzle ga...

JLA Vol:8 Iss:3 (Theoretical and experimental studies of thick‐section cutting with a chemical oxygen–iodine laser (COIL))

Authors:
A. Kar
J. E. Scott
W. P. Latham

A simple mathematical model of thick‐section stainless steel cutting with a high power chemical oxygen–iodine laser (COIL) is presented and compared with experimental results obtained with a 10‐kilowatt COIL at the U.S. Air Force's Phillips Laboratory. This model uses a lumped‐parameter technique to relate the cutting kerf depth with various process parameters and can be used to predict scaled laser materials processing performance to very thick sections. The model is similar to an empirical model developed by researchers in Japan, but includes predictive capabilities for thick metal cutting...

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 (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 (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 (On the relation between fluid dynamic pressure and the formation of pores in laser keyhole welding)

Authors:
John Dowden
Phiroze Kapadia
Andy Clucas
R. Ducharme
W. M. Steen

In the laser welding of metals with a continuous CO₂ laser, a hole containing a partially ionized metal vapor is formed throughout the depth of the material. A full description of flow conditions inside this hole is needed for a complete understanding of the process, but much can be learned from a simpler analysis of this aspect of the problem. The balance of forces that keeps the keyhole open can be investigated in this way. Such a model shows that over most of the keyhole's length, the dominant force keeping the keyhole open against surface tension...