JLA Vol:9 Iss:3 (Laser through‐cutting and drilling models for ablating/decomposing materials)

Authors:
Michael F. Modest
Department of Mechanical Engineering, The Pennsylvania State University, University Park, PA 16802, U.S.A.

A previously‐developed three‐dimensional conduction model for scribing of a thick solid has been extended to predict the transient temperature distribution inside a finite thickness slab that is irradiated by a moving laser source, and the cutting rate and profile carved by evaporation of material. The laser may operate in CW or in pulsed mode (with arbitrary temporal intensity distribution) and may have an arbitrary spatial intensity profile. The governing equations are solved using a finite‐difference method on a boundary‐f...

JLA Vol:9 Iss:3 (Diode laser scribing of non‐oriented 3 wt% Si‐steel for core loss reduction)

Authors:
Ravisankar Gurusamy
P. A. Molian
Mechanical Engineering Department, Iowa State University, Ames, IA 50011, U.S.A.

The electrical power industries are experiencing a considerable energy loss in transformers and motors because of inefficiencies caused by core loss. The objective of our research is to investigate any effect of laser scribing on the reduction of the core loss in the low cost, non‐oriented steels used in numerous utility applications. A 15 W diode laser transmitted through fiber optics was used to scribe 0.35 mm thick, non‐oriented 3 wt% Si steel. The magnetic properties including the core loss and permeability were evaluated both...

JLA Vol:9 Iss:3 (In‐process monitoring of laser welding by the analysis of ripples in the plasma emission)

Authors:
Kiyokazu Mori
Isamu Miyamoto

A novel in‐process monitoring system employing two detectors set above the workpiece at different aiming angles of 5° and 75° has been developed to detect whether or not CO₂ laser welding fully penetrates through to the back surface of steel sheets. The acquired signal contained a.c. components of the emission of the laser‐induced plasma in the plume and in the keyhole with frequencies up to approximately 10 kHz. The mean square value of the a.c. signal obtained by using the 75° sensor during full penetration welding was much larger than that of the partial penetration welding, showing that full p...

JLA Vol:9 Iss:3 (A power distribution model of industrial CO₂ lasers for system diagnosis)

Authors:
James G. Katter
Jay F. Tu
Mark Gartner

Industrial lasers are high power pieces of equipment that occasionally function under undesirable operating conditions. For example, the performance of a transverse‐flow d.c.‐excited gas laser can be adversely affected by many factors such as electrode arcing, poor lens and mirror cleanliness, focusing problems, improper gas mixture composition, poor gas quality, poor beam stability, poor beam path cleanliness, operator error, poor maintenance, poor chiller water temperature and flow rate stability, and improper laser beam ramp‐in/ramp‐out rates. Many of these factors which occur in ...

JLA Vol:9 Iss:3 (Effective laser ablation of enamel and dentine without thermal side effects)

Authors:
Peter Kohns
Ping Zhou
Reinhard Sto¨rmann
Optikzentrum NRW, Universita¨tsstraß 142, D‐44799 Bochum, Germany

We present a feasibility study into laser treating dental materials by using femtosecond pulses generated by a titanium:sapphire laser system which consisted of an oscillator and a regenerative amplifier. The pulse duration was varied between 200 fs and 2 ps. The observed energy thresholds for the ablation process of dentine and enamel were clearly smaller than those observed when longer pulse durations were used. The consequence of this observation is a lower thermal load within the vicinity of the radiated area. Thus no th...

JLA Vol:9 Iss:4 (Are we ready for the future?)

Authors:
R. James Rockwell
Rockwell Laser Industries, 77454 Camargo Rd., Cincinnati, OH 45243, U.S.A.

JLA Vol:9 Iss:4 (In the beginning there was ANSI Z136.1)

Authors:
Sidney S. Charschan
Charschan Associates, 7351 Kinghurst Drive, Delray Beach, Florida, U.S.A.

In the early 1960s concerns about eye safety were concentrated in a handful of research laboratories and the military. Memoranda and guidelines were circulated internally with their own set of priorities and recommended practices. Then, in 1968, the First International Laser Safety Conference (the brainchild of Dr Leon Goldman), was held in Cincinnati with one of its avowed purposes, the development of a consensus among the most prominent investigators as to what exposure criteria should be adopted. They saw the (laser) light. By 1969 it had become clear that, because of widespread d...

JLA Vol:9 Iss:4 (Dual wavelength laser beam alloying of aluminum alloy for enhanced corrosion resistance)

Authors:
Z. Liu
K. G. Watkins
W. M. Steen
R. Vilar
M. G. Ferreira

Aluminum alloys are known for their poor resistance to localized attack and, in particular, for pitting in chloride‐containing electrolytes. In this paper, improvement of the pitting corrosion resistance of 2014‐T6 aluminum alloy has been investigated by means of laser surface alloying of Cr into the substrate. Since aluminum is a highly reflective and thermally conductive material, it is often difficult to process with laser beams. Oxide films on the surface can prevent surface alloying as with the case of Cr alloying into aluminum by in‐situ...

JLA Vol:9 Iss:4 (The application of external feedback in the laser spectroscopy of nonlinear media)

Authors:
B. V. Anikeev
D. V. Sin'ko
Department of Laser Physics, Volgograd State University, 2‐aya Prodolnay 30, Volgograd 400 062, Russia

A new spectroscopic technique to gain information on the nonlinear constants of optical materials is presented. This technique is made possible due to the point that the application of an external controlled negative feedback (CNF) circuit to an intracavity nonlinear cell results in the generation of extended boundaries of the stability for the laser beam. This effect is analyzed using a semiclassical set of equations that govern laser oscillation. Measurements are made on systems containing either an instantaneous CNF circuit o...

JLA Vol:9 Iss:4 (The drilling of slate tiles by a Nd:YAG laser)

Authors:
F. Lusquin˜os
J. Pou
R. Soto
M. Pe´rez‐Amor
Departamento de Fisica Aplicada, Universidade de Vigo, Lagoas Marcosende 9, E‐36280 Vigo, Spain

We have undertaken a series of experiments to investigate the feasibility of using a Nd:YAG laser to drill slate tiles. Slate is used primarily as a roof building material after it is split into thin flat layers. The traditional fixation system of slate tiles in Europe consists of clamping the slate pieces by means of metallic clamps and overlapping the different tiles in order to form an impervious roof. An alternative to this clamping technique, is the use of nails to fix ...