JLA Vol:8 Iss:1 (Laser polarimeters: Overview of recent developments, design and applications)

Authors:
Vi´ctor Fajer Avila
Center for the Development of Scientific Equipment and Instruments, Ministry of Science Techonology and Environment, Havana, Cuba

Research carried out in Cuba has led to the design and construction of automatic polarimeters that use the He‐Ne laser as a luminous source and work on a magnetooptic principle of measurement. Physical and chemical investigations including the use of the He‐Ne laser as a light source are discussed. The principle of measurement for the design and construction of polarimeters, resulting in three different types of these instruments, is described. Finally, applications for magnetooptic polarimetry are described,...

JLA Vol:8 Iss:1 (Frequency–time characteristics of air‐borne signals from laser welds)

Authors:
D. Farson
K. Hillsley
J. Sames
R. Young

The acoustic emissions from laser lap welds in stainless steel sheet were recorded and analyzed. The acoustic signals emanating from the weld were sensed with an instrument microphone and analyzed using short‐time Fourier spectra to characterize their time‐frequency distributions. It was determined that the acoustic spectrum of good‐quality, full‐penetration welds could be differentiated from the spectra of poor‐quality welds, defined as either partial‐penetration welds or welds having a gap between the sheets being joined. A novel, relatively simple class...

JLA Vol:8 Iss:1 (Comparison of aluminum alloy welding characteristics with 1 kW CO and CO₂ lasers)

Authors:
Bu¨lent A. Mehmetli
Kunimitsu Takahashi
Shunichi Sato
Institute of Research and Innovation, Laser Laboratory 1201 Takada, Kashiwa‐shi, Chiba 277, Japan

Welding characteristics of various aluminum alloys (A1100, A2017, A5083, A6063, A7N01) are investigated with CW CO and CO₂ lasers near 1 kW power level. The beam characteristics of both lasers at the welding point are similar, so that a comparison can be made of the effect of the wavelength difference. The welding characteristics are assessed by measuring the size of the weld bead. It is found that the threshold power between heat‐conduction and deep‐penetration typ...

JLA Vol:8 Iss:1 (Recent progress in laser surface treatment: <emph type="4">I</emph>. Implications of laser wavelength)

Authors:
W. Bloehs
B. Gru¨nenwald
F. Dausinger
H. Hu¨gel
Institute fu¨r Strahlwerkzeuge, Universita¨t Stuttgart, Pfaffenwaldring 43, 70569 Stuttgart, Germany

The coupling mechanisms of laser radiation and the mechanisms of heat transport in the workpiece are considered. Starting from the well&hyphen;known basics of Fresnel absorption — valid only for smooth and clean surfaces — further effects of coupling are examined. Studies on the effects of surface modifications inherent to all industrial parts and process conditions are presented. The more appropriate term coupling rate is introduced: This describes the r...

JLA Vol:9 Iss:6 (&hellip; .But is it really safe?)

Authors:
Peter A. Smith
DERA Centre for Human Sciences, Farnborough, Hampshire, U.K.

JLA Vol:9 Iss:6 (Amendments to the Center for Devices and Radiological Health Federal Performance Standard for laser products)

Authors:
Jerome E. Dennis
Center for Devices and Radiological Health, Food and Drug Administration, Rockville, MD, U.S.A.

Federal law requires that all laser products that are imported into or introduced into commerce in the United States comply with the performance standard published in the Code of Federal Regulations (CRF), Title 21, Parts 1040.10 and 1040.11, administered by the Center for Devices and Radiological Health (CDRH), US Food and Drug Administration. Although it contains somewhat different requirements for hazard classification, engineering controls and labeling, the ANSI Z136.1 standard defers to the CDRH standard. The CDRH standard became effective in August, 1976 and ...

JLA Vol:9 Iss:6 (Evolving issues in laser safety)

Authors:
David H. Sliney
US Army Center for Health Promotion and Preventive Medicine, Laser/Optical Radiation Program, Aberdeen Proving Ground, MD 21010&hyphen;5422, U.S.A.

The approach to laser safety has come a long way since the 1960s when the first guidelines were issued by defense research organizations in the US and the UK, and then by the American Conference of Governmental Industrial Hygienists. Although the search for ‘eye&hyphen;safe’ numbers continues in a few laboratories, this work is almost exclusively centered on deriving retinal thresholds for ultra&hyphen;short (sub&hyphen;nanosecond) lasers. Setting limits in this temporal region has been difficult, since...

JLA Vol:9 Iss:6 (Intrapulpar temperature during continuous CO₂ laser irradiation in human molars: An <em>in vitro</em> study)

Authors:
Walter Niccoli&hyphen;Filho
Jose´ Camilo Furlani
Carlos Schwab
Fernando Vagner Raldi
Carlos de Paula Eduardo

To establish safety parameters, we in vitro studied the increase in intrapulpal temperature caused by the use of a cw CO₂ laser. A thermistor was implanted in the inner part of the pulpal chamber of 25 human lower third molars to measure the intrapulpal temperature produced by laser powers between 2–10 W and exposure times of 0.5–25.0 s. The Pearson linear correlation factor applied to the measured values showed there is a direct relationship between the independent variable and ...

JLA Vol:9 Iss:6 (Improved hole drilling using a high peak power Nd:YAG laser at the second harmonic wavelength)

Authors:
Xiangli Chen
Angel L. Ortiz
P. Randall Staver
William T. Lotshaw
Todd J. Rockstroh
Michael H. McLaughlin

We have previously described the drilling of advanced materials such as intermetallics, superalloys, and composites using an Nd:YAG laser operating at the fundamental wavelength of 1.064 μm [1]. We have now extended these studies to the second harmonic wavelength of 532 nm of a high peak power Nd:YAG laser. The results show that drilling using the shorter wavelength further reduces undesired thermal effects such as recast layers and heat affected zones. A comparison of these results with those obtained at...

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&hyphen;flow d.c.&hyphen;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&hyphen;in/ramp&hyphen;out rates. Many of these factors which occur in ...