• 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 ...

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  • JLA Vol:9 Iss:6 (Effect of nozzle orientation on the gas dynamics of inert-gas laser cutting of mild steel)


    Authors:
    Aaron D. Brandt
    Gary S. Settles
    Gas Dynamics Laboratory, Mechanical Engineering Department, Penn State University, University Park, PA 16802, U.S.A.


    This investigation applies sonic and supersonic coaxial and off‐axis nozzles to the cutting of mild steel sheet of 1–4 mm thickness. A 1.5 kW CW CO2 laser is used with nitrogen as the assist gas. Sonic coaxial cutting is compared to that of off‐axis nozzles, which vary in orientation from 20–60° behind the laser axis and in exit Mach number from 1 to 2.4. Results show a 50% increase in maximum cutting speed at approximately a 40° off‐axis nozzle angle. In com...

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  • 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 21010‐5422, 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‐safe’ numbers continues in a few laboratories, this work is almost exclusively centered on deriving retinal thresholds for ultra‐short (sub‐nanosecond) lasers. Setting limits in this temporal region has been difficult, since...

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  • 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...

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  • JLA Vol:9 Iss:6 (Intrapulpar temperature during continuous CO<sub>2</sub> 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 ...

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  • JLA Vol:9 Iss:6 (Scaling laws for thick&hyphen;section cutting with a chemical oxygen&ndash;iodine laser)


    Authors:
    A. Kar
    J. A. Rothenflue
    W. P. Latham



    Almost all laser&hyphen;assisted materials processing involves melting, vaporization and plasma formation which affect the utilization of laser energy for materials processing. To account for the effect of these phases, an effective absorptivity is defined, and a simple mathematical model is developed for the cutting of thick&hyphen;section stainless steel using a high power chemical oxygen—iodine laser (COIL). The model is based on an overall energy balance, and it relates the cutting depth with various process parameters that can be used to predictively scale the laser materials processing performance to ...

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