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JO D1 . cosO, cQnm = --l- 'lnar Emmple 8: Finding the Maximum Distance Where the Extended-Source MPE Applies. Find the maximum distance rr for a visible laser having an emergent beam diameter d = I cm, a beam divergence Q = l0' rad, and a pulse duration of 20 ps. A diffuse matte target is placed l@ cm from the beam exit of the laser; that is, th€ target distance r = 100 cm. The relation of D1 (in Fig. B I ) to the emergent beam divergence and diameter is: Dt=a+r'Q (Eq 84) At sholt target distances, where (r.Q) is nearly zero, Dz is clearly the same as a, or I cm, and using Eq 83 and finding o,n,n from Fig. 3, we have: Dlcos0u rlmu=c4oin which for small viewing angles, where cos0v = l, is a (l cm) (l) rr drw = - = -----j-:--:::r+j-.-_ = 625 cm oq.i^ (1.6x l0-r rad) Thereforc, for distances less than 625 cm, the applicable MPE from Table 6 or Fig. 7 is. MPE=l0rr/3J'cm-z.sar or MPE = 10(20x l0{)r'3 J 'cm-? . sal =2.'l2xll-t J .cm-2 . sal and for greater distances the applicable MPE from Tabte 5 or Fig. 4 is 5x l0-7 J' cm-2. This example illustrates that for most pulsed lasers the extended-source MPEs are applicable for diffuse reflections in such indoor areas as laboratories. Exceptions would be focused-beam diffuse reflections, such as those occuning in microdrilling processes, For visible cw lasers where the exposure time could b€ 0.25 s or greater and where a is often only 0,1 to 0.2cm, q;" is sufficiently great (10- 24 mrad) that the maximum distance r 1 at which the extended source MPEs apply would be only a few centimeters and the intrabeam MPEs would be more rclevant. For a = 0.1 cm, and o"nin = 24 mrad, rl mlx = a/ohin = 4.2 cm. Exatnple 9: Extended-Source MPEs for Diffuse Reflections Expressed as Incident-Beam Irradiance or Radiant Exposure. In most cases it is simpler to determine whether the incident-beam irradiance or radiant exposure is capable of producing a hazardous APPENDIX diffuse reflection, rather than having to deal with less familiar radiometric quantities such as radiance. Consider the laser defined in Example 8. Since the extended-source MPE is exprcssed as an integrated radiance, it is necessary to determine the beam radiant exposure at the target which Produces this integrated radiance. The relation is H.o\ L" = -------:-:: OI H = --------L Pr where L, is determined from Table 6. (F.q B5) Hence, the MPE expressed for a 100% - reflectance white diffuse talget is (3.14J Q.8x l?-t J . cm-2 . sr 1.0 = 0.88 J cm-' NOTE| Eq 85 is stricdy true only for a theoreticalty perfect Lambenian surface: however, unless a surface has a highly glossy !;heen, it may b€ considered sufficiently "diffuse" ro apply this formula and the diffuse-surface MPES. The above rcsult could have been obtained by interpolating the values in Column 4 of Table B I belween l0-" and l0* s. Example l0: Sp€ctral Corrections for Near Infrared Laser MPEs. A GaAs laser operating at room temperature has a peak wavelength at 0.904 pm. What is the MPE for a single pulse of 200 ns duration? The MPE can be calculated fmm the informalion in Table 5 and 6 or can be determined as follows: From Fig.8, note that the spectral corection factor C,{ is 2.5. From Fig.4, the MPE for direct viewing of the source is H = (2.5) (5x t0-7 J 'cm2; = l.28xl0{ J'cm-2 for a single pulse. Similarly, the extendedsource MPE (from Fig.7 for 200 ns) for sources subtending an angle greater ihan 3.3 mrad is (2.5) (5.8x l0 2 J .cm 2 sr-r;= 1.46 x 10-r J cm-z ' sal . NOTE: Unlike gas or solid-statc lasers, some semiconductor diqde lasers o. laser anays could be an extended source at close viewing range within the beam if the line source were magnified by a projection lens or a microscope-
APPENDIX B3.3 Central-Beam Irradiance or Radiant Exposur€. Often the beam inadiance or radiant exposure is not provided in a laser's specification. However, if the laser is single mode and has a Gaussian beam profile, the central-beam values may be obtained from lhe beam diameter specilied at l/e points and the beam radiant power or energy. The relations are - 40 1.274 (Eq 86) Lo= -.......--l = " 17a' 4- or . _" Q _1.?7Q ,to - -------; a - ------lta' a' Often the beam divergence or diameter is specified at lle2 points rather than aa the lle points, so that the above relations would provide average values rather than central-beam values. In such a case, divide the diameter specified at the l/e2 points by {7 to obtain the corresponding l/e value. Note however, that the MPEs can be specified as averaged either over a I mm or 7 mm aperture depending on the wavelength. In this case the calculated values of 11., or 8,, may not be relevant. 83.4 Laser Classification. Examples I I through 16 show nrethods ofcalculating parameters necessary for classifying lasers in accotdance with Section 3 of the standard. Example Il: Classify a single pulse (prt
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o SECTION 10. Revision of American
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SECTION Figures Fig. Bl Fig. 92 Fig
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American National Standard for the
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accessible radiation. Radiation to
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(See Appendix C for references.) If
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3.3.4 Ctass 4 Lasers and Laser Syst
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Page 61 and 62: o Appendixes Appendix A This Append
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APPENDIX simple heat flow models aP
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o APPENDIX Goldman, L., Rockwell, R
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Table l0 Control Measures for the F
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