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RE: Laser calculations
All visible laser's that produce 1 - 5 mW output power are class 3a. This
includes almost all laser pointers. Although technically they are capable of
producing eye damage there has been only one documented case to date. This
occurred when 2 young girls had a dare as to who could stare into the laser
the longest. Your calculations appear correct. The only real way to get eye
damage from a laser such as this is with intentional viewing. Although the
MPE would be exceeded in less than 0.25 seconds several safety factors are
built into the MPE's.
Capt Steven Dewey
Contingency Support Health Physics
Formally the AF Laser Safety Consultant(one of many)
-----Original Message-----
From: George Rawls [mailto:george@ehs.ufl.edu]
Sent: Friday, June 23, 2000 7:03 PM
To: Multiple recipients of list
Subject: Laser calculations
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Perhaps some of the laser experts out there wouldn't mind checking these
calculations/assumptions. Your help will be greatly appreciated. Please
answer me directly unless you believe it is appropriate to answer to the
list.
The problem:
Given a 2 mW laser diode with a 651 nm wavelength and a 5mm aperture and a
human eye very near the aperture, I calculated the irradiance on the eye as
follows: .002 W divided by .385 cm squared, using 7mm as the area(human
dilated pupil as the limiting aperture). Answer equals 5.19x10 to the -3
W/square centimeter.
Also, calculating the MPE for this particular laser, using Table 5 from
Z136.1:
MPE=1.8(t to the 3/4)x 10 to the -3
t=0.25 seconds(aversion response)
MPE=6.36x10 to -4 J/square centimeter divided by 0.25
=2.5x10 to -3 W/square centimeter
Have I made some mistakes, or is the irradiance near the aperture really
more than twice the MPE?
Can I assume the power of the laser(thus the irradiance) will be less than 2
mW at, say, 8 feet from the aperture? Thanks in advance for all help.
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<META HTTP-EQUIV=3D"Content-Type" CONTENT=3D"text/html; =
charset=3Diso-8859-1">
<META NAME=3D"Generator" CONTENT=3D"MS Exchange Server version =
5.5.2651.75">
<TITLE>Laser calculations</TITLE>
</HEAD>
<BODY>
<P><FONT SIZE=3D2 FACE=3D"Arial">Perhaps some of the laser experts out =
there wouldn't mind checking these calculations/assumptions. Your =
help will be greatly appreciated. Please answer me directly =
unless you believe it is appropriate to answer to the list.</FONT></P>
<P><FONT SIZE=3D2 FACE=3D"Arial">The problem:</FONT>
</P>
<P><FONT SIZE=3D2 FACE=3D"Arial">Given a 2 mW laser diode with a 651 nm =
wavelength and a 5mm aperture and a human eye very near the aperture, I =
calculated the irradiance on the eye as follows: .002 W divided by .385 =
cm squared, using 7mm as the area(human dilated pupil as the limiting =
aperture). Answer equals 5.19x10 to the -3 W/square =
centimeter.</FONT></P>
<P><FONT SIZE=3D2 FACE=3D"Arial">Also, calculating the MPE for this =
particular laser, using Table 5 from Z136.1:</FONT>
</P>
<P><FONT SIZE=3D2 FACE=3D"Arial">MPE=3D1.8(t to the 3/4)x 10 to the =
-3</FONT>
<BR><FONT SIZE=3D2 FACE=3D"Arial">t=3D0.25 seconds(aversion =
response)</FONT>
</P>
<P><FONT SIZE=3D2 FACE=3D"Arial">MPE=3D6.36x10 to -4 J/square =
centimeter divided by 0.25</FONT>
<BR><FONT SIZE=3D2 FACE=3D"Arial"> =
=3D2.5x10 to -3 W/square centimeter</FONT>
</P>
<P><FONT SIZE=3D2 FACE=3D"Arial">Have I made some mistakes, or is the =
irradiance near the aperture really more than twice the MPE?</FONT>
</P>
<P><FONT SIZE=3D2 FACE=3D"Arial">Can I assume the power of the =
laser(thus the irradiance) will be less than 2 mW at, say, 8 feet from =
the aperture? Thanks in advance for all help.</FONT></P>
</BODY>
</HTML>
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