Re: Laser lunacy
From: canopus56 (canopus56_at_yahoo.com)
Date: 01/03/05
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Date: 3 Jan 2005 12:04:18 -0800
Chris L Peterson wrote:
> A telescope is a collimator. But remember that a telescope is defined
as the
> combination of an objective and an ocular- you need both. Simply
aiming a laser
> at the primary mirror will result in a beam that is more divergent
than the
> laser itself.
The following may be of interest to those wishes to expand their
knowledgebase with respect to this ongoing discussion of the hazards of
red lasers in telescope colliminators and green pointer lasers used for
astronomical instruction. I have no special knowledge in this area.
The following are some points that I gleaned from web reading:
The class of lasers we are discussing are Class IIIA - 1-5mW. OSHA
Technical Manual, undated. For example, Howie Glatter's SkyPointer
laser. Glatter 2005. Laser pointers of energy below 2.5 mW/cm^2 (your
typical red pointer laser) are required to bear a "CAUTION" tag.
Lasers above 2.5 mW/cm^2 (your typically green laser pointer) bear the
"DANGER" tag.
The basic industry safety standard is ANSI Z136.1, Safe Use of Lasers,
and Z136.6 Safe Use of Lasers of Outdoors.
The ANSI Z136.1 standard formed the basis, in part, for a later Federal
Aviation Administration (FAA) laser safety exposure study, which
quantifies the hazard effect of persons inadvertently pointing lasers
at pilots. FAA 74002D. This study led to a regulation creating
laser-free zones around airports.
This regulation did not result from the hazard of laser pointers, but
rather the use of high power lasers in outdoor entertainment laser
light shows by theme parks, casinos and sports stadiums. Nakagawara,
undated. For example, through 1993 at Las Vegas's McCarran airport near
the Las Vegas Casino strip, 53 pilots reported being hit by inadvertent
laser strikes from such shows. "A potentially serious condition exists
when the laser flash wipes out the dark adaptive state of the pilot.
Partial recovery of dark adaptation is normally achieved in 3 to 5
minutes, but full adaptation typically requires 40-45 minutes. During
this period, the pilot would be visually compromised making night
flight operations difficult or impossible." Nakagawara, undated. The
result was the FDA order, which sought to create a laser-free zone
around airports.
Laser hazard data and terminology developed to address that problem can
be extrapolated to the lower power Class IIIA lasers used by amateur
astronomers. Two useful terms are the maximium permissible exposure
(MPE) - meaning the biological effect on the eye at various cumulative
exposures to laser energy, and the nominal hazard zone (NHZ) - meaning
a space within which the level laser light exceeds the MPE.
An excerpt from the following Rockwell Laser Industries article
summarizes the nominal hazard zone (NHZ) distances for Class IIIB
lasers. Rockwell, undated. Note that Class IIIB lasers begin at 5 mW of
power - the upper limit of Class IIIA red and green lasers being
discussed in this usenet group:
================================================
Excerpt from Rockwell "Safety Recommendations of Laser Pointers"
The NHZ associated with open-beam Class IIIB and Class IV laser
installations can be useful in assessing area hazards and implementing
controls. The summary in Table 1 shows the magnitude of the NHZ's for a
visible frequency laser pointer emitting 5mW:
Table 1
Nominal Hazard Zones for Visible Diode Pointers
Power: 5 mW - Divergence: 1 mr - beam size: 2 mm
Based on: FAA 74002D Outdoor Laser/High Intensity Light Demonstrations
Bioeffect MPE Level * Nominal Hazard Zone
Condition (W/cm2 ) (feet)
BLINK REFLEX 2.6 x 10-3 51
FLASH-BLINDNESS
/AFTERIMAGE 100 x 10-6 262
GLARE 5 x 10-6 1,171
"NO EFFECT" 50 x 10-9 11,707
[ MPE = Maximum premissible exposure ]
The different visual effect "MPE" criteria used in the NHZ computations
in Table 1 were are based upon the U.S. Standard for the Federal
Aviation Administration: FAA 74002D Outdoor Laser/High Intensity Light
Demonstrations which provide a numerical basis for the various
bioeffect criteria [6].
(6) FAA 74002D Outdoor Laser/High Intensity Light Demonstrations: From
Chapter 34: Outdoor Laser/ High Intensity Light Demonstrations, Federal
Aviation Administration
=================================================
Appendix B in this excellent Rockwell article includes a list of
reported "laser pointer" incidents in the U.S. and the U.K.
The above data concerns the hazard to persons using unenhanced vision.
To my knowledge, no one has worked through the physics of what happens
when a Class IIIA low-power red laser or a green laser pointer
inadvertently strikes, let's say, an 11" SCT or an 8" DOB.
As "Uncle Bob" pointed out in another thread, the military has done a
great deal of work on the optical density of safety filters that
binoculars and telescopes need in a battlefield environment. The modern
battlefield is thick with high power targeting lasers from tank sites
and target designators.
But what is the concentrative (or dilutive) effect of light grasp and
magnification seen in civilian telescopes inadvertently struck by
civilian Class IIIA red or green laser pointers, given the biological
effects and maximum permissible exposure (MPE) limits in Table 1?
- Canopus56
References:
American National Standards Institute, American National Standard for
the Safe Use of Lasers: ANSI Z 136.1 (2000) <<
http://webstore.ansi.org/ansidocstore/product.asp?sku=ANSI+Z136%2E1%2D2000
>>
American National Standards Institute, American National Standard for
the Safe Use of Lasers Outdoors: ANSI Z 136.6 (2000) <<
http://webstore.ansi.org/ansidocstore/product.asp?sku=ANSI+Z136%2E1+and+Z136%2E6+Combination+Set
accessed 1/5/2005 >>
ANSI, generally << http://webstore.ansi.org/ansidocstore/find.asp?
accessed 1/5/2005 >>
FAA 74002D Outdoor Laser/High Intensity Light Demonstrations: From
Chapter 34: Outdoor Laser/ High Intensity Light Demonstrations, Federal
Aviation Administration.
Glatter, H. 2005. Skypointer Website. << http://www.skypointer.net/
accessed 1/5/2005 >>.
Nakagawara, Van B., OD and Ronald W. Montgomery. Undated. Laser Light
Exposure: What is Being Done to Protect Pilots and Aviation Safety. <<
http://www.sportmedpraxis.com/Laser.htm accessed 1/5/2005 >>.
OSHA Technical Manual, Laser Hazards, Section III, Chapter 6. Para.
IV(B)(2)(d). << http://www.osha.gov/dts/osta/otm/otm_iii/otm_iii_6.html
accessed 1/5/2005 >>
Rockwell, Jr., James R., and Ertle, William J., Rockwell Laser
Industries, Moss, C. Eugene, National Institutes of Occupational Safety
& Health. Undated. Safety Recommendations of Laser Pointers. <<
http://www.rli.com/resources/pointer.asp undated, accessed 1/5/2005 >>
(Highly-recommended reading).
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