Laser Security

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Laser Security

• By Emile SCHWEICHER,
• OMRA,RMA, Brussels
• emile.schweicher_at_gmail.com

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Laser Security

• We are not concerned with the dangers for the
  skin !
• Well only investigate the dangers for the eye
  which arise
• from picture aside a 1mW laser at 6m is 10
  times more dangerous than the Sun !
• This danger is described in
• Belgian Army Reglement G901 (recently updated)
• STANAG 3606 LAS (STANAG means Standardization
• NATO Agreement) .
• There exists also Agreement FINABEL
• H-FIN/SEC/23.502-H issued 05 Aug 1983 .
• The danger for the eye is a function of
• The emitted power (obvious!)
• The wavelength this is less obvious but will
  be
• demonstrated by next slide describing this
• danger in various wavebands

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The danger is given by the class the higher the
class number the more dangerous the laser.The
class shall be indicated by a sticker on the
laser. Class 3 and 4 lasers may only be turned
ON by means of a removable key. Class 2 exists
only for visible lasers. Class 1 single not
dangerous class!
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Typical laser safety glasses compulsory in each
lab workshop
Very recent (Oct 07) new classification in Europe
in US ANSI Z136 standard
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An Overview of the LED and Laser Classification
System in EN 60825-1 andIEC 60825-1
In 2001 the standard governing the safety of
laser products in Europe (EN) and Internationally
(IEC), was substantially revised and the
Classification system was overhauled. This
resulted in the introduction of three new laser
classes (1M, 2M and 3R) and the abolition of
Class 3A. Below is a brief description of each of
the current laser classes.The 60825-1 standards
apply equally to lasers and LEDs. In most places
we have used the word "laser", but it can be
replaced by "LED". Generally speaking LEDs would
be in the lower Classes (1, 1M, 2, 2M, 3R), but
very exceptionally may be Class 3B. At the time
of writing we are not aware of any Class 4 LEDs.
In 1M 2M , M comes from Magnification. The
phrase "eye-safe" is used below. Please note that
"eye-safe" is applicable to the whole optical
spectrum from 180nm to 1mm wavelength, not just
in the retinal hazard range of 400nm to 1400nm.
Outside the retinal hazard range there is
potentially a hazard to the cornea. A wavelength
outside the retinal hazard range is therefore not
automatically eye-safe!Class 1This class is
eye-safe under all operating conditions. Class
1MThis class is safe for viewing directly with
the naked eye, but may be hazardous to view with
the aid of optical instruments. In general, the
use of magnifying glasses increases the hazard
from a widely-diverging beam (e.g., LEDs and bare
laser diodes), and binoculars or telescopes
increase the hazard from a wide, collimated beam
(such as those used in open-beam
telecommunications systems).Radiation in classes
1 and 1M can be visible, invisible or both.Class
2 These are visible lasers. This class is safe
for accidental viewing under all operating
conditions. However, it may not be safe for a
person who deliberately stares into the laser
beam for longer than 0.25 s, by overcoming their
natural aversion response to the very bright
light.
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Class 2M These are visible lasers. This class is
safe for accidental viewing with the naked eye,
as long as the natural aversion response is not
overcome as with Class 2, but may be hazardous
(even for accidental viewing) when viewed with
the aid of optical instruments, as with class
1M.Radiation in classes 2 and 2M is visible, but
can also contain an invisible element, subject to
certain conditions.Classes 1M and 2M broadly
replace the old class 3A under IEC and EN
classification. Prior to the 2001 amendment there
were also lasers which were Class 3B but were
eye-safe when viewed without optical instruments.
These lasers are Class 1M or 2M under the current
Classification system.Class 3R (R from low
Risk) Radiation in this class is considered low
risk, but potentially hazardous. The class limit
for 3R is 5x the applicable class limit for Class
1 (for invisible radiation) or class 2 (for
visible radiation). Hence CW visible lasers
emitting between 1 and 5 mW are normally Class
3R. Visible class 3R is similar to class IIIA in
the US regulations Class 3BRadiation in this
class is very likely to be dangerous. For a
continuous wave laser the maximum output into the
eye must not exceed 500mW. The radiation can be a
hazard to the eye or skin. However, viewing of
the diffuse reflection is safe.Class 4This is
the highest class of laser radiation. Radiation
in this class is very dangerous, and viewing of
the diffuse reflection may be dangerous. Class 4
laser beams are capable of setting fire to
materials onto which they are projected. Any
laser product of a given Class may contain
'embedded' lasers which are greater than the
Class assigned to the product, but in these cases
engineering controls (protective housings and
interlocks) ensure that human access to radiation
in excess of product Class is not possible.
Notable examples of this are CD and DVD players
which are Class 1 laser products while containing
Class 3R or Class 3B lasers and laser printers
which are Class 1 laser products but contain
Class 4 embedded lasers.
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• Note- for a product to be classified correctly,
  it must be tested at the maximum output
  accessible under reasonably foreseeable
  single-fault conditions (e.g., in the drive
  circuitry). A non-M class product must pass both
  Condition 1 and Condition 2 of Table 10 in IEC/EN
  60825-1, and an M-class product (which by
  definition has failed either Condition 1 or 2)
  must pass the irradiance condition in the same
  table.
• Generally speaking lasers are point sources while
  LEDs are extended sources. Extended sources have
  higher power limits than point sources for a
  given laser Class. Therefore a visible LED
  emitting 10 mW may be Class 2, while a visible
  laser pointer of the same power would be Class
  3B. NB Laser pointers above Class 2 are banned
  for sale to the public by trading standards.
• CW Continuous Wave - i.e. not pulsed
• Diffuse reflection the reflection of
  radiation from a matt surface such as a wall
• Extended source having an apparent source
  size with angular subtense of greater than 1.5
  mradian
• Optical instruments binoculars, telescopes,
  microscopes, magnifying glasses (but not
  prescription glasses)
• Point source having an apparent source
  size with angular subtense of less than 1.5
  mradian

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More about various laser safety standards
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Typical laser protection glasses
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Laser classification scheme
The laser subdivision in 4 classes is
evidently a function of power and wavelength
Analysis of STANAG 3606

• EMP MPE maximum
• blootstelling maximum
• bestralingsdosis Maximum
• Permissible Exposure
• Exposition Maximum Permise
• is a power density (W/m²) for
• CW (Continuous Wave) lasers
• is an energy density (J/m²)
• for pulsed lasers. We consider
• the case of pulsed lasers for CW
• lasers it suffices to replace energy by power.

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2. DOCN NOHD NKO Nominale Kritische
Oogafstand Distance Oculaire Critique
Nominale Nominal Ocular Hazard Distance . This
is the laser safety distance! A laser safety
officer shall only be interested by the NOHD.
Unfortunately , the NOHD is not given by the
STANAG 3606 nor by G901 ! STANAG G901 only
give the MPE (or EMP). So we must be able to
compute the NOHD out of the MPE !
a and b are the extreme rays of the laser beam
like all other laser rays they intersect in the
center of the waist (waistcercle de gorge
keelcirkel)
a
Clearly , the NOHD is
the radius of the sphere where the energy
densityEMP
Consequently the center of the waist behaves as
the origin of a spherical wave involving an
energy density proportional to 1/R² .
NKO
b
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Fig.V.65b
Following formula gives the NKODOCNNOHD
P is the energy in one laser pulse and d is the
beam diameter at laser output F 2? is the
laser divergence.
A large value of the NOHD means a dangerous
laser . Formula shows that a large NOHD
corresponds to a small EMP. Consequently a
dangerous laser is characterized by a small
value of the EMP ! EMP varies as PRF-1/2 , where
PRF is the Pulse Repetition Frequency.
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Computation of the NOHD
Fig.V.66
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Using a sight (binoculars) multiplies the NOHD
by the magnification M
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Fig.V.67
Table V.4
Excerpt of STANAG 3606
True eye safe is in the deep pit 1.4µ-1.57µ !
In table V.4, the ratio between 1st and 4th row
of the EMP is 2000 ! The ratio between 4th 5th
row is 100 thus the ratio between 1st and 5th
is 200,0002.105!
Raman laser is obtained by a Raman effect
(NLO) shifting NdYAG 1.064µ wavelength through a
cell filled with CH4 providing so a coherent
output radiation at 1.54µ same ? directly from
Erglass or ErYAG lasers. Better OPO!
NLONon Linear Optics
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LANTIRN TGP (Targeting Pod)
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OPO enables to obtain any eye safe wavelength
out of the NdYAG 1.064µ wavelength
c. OPO-based laser designator of the Belgian F-16
LANTIRN TGP (Targeting Pod)
OPOOptical Parametric Oscillator OPO is
essentially a NLO (Non
Linear Optics) crystal crystal rotation ensures
tunability of output wavelength
Fig.42BIS. Working principle of the laser
designator of the Belgian LANTIRN Targeting Pod,
radiating "eye safely" 1.54µ in peace time, and
1.064µ in war time. The pumping laser diodes
radiate at 808 nm, i.e., in the middle of the YAG
absorbing band

• Flash lamp pumped NdYAG laser features ?
  0.7, PRF ? 20 Hz
• (laser) diode pumped NdYAG laser features ?
  10, PRF ? 5 kHz, because the laser diode, being
  much more monochromatic, extends less out of the
  YAG absorbing band centered at 808 nm
• The LANTIRN (low Altitude Navigation Targeting
  by IR at Night) TGP comprises also a LWIR
  Targeting FLIR (with small FOV) and a TV camera.

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• F-16 with
• the LANTIRN TGP under its air intake
• the typical seeker of a laser guided bomb
• one pylon tank (not stealthy at all) and one tip
  carriage
• blending (fuselage merges into the wings) and
  Au-coated canopy two stealthy features.

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How the NOHD can be reduced to 0 use a beam
expander !
m²)
)
D is the beam diameter at the laser output , D
is the beam diameter at the distanceNOHD. Use a
beam expander with magnification MD/D is
the half divergence without beam expander
is the half divergence with beam expander
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The two kinds of beam expanders les 2 afocaux
de 2 bundelverbreders
Galilean Beam Expander (for HEL)
LASER
Eyepiece
Keplerian beam expander
LASER
Magnification M fobj/ IfocI . The laser
beam diameter is multiplied by M while the
laser divergence is divided by M .
Keplerian beam expander with pinhole PH as
low- pass spatial filter
Eyepiece