Perkin-Elmer RamanStation 400 Series, Getting Started Manual

Page: 22 / 98

22 . RamanStation 400 Series Getting Started Guide
The equation for a focused beam, as given here, is used to calculate the nominal ocular
hazard distance (NOHD) for the probe:
2
1
.
4






Π
Φ






=
MPE b
f
NOHD
o
o
Where:
f
o
= Probe focal length (cm)
b
o
= Diameter of laser beam incident on probe focusing lens (mm)
Φ
= Total radiant output power of probe (watts)
MPE =
Maximum permissible expo sure (J cm
−2
)
For a Raman probe
b
o
is 0.254 cm, therefore the above equation can be simplified to give:
2
1
. 442 . 4





 Φ
=
MPE
f NOHD
o
For the wavelength range 700–1050 nm the
MPE
for a 10 second exposure can be calculated
from:
( )
( )
( )
[ ]
4 7 . 0 2
10 10 1 . 10
− −
=
λ
MPE
J cm
−2
Where
λ
is the laser wavelength in micrometers ( µ m). For example, a laser wavelength of
785 nm (0.785
µ
m) will have an
MPE
value of 1.49 × 10
−2
J cm
−2
or 1.49 × 10
−3
W cm
−2
for
a 10 second exposure or longer. Table 2 shows the calculated nominal ocular hazard distance
for 785 nm Raman systems.
Table 2 Nominal Ocular Hazard Distance (NOHD) for 785 nm
Probe focal length/mm NOHD for 100 mW exiting fiber optic probe/cm
7.5 (± 10%) 27.3
NOTE: Other focal lengths are available; contact PerkinElmer for details. In particular, the
use of an ultra-long working distance lens adaptor (L1320071) provides a working
distance of 25 mm. Where different focal lengths are used, the NOHD should be
calculated accordingly.