Table 3. Slit Aperture Exposure Time Limits (minutes)
Table 4. Exposure Time Limits for Nickel Alloy and
Copper Slit Apertures (minutes)
These values are also shown in the Pulsed Damage
Threshold curves given in figure 2. For pulsed lasers,
specifically those in the picosecond and femtosecond
regimes, it is very likely that the peak irradiance exceeds
damage thresholds but the fluence per pulse is very low.
In this case it is unlikely that instantaneous damage will
occur, but long term damage from micromachining is
likely. In this case,
Proceed with caution!
Long term Slit aperture Heating
exposure Limits
The long term exposure limits for slit aperture heating
are based on a heating model where all the laser power
goes into heating the slit aperture, and the time limit
that is necessary to reach the melting point of the slit
material, either nickel alloy or copper. When the slit
heats the Instantaneous Damage thresholds decrease.
The model provides conservative values for the time
limit because it neglects thermal conduction into the
drum. For reported times >5minutes, it is generally
safe to operate with continuous exposure, but caution
is advised. Exposure time limits for nickel alloy and
copper slit apertures are given in Table 3.
Long term drum Heating exposure Limits
The long term exposure limits for drum heating
are based on a heating model where all the laser
power goes into heating the drum, and the time
limit necessary to reach 100°C. The model provides
conservative values for the time limit because it
neglects convection cooling of the spinning drum. For
reported times >5minutes, it is generally safe to operate
with continuous exposure, but caution is advised.
Exposure time limits for nickel alloy and copper slit
apertures are given in table 4.
Wavelength
354.7
532
1064
10600
Material Power (W)
time (minutes)
Nickel
1
22
32
46
645
10
2.2
3.2
4.6
64.5
100
0.22
0.32
0.46
6.45
Copper
1
25
38
500
746
10
2.5
3.8
50
74.6
100
0.25
0.38
5
7.46
Wavelength
354.7
532
1064
10600
(Power W)
time (minutes)
1
300
300
425
1060
10
30
30
42.5
106
100
3
3
4.25
10.6
Figure 2. Pulsed Laser Damage Thresholds for nickel
alloy and copper slit apertures
