MKS Ophir nanoScan Installation and operating instructions

ApplicAtion note
NANOSCAN
COMMON CAUSES OF DAMAGE TO SCANHEADS
& REASONS FOR OUT-OF-TOLERANCE CONDITIONS
INTRODUCTION
Problems you may encounter with a NanoScan
scanning-slit beam profiler are due to either scanhead
damage, or out-of-tolerance conditions.
Scanhead damage can be categorized into two main
types; Laser and Mechanical. Laser damage is the most
prevalent, and results from exposure to lasers with
excessive laser power/energy density, and or high
average power. The damage can be classified into 2
categories, designated “Instantaneous” and “Long-Term”.

•CW beams with Irradiance >~1x106W/cm2
•Pulsed beams with Fluence >~1J/cm2
•Pulsed beams with Peak power >~1x106W/cm2
Long-term exposure limits are given in units of time,
and depend primarily on the beam average power and
wavelength. Long-term heating raises the temperature
of the slit and the drum due to exposure to CW or
Pulsed beams with High Average Power in the range
from approximately 10-100W.
Laser damage includes cut or distorted slits, damaged
detectors, damaged power windows, warped optical
encoder and circuit failure, and cut signal cables.
Mechanical damage typically results from dropping the
scanhead, “touching” the slit substrates, operation in
high particulate environments, and repetitive motion.
Mechanical damage includes bent motor shafts,
distorted slits, plugged slits, and broken signal cables.
Out-of-tolerance conditions are either system related,
including problems associated with circuit or motor
failure, or the scanhead is not appropriate for the
application, such as using a Silicon detector to measure
a 1550nm source, or a 25µm slit for a 10µm beam.
Descriptions of the various damage mechanisms and
out-of-tolerance conditions, and guidelines to avoid
such when possible are presented here.
A Nanoscan exposure limit calculator is available from
the web under the Specication tab at:
https://www.ophiropt.com/laser--measurement/beam-prolers/
products/Scanning-Slit-Beam-Proling-with-NanoScan
Instantaneous damage to slits occurs
due to exposure to:
Slit Aperture Laser Cut Damage
Slit Aperture Laser Burn Damage

Do not expose a NanoScan to a laser beam if the
drum is not spinning! Scanhead damage thresholds
are reduced below specications when the drum is not
spinning, increasing the possibility of damage to the
scanhead.
High Power Caution
When measuring High Power CW or High Energy
Pulsed lasers, do not expose a NanoScan to a laser
beam if the drum is not spinning! The NanoScan drum
does not spin unless the power is ON and the software
is launched. The laser beams incident on the aperture
may cause damage to the slits/pinholes and detector
when the drum is NOT spinning. The slits/pinhole
substrates are thin membranes which can be damaged
if stopped in the beam, and if this occurs, the detector
may also be damaged. Use of a beam dump
is recommended until the drum is spinning!
When running long-term tests with NanoScan,
Congure the PC Power Management to NEVER go
off, and to NOT ALLOW Automatic Updates. These
cause the computer to reboot, closing the NanoScan
program and stopping the NanoScan drum, potentially
subjecting it to the same type of damage.
Power Connection Caution
When unplugging the unit, NEVER unplug the unit
without rst turning off the software and closing the
program. Likewise, when plugging in the unit, make
certain that the program is not running. Failure to do so
may result in the EEPROM being wiped, and the unit
needing to be returned to Ophir-Spiricon for repair and
recalibration.
SCANHEAD DAMAGE
IMPORTANT WARNING!
NanoScan Scanhead

Slit Damage Mechanical
Touching or contacting the slit substrates; for example,
attempting to clean the slit with a cotton swab, or
positioning a source such as an optical ber, so that it
contacts the slit substrate will damage the slits.
Particle contamination results in plugged slits, and
most likely is due to operation in a high particulate
environment, or attempts to clean the slit.
NanoScan Aperture Care
The air slit and pinhole aperture substrates are very thin
and extremely fragile. Any physical contact will likely
damage them. Treat the slits with care; because of their
fragility, never touch them with anything!
Debris such as dust particle can loge in the very ne
openings of the slits or pinholes and obstruct the
passage of the incident beam, especially in the 1.8 µm
slits. This can compromise instrument performance,
resulting in erroneous or inconsistent measurements.
With slits, a few dust particles may or may not be a
problem, depending on the application and measurement
conguration, while contamination by many particles is
more likely to create a problem. With pinhole apertures
a single particle can be disastrous. Therefore, when the
system is not is use, it is recommended that the protective
plastic cap be used to cover the scanhead entrance
aperture to avoid possible contamination. If inconsistent
performance is observed and contamination by debris is
suspected a clean jet of compressed gas may solve the
problem, but excessive pressure may also damage the
apertures. Do not under any circumstances attempt to
clean the apertures with solvents!
If aperture contamination is suspected, it is recommended
that the unit be returned to Ophir-Spiricon for aperture
inspection, cleaning or replacement, and recalibration.
Laser
Laser damage to slits is caused by CW beams with
excessive irradiance, pulsed beams with excessive peak
irradiance, pulsed beams with excessive uence, and
long-term exposure to high average power CW or pulsed
beams. Excessive Laser Irradiance Slit Damage
Do Not Touch Drum
Drum
Slit
Laser Burn Hole Due to
Drum Not Rotating
Slit
Laser Damage
Magnied Image

Consideration for CW Lasers: Irradiance
The irradiance of a CW laser is the power per unit area
in W/cm2, given by the power in Watts divided by the
beam area in cm2.
I(W/cm2) = Power(W) / Beam Area (cm2)
Consideration for Pulsed Lasers:
Peak Irradiance and Fluence
The peak irradiance of a pulsed laser is given by the
pulse energy in Joules divided by the beam area in cm2
and the pulse duration in seconds, usually taken as
the FWHM width. The energy per pulse is the average
power divided by the pulse frequency:
EPulse (J) = Average Power (W) / flaser (Hz)
IPeak (W/cm2) = EPulse (J) / Beam Area(cm2)
The uence of a pulsed laser is the pulse energy per
unit area, in units of Joules/cm2, given by the relation:
F(J /cm2) = EPulse (J) / Beam Area (cm2)
Slit Aperture “Instantaneous”
Damage Thresholds
Damage thresholds are reported in NanoScan User
Guide. Ophir-Spiricon does not warrant damage to slit
apertures and detectors due to damage from high power
lasers. Users of high-power lasers must exercise caution
when measuring their laser beams with their NanoScan.
Slit apertures in NanoScan scanheads are made from
a proprietary metallic alloy. The slit apertures are often
blackened to reduce reectivity and minimize reections
back into the laser cavity. Because of possible slit
damage, Photon performed damage threshold tests on
various NanoScan slit apertures to establish general use
guidelines for prevention of damage to slit apertures. If
you are concerned and still not sure, Photon can provide
aperture material that you can use as a test before using
your source on a NanoScan.
Blackened and unblackened apertures with 1.8μm,
5μm and 25μm nominal slit widths were tested. Tests
were made at laser wavelengths of 532nm, 1.06μm,
and 10.6μm. Damage thresholds are dened here to be
the average laser irradiance at which the onset of visual
damage occurs. The average irradiance is dened as
the average power divided by the beam area at the 1/e²
beam diameter.
All tests were performed under normal NanoScan
operating conditions with the aperture slits moving.
Damage to the slit apertures can occur at much lower
power levels if the laser beam is directed into the slit
apertures while the apertures are stationary.
The tests were performed at laser power levels <3 watts
for short time exposures on the order of 5 minutes. The
damage thresholds that were determined are therefore
applicable only for short time exposures at these power
levels. For high power lasers and long exposure times
the damage thresholds are likely to decrease due to
excessive heating of the apertures and/or possible
ablation that does not manifest itself as visual damage
in short term exposure tests. These effects have not
yet been quantied, so users are advised to exercise
extreme caution when attempting to measure high
power beams for long time intervals. Long exposures
may heat the entire NanoScan and cause other failures.
Note that for the case of blackened slit apertures, the
onset of visual damage occurs when the black material
begins to ablate. This type of damage should not
affect the integrity of the slit but only the reectivity of
the aperture. However, this ablation of material may
contribute to particulate contamination of the slits. Slit
integrity is compromised at the higher laser irradiance
associated with damage to unblackened apertures. This
damage takes the forms of wrinkling or creasing of the
aperture due to thermal stress and scoring of the aperture
due to melting of the metallic alloy. At higher irradiance
and longer exposure times the apertures can be cut.
Recommended upper limits of average laser irradiance
based on the results of the visual damage threshold tests
for short time exposure (~5 minutes) at power levels less
than 3 watts are summarized in Table 1. Values for 355nm
were extrapolated from data at 532nm.

The values of average irradiance listed in the above
table should be used as guidelines to determine if
your operating conditions may cause damage to the
apertures in your NanoScan scanhead for short time
exposure at power levels <3W only. For long term
exposures (>5 minutes) at higher power levels the
damage thresholds may be reduced. Exercise Caution!
NanoScan Operating Space Charts
NanoScan Operating spaces for CW lasers include
the appropriate damage thresholds for nickel and
blackened nickel slit apertures. Figure 1 shows the
Operating Space Chart for a NanoScan/Pyro/9/5; here
there is only one damage threshold line for nickel slits
because blackened slits are not available with pyro
scanheads.
Refer to the NanoScan Installation and Operation
manual for Operating Space Charts for all scanheads.
Fluence exposure thresholds for pulsed lasers are given
in Table 2 for nickel alloy, blackened nickel alloy and
copper slit apertures.
Table 1. Recommended maximum average laser
irradiance incident on blackened and unblackened Nickel
NanoScan slit apertures for short time exposures.
Aperture Slit (µm) Visual Damage Threshold (W/cm2)
355nm 532nm 1064nm 10.6µm
Unblackened 1-2 2x1053x1051x106NA
Unblackened 5-25 2.7x1054x1051.2x1063.5x106
Blackened 1-2 7x1031x1043x104NA
Blackened 5-25 7x1031x1043x104NA
Aperture Visual Damage Threashold (J/cm2)
190-400nm 400-700nm 700nm-3µm >3µm
Unblackened Ni 0.06 1 1 1
Blackened Ni 0.01 0.01 0.01 0.01
Copper NA NA 2.5 5
Table 2. Recommended maximum uence incident on blackened and unblackened
Nickel, and copper NanoScan slit apertures for short time exposures.
Figure 1. Operating Space Chart for the
NanoScan/Pyro/9/5.
Operating Range is at Peak Sensitivity of Detector.
Operating Space is NOT absolute.
THIS CHART TO BE USED AS A GUIDE ONLY

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 gure 2. For pulsed lasers,
specically those in the picosecond and femtosecond
regimes, it is very likely that the peak irradiance exceeds
damage thresholds but the uence 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

Power Window Damage (Laser)
Damage to the power window can occur at levels
below the damage threshold for the slit aperture,
specically for the P75 Wratten Filter option, which has
been discontinued as a product offering.
Detector Damage (Laser)
Detectors can be damaged if the slit aperture is cut or
burned through and the detector is directly exposed.
This damage is avoided by adhering to the guidelines
for slit protection.
Circuit and Encoder Damage (Laser)
Failure of the NanoScan circuitry and the optical
encoder can occur when the scanhead is exposed to
high average power which causes the entire scanhead
to heat. For example, exposure to 180Watts for only a
minute or so can heat the drum to temperatures that
cause warping of the encoder disc and catastrophic
failure. This type of damage is avoided by using only
short exposure times depending on the laser average
power level. Safe operating time depends on the power
as well as the slit material and laser wavelength. Table 4
gives safe operating times for different conditions.
Motor Damage (Mechanical)
Typically motor damage is due to dropping the scanhead,
which results in a bent motor shaft and consequent
catastrophic failure. This type of damage can also occur
during shipping if the scanhead is not packaged properly.
To avoid this type of damage, do not drop the scanhead,
and use at least 2” of rigid foam material or equivalent
packaging if the system is shipped.
Cable (Mechanical)
The signal cable can be damaged due to bending the
cable to too tight a radius, or from repetitive bending
when the scanhead undergoes repetitive motion.
Cable (Laser)
The cable can be severed by a high power laser when
accidentally exposed to high power/energy lasers. This
type of damage is avoided by careful routing of the cable.
Out of Tolerance Conditions
Out-of-tolerance conditions are of two main types: either
system related or use related.
Operation related problems are due to using a scanhead
that is inappropriate for the specic application.
Examples include using a Silicon detector to measure
a 1550nm source, measuring a 10µm spot with a 25µm
slit, or measuring 100µm spot at 1064nm with a Si
detector. These conditions are remedied by the use of
the proper scanhead, which should have been the one
specied at the time of purchase. However, many times
scanheads are then used in other situations, and that is
where problems can arise.
System related problems include items such as
ScanHead EEPROM Communication, Motor Quiescent
Voltage, Motor Speed, and Baseline Offset Voltage.
System related conditions are diagnosed in the software
during system startup, and if encountered the system
will not start and an error message is displayed. There
is nothing that can be done for these conditions except
returning the system for calibration.
Need Additional Help?
Here at Ophir-Spiricon we are committed to the
satisfaction of our customers. If you would like to speak
to a representative about any information contained in
this article, about new products, or to optimize your laser
measurement system for accurate, consistent, and highly
repeatable results, please do not hesitate to contact us.
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Document No 50320-001 Rev D 17 November 2020