Q. Does the BeamScan software account for slit width convolution?
For most measurements, this is not necessary, for more details, [see Chapter 2, Slit Convolution and Small Beams].
Q. How do I measure a collimated laser?
Refer to Application Note 220, Measure Divergence & Collimate Lasers.
Q. How do I export data from BeamScan to other programs?
There are three methods to export data. You can save the data as an ASCII file; use data logging; or use the ActiveX capability to communicate with other programs such as Excel or LabVIEW. Refer to Chapter 3 for how to save an ASCII file, Data Logging information and ActiveX Automation. LabVIEW examples are included on your software CD under Automation Folder. We also offer the Optional SDK (Software Development Kit) that includes drivers and DLLs for use with LabVIEW.
Q. How does the BeamScan calculate the beam width?
Photon Inc. uses the ISO Standard moving slit method for beam measurements. In this method, the irradiance profile seen by a very narrow slit is collected. The peak observed is arbitrarily set to 100% and the tail extremes are set to 0%. Beam Size is defined as the spatial width at a particular irradiance clip level and per ISO standards is typically the 13.5% clip level (1/e2); the method is illustrated below.
Clip Level Beam Width
This method is described in the ISO 11146 document and has been used by Photon since 1983. Chapter 2 has a detailed explanation of the entire measurement process.
Q. Can I measure a beam at a large angle of incidence to the scan head?
The BeamScan can measure beams at an angle, but the extent of the angle is dependent on the slit width. The 1.0, 1.8, and 5µm slits are actually narrower than the thickness of the aperture
material, which means that there is a finite angle of incidence at which the
beam will pass through the slits. As the beam's angle of incidence increases the effective width of the slit is reduced, ultimately to zero. This is called vignetting. Once the beam is no longer able to pass straight through the slit to the detector, the slit will serve as an attenuating waveguide. If the beam is sufficiently powerful, it will still be measured; if it is not, the signal may not be strong enough to measure. Generally it is possible to measure beams at 40-45°, however, wider slits are more forgiving of incidence angle than smaller ones. At extreme angles, though, the beam may miss the detector partially or entirely.
Q. How do I measure divergence with the BeamScan?
Refer to Application Note 220, Measuring Divergence and Collimate Lasers.
Q. How do I make M2 measurements with the BeamScan?
The best, fastest, and most accurate way to make M2 measurements is with either the automated ModeScan or RailScan profiler. Refer to Chapter 3, for discussion about the Photon K-Factor Wizard, which allows a quick manual measure of M2 (K-factor).
Specifications
Q. How far is the detector from the front surface?
The measurement plane is the plane of the slit and not the detector location plane. For XY and XYS sized heads the distance is nominally 1.12mm; for other heads, refer to Scanhead Mechanical Dimensions in Chapter 2.
Q. Can my scanhead measure within the UV wavelength?
Yes. Refer to Scanhead Specification Table, Chapter 2, and see the Photo Detector Chart below. Most Silicon detectors will see something in the UV if you have sufficient power. UV enhanced photo detectors are available as an option.
Q. How do I find out the operating range of the scanhead I'm using?
Refer to Operating Space Charts, Chapter 2.2.7.2 in the Manual. These operating spaces are approximate and may not be valid at boundaries due to wavelength, component tolerances and many other variables. Be sure to read the assumptions.
Q. What's the smallest/largest beam I can measure with my unit?
This will depend on the size of the physical aperture of your BeamScan head and the slit size. For the smallest beam a rule of thumb is 4-5 times the slit width; for the largest size, the aperture (e.g., 8.5 mm [front cap] for an XYGET head) limits the size beam that can reach the detector. See Chapter 2 for a discussion of slit width and convolution.
Each model has a lower limit based on slit width. Your scanhead Operating Space Chart will show a value that is 4-5 times the smallest slit width. Spots smaller than 4 microns (13.5% clip level) can be measured using Photon's Near-Field Profilers. We also offer our Microscope Objective Lens Mount Option (H/I) [see Chapter 2], which accepts user provided high quality microscope objectives. Photon can provide a very high quality microscope objective that operates at 100X and NA= 0.95. Call for details. For a more detailed analysis of the measurement of small beams refer to Chapter 2.
Q. What is the size of the slit on my scanhead?
Each BeamScan scanhead has a label that shows the slit size of that particular scanhead. Standard slits are 1 µm, 1.8 µm, 5 µm, and 25 µm. Refer to Scanhead Specifications, Chapter 2, for other slit sizes.
Q. Can I use my scanhead with a pulsed beam?
Yes, if your scanhead was built to work with pulsed beams, Model XYQSW, or if your pulsed beam is in the range generally referred to as quasi-CW (>1MHz repetition rate). Please refer to Scanhead Specifications, Chapter 2.
Q. What is the thread size on the scanhead rotation mount?
Thread size is 1/4-20 or M-6, depending on model. Refer to Scanhead Mechanical Dimensions, Chapter in the Manual.
Operation
Q. My existing unit does not have power meter option; can I order this option?
The Power Option has to be ordered at the time the unit is ordered. Because of labor costs, modifications would be as costly as purchasing a new head with the option installed.
Q. How can I reduce the power in my beam and NOT destroy beam size?
Attenuation can be achieved using high-quality optical components. Care must also be taken to operate below levels where thermal lensing can occur, which will change your measured beam size. With a nearly collimated CW laser, we suggest using a laser-cavity, high quality, dielectric coated plane mirror [flat, no curves] that transmits a small portion of the energy [say 1/2% to 10%]. Photon supplies optical components to meet your needs. Call for details.
Q. Why do I get different readings when I rotate the scanhead?
The primary cause is an elliptical beam. The rotation mount allows you to align the scanhead to the long and short ("fast and slow") axes of an elliptical beam. See Chapter 2, Scanhead Explained and Rotation Mount.
Q. How do I measure elliptic beams?
Rotate the scanhead to find the major and minor axes of the elliptical beam. Be sure to loosen the knurled knob. For more detail refer to Chapter 2, "Measuring Elliptic Beams."
Q. How can I turn off my BeamScan scanhead to reduce motor wear?
Photon's motors are rated at 11,000 rpm; however, they typically operate at 600 rpm. Running the motor continuously may cause a reduction in operating lifetime, but bearings sometimes last longer if they're left spinning. Photon believes that the likelihood of damage from a laser left pointing into a stationary aperture is much higher than the danger of excessive wear to the motor or bearings. If the aperture is stopped in the presence of a high power focused laser beam, it can melt the aperture and even destroy the photocell. In most cases repair costs would exceed motor replacement. Motor wear manifests itself by degrading the position measurement due to position jitter. Beam width accuracy is unaffected by motor wear. In over a decade of use, we have never had a motor freeze or lock due to wear.
That having been said, if you need to turn off your BeamScan, the best way is to power down your PC and unplug the scanhead. You should place the plastic dust cover over the scanhead to protect the slits from dust and finger damage when not in use. Be sure that you do not have a laser beam in the aperture with the drum not spinning.
Q. How does the dual axis scanhead work?
For more information, refer to the Dual Axis Scanhead, Chapter 2.
Q. Does BeamScan measure an absolute beam position?
Not absolute. BeamScan measures relative position of the beam for two orthogonal directions. The beam position is measured relative to the internal optical encoder's start of aperture signal. The aperture window and encoder settings are different unit to unit and will change if the instrument is taken apart and serviced.
Q. How much laser power can I put into the scanhead?
Refer to Chapter 2, Scanhead Specifications and Operating Space Charts. The Operating Space Charts are an approximation and to be used as a guide only.
Q. What power density will damage my slits?
This depends on your beam's wavelength, power and spot size. The black coating is removed before slit damage. A static slit will be damaged at a power level well below the power density limits for a moving slit, and the charts assume a moving drum. This is also the reason that the BeamScan does not have an off switch. Refer to Operating Space Charts, Chapter 2. You can also refer to the damage discussion, Chapter 2, Aperture Damage Threshold Chart, and/or the "Damage Thresholds with High-Power Laser Measurements" PDF.
Q. Do I need to calibrate the power meter each time I turn on the BeamScan?
No. Previous calibration values can be saved and recalled. Refer to Chapters 1 and 3, Relative Power.
Q. Which aperture corresponds to the profile on the screen?
On the Beam Profile screen, the Profile on top corresponds to Aperture 1 and the bottom one corresponds to Aperture 2.
Q. How do I set the I/O Address on the 0180 controller card?
The address has to be set manually on the 0180 controller by moving the I/O Address jumpers. Refer to Chapter 1, BeamScan Card and Scanhead Installation.
Q. Are the increases in gain linear?
No, but they increase in a monotonic fashion; steps are not equal.
Software Installation and Operation
Q. The BeamScan NT software is not working.
Verify that the software you have installed is for the Windows NT 4.0 operating system. The Windows NT 4.0 software cannot be installed properly unless you have Administrator rights; please contact your MIS department.
Q. The software is not recognizing the scanhead.
- Make sure that all connections are firmly established.
- Make sure that the controller card is lodged tightly on the computer bus slot.
- Make sure that hardware and software installations are completed according to Installation Procedures.
- Verify that the software version you have works with the Operating System in your computer. (E.g., running Windows 95 software version on a computer with the Windows NT operating will cause malfunction in your unit).
Q. The software will not run.
- Check to make sure that there is only one instance of BeamScan Software, including Multiple Beam Analysis Software open. More than one BeamScan program open at the same time will cause both to lock up.
- If you have a 0180 card installed, make sure that two cards are not sharing the same address or interrupt. Refer to Chapter 1 for instructions on how this problem can be avoided.
- Verify that you BeamScan Software is compatible with the your computer's operating system.
Q. The system is operating very slowly.
- Make sure the update rate for the particular window is set to its maximum.
- Time Statistics charts may slow down your data collection.
- If the Auto Track is on and the beam is being translated across the entrance aperture, the update rate is slower if the beam is being translated.
- Verify that your computer meets the minimum requirements to run the BeamScan; refer to Chapter 1, Minimum System Requirements.
- Close unnecessary screens and/or other applications for faster performance.
- Be sure that the Global Profile Averaging under the Data Collection Menu is set to a minimum number. The higher the number, the slower the update rate will be.
- If you are using the 2D contour or 3D profile window, you can make the display rate faster by lowering the display resolution and update rate.
Hardware Questions
System
Q. The readings that I am getting are inconsistent.
- Within 1-2% variation in readings for Silicon and Germanium scanhead is normal. Pyroelectric detector scanheads are closer to ±3-4% is normal. Refer to Application Note Measured and Predicted Beam Widths Are Different.
- Make sure your source is stable and not changing.
- If you're getting optical feedback, tilt the scanhead a few degrees, which causes the back reflection from the slits to change.
- Thermal lensing due to attenuation can cause inconsistencies. Be sure you are using high-quality optical attenuators. Test for thermal lensing by slightly translating the suspect component perpendicular to the optical beam. Watch the measured spot size; if spot size changes and begins drifting to a larger value you may have thermal lensing.
Q. Beam width measurements on 2 different BeamScans get two different results.
- Check the Operating Space Charts for each BeamScan.
- If they are the same type scanhead, one or both may need calibration.
- Unit-to-unit repeatability is within the ±2% range.
- Consider purchasing Photon's BeamTest Fixture, which includes a calibration head, a standard laser, and several lenses.
- It is not easy to get two instruments in the same exact XYZ and theta (q) location. Mechanical mounts to locate the beams are not stable or tight, especially true when working with beam sizes less than 25 microns.
- Check your instrument tolerance. You may have scanheads at opposite extremes.
- You must measure at the same exact measurement plane and scan direction.
- Refer to Application Note, Measured and Predicted Beam Widths Are Different.
Q. What is normal in terms of variation in measurement?
Unit-to-unit repeatability and within-unit repeatability of the BeamScan is expected to fall within the ±2% range on beam size. Position measures are in the few micron range or better when sampling at 0.14 or 1.4 micron. This can be improved with averaging to sub-micron values. See Technical Notes, "Beam Widths, Standards and Calibrations" and "NanoScan and BeamScan Reliability and Long Term Service."
Q. The readings I'm getting are all saturated. How do I fix this?
First, check the gain setting (See Chapter 3, Setup Menu). If it's set at minimum, then check the Operating Space Chart (Chapter 2) for your BeamScan; the laser beam being used may not be within the operating range of the scanhead. If the scanhead has a manual gain control switch, it might be set too high. Select a lower Gain setting (see Chapter 2, Scanhead Explained for the Gain Switch illustration).
Q. I'm getting intermittent signals on my BeamScan.
- Your laser could be modulating; check your laser with our power meter or a photo diode, or try a different laser. BeamScan has a very wide bandwidth, so you may observe rapid time variations.
- Check your BeamScan cable, which can wear out over time.
Q. My unit is giving out inaccurate readings; what is causing it?
Refer to Application Note Measured and Predicted Beam Widths Are Different.
Q. My Measured and Predicted Beam Widths are different.
See Application Note Measured and Predicted Beam Widths are Different.
Q. I have a dual-axis scanhead, but I'm seeing only one profile.
- The Beam Profile might be set to operate and collect data from one aperture only. Refer to Chapter 3, Data Collection Menu to change this setting.
- If your beam is extremely elliptic, only one profile can be displayed, due to the high ellipticity ratio. For further discussion on measuring elliptic beam, refer to Chapter 2.
Controller
Q. My unit stopped working.
Be sure everything is connected properly and power is getting to your unit. If it still is not operating, look to see if the scan drum with the slits is spinning. If yes, reboot your system and reset all screen settings to default values. Check to see that update rates are reasonable and not one hour between data samples.
Q. Noise/oscillation problem on the readings.
- Check that the beam being used has enough power and is within the operating range of the scanhead. Refer to Chapter 2, Operating Space Charts.
- Possible laser feedback from the instrument can cause the laser cavity to go into oscillation. Refer to Chapter 2, Back Reflections.
- Enable the filtering function or Profile Averaging; refer to Chapter 3, Data Collection Menu.
- Check for Electro-Magnetic Interference (EMI).
Scanheads
Q. The drum with slits in the scanhead is not rotating.
- Verify that the scanhead cable is connected securely to the BeamScan controller.
- Scanhead may have experienced a large mechanical shock, which can cause the assembly to stop spinning.
Q. The scanhead cannot find the beam
- Be sure the source is on and the beam size, wavelength and power are within the operating range, See Operating Space Charts, Chapter 2.
- Possible conflict between board and memory settings; refer to Chapter 1 for discussion on memory jumper setting on the board.
Q. Motor on scanhead is spinning slowly.
- For a Model 3088, it is normal for the BeamScan to spin slowly until the system is booted up.
- Scanhead may have experienced a large shock.
Q. The scanhead won't fit into the rotation mount.
This is an extremely tight fit; carefully align and try again. Insert the scanhead from the front end without the label.
Q. The scanhead will not rotate in the rotation mount.
Loosen the knurled knob on the scanhead to rotate.
Power Meter
Q. The power meter is not calibrating properly.
- Make sure that the beam has been found before attempting to perform the power calibration.
- It is possible for a power calibration to fail with a Power Saturated error when in fact the beam power is not excessive. This occurs when the AutoFind selects a head gain that is too high for the power card to work with. A possible solution to this problem would be to go into Board Settings and manually lower the head gain and then re-try the calibration procedure.
- Could also be caused by exceeding the operating space of the power meter, which may be lower than the profiler's operating space.
Q. The power meter card does not seem to be working; I'm not getting any power readings.
- Verify that your scanhead has the /PWR option on the label.
- Verify that a power card is installed in your computer. Check the connections. Make sure that the power card is installed correctly, and is connected to the scanhead. Review Chapter 1, Power Card Physical Setup/Cable Connections.
- The Power Option needs to be calibrated before it can provide power measurements; refer to Chapter 1, Power Option Calibration Procedure.
Q The power reading is lower as the angle of incidence is increased. Why?
The attenuator used absorbs light through the thickness and as the angle of incidence increases, the power decreases. In addition, the sensor will decrease its response. Perform calibration in the same configuration as you intend to use the power meter.
Software Error Messages (in alphabetical order)
Error reading BeamScan card
Please make sure that your BeamScan is plugged in and that the card is properly and firmly seated in your computer. Check that you do not have any address or interrupt conflicts with other plug-in boards, and that all jumper selections on the BeamScan board correspond to the software selections. Make sure that the program has not been activated twice.
Invalid BeamScan card address selected
Please make sure the correct board address has been selected through the BeamScan Configuration program.
Invalid drum rotation speed selected
Please make sure the correct head speed has been selected through the BeamScan Configuration program.
Invalid memory size
Please make sure the correct memory size has been selected through the BeamScan Configuration program.
No Peak was Found
Scanhead being used is not designed to work with the laser beam being measured. A GE model will not see a UV source. An XYFIR pyroelectric detector will not see a milliwatt beam. Verify the Operating Range and Specifications in Chapter 2 for your particular scanhead.
Check to see if your laser is on or if you have a low power beam.
Try to find beam with the Auto Gain/AutoTrack on.
Software being used is not compatible with the operating system of the computer. For example, running Windows 95 software version on a computer running on Windows NT 4.0 operating system.
No Power
The signal in the power card is too low and no measurements can be made. Increase the head gain then decrease the signal gain to avoid profile saturation.
No Power Card Detected
Unit does not have the Power Card installed or the Power Card was not configured properly. If a power card was not purchased with the unit, un-install the power card in the software setup; refer to Chapter 1. If you purchased the power card, refer to Chapter 1.3, Power Option installation Instructions. Note: Your scanhead will be labeled with /PWR if the Relative Power Option was ordered with your unit.
Peak is saturated
The instrument gains are at their minimum and the profiles are still too high. If you have a BeamScan head with a manual head gain switch, try a lower gain setting. If this is not possible, or if you have an automatic head, decrease the laser power.
Peak is too low
The instrument gains are at their maximum and the profiles are still very small. If you have a BeamScan head with a manual head gain switch, try a higher gain setting. If this is not possible, or if you have an automatic head, increase the laser power. You need more laser power for accurate measurements.
Peak is too narrow
The beam width decreased so much that the sampling resolution has to be changed. The program will restart "Scanning for beam..." if AutoTrack/AutoGain is selected.
Peak is too wide
The beam width increased so much that the sampling resolution has to be changed. The program will restart "Scanning for beam..."
Peak lost
The beam has moved so much in the aperture, that the program lost track of it, although AutoTrack is on. It will restart "Scanning for beam..."
Power card is saturated
The signal in the power card is saturated. Please lower the head gain. Then increase the signal gain to avoid a too low profile.
Power is low
Although the power can still be measured, the power card is working at its limits. Please select a higher head gain for more accurate measurements.
Power is near saturation
Although the power can still be measured, the power card is working at its limits. Please select a lower head gain for more accurate measurements.
Scanning for beam...
The software is trying to find a beam in the aperture. Please wait.
Unknown head or no head connected
Make sure the BeamScan head is not connected to the game port on your computer. Also remember to turn off your computer before attempting to connect or disconnect the head.
|
