How to Find the Perfect Laser Beam Profiler

As there are several different types of laser (Figure 1), the need for many different profilers to oversee the range of lasers has increased. Currently, there are cameras and scanning slit profilers, which possess a number of options for different types of detectors. This article deals with questions  that users need to ask to locate the right laser beam profiler for their laser and application.

Laser beam profilers

Figure 1. Laser beam profilers

Wavelength

The laser’s wavelength establishes the kind of detector the beam profiler should possess. They are as follows:

  • Si – Visible, NIR
  • Pyroelectric – UV, IR, THz
  • Ge, InGaAs – NIR

In comparison to pyroelectric and InGaAs varieties, Si and Ge sensors are less expensive.

Beam Size

In the case of large beams, users require a profiler with an adequately large aperture. However with small beams, many things need to be considered. If a camera is being used, the beam should be no less than 10 pixels wide to provide excellent accuracy. In the case of a scanning slit, the beam should have a minimum of four times the slit width, providing a minimum of approximately 8 µm. For both small and large laser beams, reducing/expanding optics enable the use of previously unsuited profilers.

Power

It is a fact that each beam profiler has a saturation level and a damage threshold. If the damage threshold is exceeded, damage may occur, while saturating the profiler may decrease measurement precision. Cameras possess a very low saturation level, which means that only the lowest power lasers would require some form of attenuation. The attenuation has a damage threshold, which would require users to have a combination of beam splitters, ND filters, and other optics to profile the beam properly.

Scanning slits often measure up to kilowatts of power minus the attenuation. This is because the spinning slit only allows the beam to hit the detector for a minimum amount of time, efficiently reducing the beam’s average power by that factor. For very high lasers, scanning slits will require some kind of attenuation.

Pulsed or CW

Cameras operate using both CW and pulsed lasers. Scanning slits function only if the laser is pulsing at a low rep rate. The entire operation works fine at higher rep rates.

The line between high and low rep rate is based on the size of the beam and the scan rotation speed. The reason behind this is a bit complex, however the outcome is fairly simple. Table 1 shows how fast a laser has to pulse to enable scanning slit use.

Table 1. Minimum beam size per pulse frequency

Minimum Beam Size per Pulse Frequency
NanoScan Normal Drum Large Drum (HP)
Rotation Rate (Hz) 1.25 2.50 5.00 10.00 20 1 25 2.50 5.00 10.00
Slit speed (um/msec) 116.63 233.25 466.50 933.01 1866.01 233.25 466.50 933.01 1866.01
Data Points per Profile 15 15 15 15 15 15 15 15 15
Pulse Frequency (kHz) Minimum Beam diameter in µm Minimum beam diameter in µm
1 1749 3499 6998 13995 27990 3499 6998 13995 27990
2 875 1749 3499 6998 13995 1749 3499 6998 13995
3 583 1166 2333 4665 9330 1166 2333 4665 9330
4 437 875 1749 3499 6998 875 1749 3499 6998
5 350 700 1400 2799 5598 700 1400 2799 5598
6 292 583 1166 2333 4665 583 1166 2333 4665
7 250 500 1000 1999 3999 500 1000 1999 3999
8 219 437 875 1749 3499 437 875 1749 3499
9 194 389 778 1555 3110 389 778 1555 3110
10 175 350 700 1400 2799 350 700 1400 2799
11 159 318 636 1272 2545 318 636 1272 2545
12 146 292 583 1166 2333 292 583 1166 2333
13 135 269 538 1077 2153 269 538 1077 2153
14 125 250 500 1000 1999 250 500 1000 1999
15 117 223 467 933 1866 233 467 933 1866
16 109 219 437 875 1749 219 437 875 1749
17 103 206 412 823 1646 206 412 823 1646
18 97 194 389 778 1555 194 389 778 1555
19 92 184 368 737 1473 184 368 737 1473
20 87 175 350 700 1400 175 350 700 1400
21 83 187 333 666 1333 167 333 666 1333
22 80 159 318 636 1272 159 318 636 1272
23 76 152 304 608 1217 152 304 608 1217
24 73 146 292 583 1166 146 292 583 1166
25 70 140 280 560 1120 140 280 560 1120
50 35 70 140 280 560 70 140 280 560
100 17 35 70 140 280 35 70 140 280
150 12 23 47 93 187 23 47 93 187

Conclusion

While there is no universal solution to fit everyone's specific needs, users must consider the above questions and discover which beam profiler is appropriate for their applications, or alternatively they can discuss this further with a sales engineer.

This information has been sourced, reviewed and adapted from materials provided by Ophir Optronics Group.

For more information on this source, please visit Ophir Photonics Group.

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