Pulsed lasers are complicated.
When you’re dealing with a CW (continuous wave) laser, things are nice and simple. The laser light has a certain power, and that’s exactly what you’re measuring with your laser power meter.
But a pulsed laser is much more complex. Besides power, you also need to worry about pulse energy, frequency, and pulse width (duration).
Now, if you’re looking to measure energy per pulse, you’re going to need to look at all those parameters. (Find out more about measuring laser energy.)
But let’s assume instead that you’re just interested in keeping track of the laser’s average power. Since you’re measuring power, I’m assuming you’re going to use a photodiode or thermal sensor (although you could also use a pyro sensor).
Remember that these sensors don’t even “realize” the laser is pulsing. They don’t care whether there are two 40 μJ pulses per second or one 80 μJ pulse per second. For this reason, frequency and pulse width are irrelevant. There’s no maximum since – on the contrary – a longer pulse or faster frequency just approaches CW, which is fine by us. There’s also no minimum pulse width since we don’t need to worry about the sensor responding to the pulse in time – it’s not going to respond to that particular pulse (in time) but to the average power which gets smoothed out by the thermal sensor.
- Pulse energy:
Although you may have no desire to measure the pulse energy, if it’s too high it could damage the sensor. All Ophir power sensors have a stated maximum pulse energy or energy density that depends on the pulse width.
Specification sheets for photodiode and thermal sensors, indicating the maximum energy levels permitted
2. Low Frequency:
When using a photodiode sensor for a low-frequency pulsed laser beam (under about 100 Hz), it may be difficult to get a steady reading. This is caused by a beat frequency between the laser and the analog-digital converter (which samples at 15 Hz). In many cases this can be alleviated by using the meter’s averaging function.
There will always be more information than you need. There’s too much info on the net, too many emails in your inbox, and yes, too many parameters in the datasheet.
The key is knowing which ones you need.
Ask me in the comment section
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