[SOLVED] Need help with co2 laser tube switching speed.

I have a 20W co2 laser tube (from some medical equipment) and a power supply for 40W tube (from Chinese laser engraver).

The laser tube works fine. It has about D=3.6 mm laser beam.

But I am wondering how fast I can switch on/off my laser tube. My power supply can switch on/off the laser tube with frequencies about 1 kHz. But it is not enough for me.

In the internet I found out that co2 laser tube (by it’s nature) works as low pass filter and you can not switch it on and off with frequency above some fc=~5khz. Some RF excited laser tubes can work faster, but not much faster.

I will explain why it is not enough for me to have 1 khz switching frequency.

I am trying to do a fast engraver based on “flying mirror approach”. My mirror-lens system can fly back and forward with speed up to 3000 mm/s. Let say I want to engrave some picture on PMMA with 508 dpi resolution (20 points per mm). In order to achieve this, my laser should be capable of switching on and off with frequency = 3000 * 20/2 = 30 000 hz.=30khz (the pulse with should be about 16 us).

With my current power supply I can do this job lowering the laser-output power and speed to 50 mm/s speed.

So, the main question: Are there a way to switch on and off the co2 laser tube with frequency up to 100 khz? I know that there are (on the planet) co2 laser engraving systems with higher speed and resolution that I wrote about above.
Are there any acousto-optic deflectors for co2 lasers?

Thank you very much.

I think you need an optical switch. I cannot remember what the correct term for it is. Maybe a "spatial light modulator". Flüssigkristall-Lichtmodulatoren | Optical Systems | JENOPTIK AG

Liquid crystal based ones are probably too slow but I am sure there are other technologies around which are very fast (but could be expensive).

Keith.

Thank you for the reply.

But unfortunately all commercially available SLM’s and ALM’s I know about designed for visible spectrum and near infrared spectrum.


Oh. I still need help.

keith1200rs said:

I think you need an optical switch. I cannot remember what the correct term for it is. Maybe a "spatial light modulator". Flüssigkristall-Lichtmodulatoren | Optical Systems | JENOPTIK AG

Liquid crystal based ones are probably too slow but I am sure there are other technologies around which are very fast (but could be expensive).

Keith.

Click to expand...

I have not worked with high-power lasers but if your power supply can switch on/off with a 5 kHz rate, I think you can try to achieve 16 us pulses by modifying the power supply modulator.
In microwave radar, high-power triodes and tetrodes are used to generate pulses as short as 0.1 us. You need a high-voltage DC source (and you have one), then, to form a good rectangular pulse, a shorted section of a coaxial cable is needed in which the reflection "extinguishes" the discharge in the laser tube. You can also discharge a suitable HV capacitor by the keyed triode.

The design also depends on the pulse frequency (dissipated power). I used a 10 nF/20 kV capacitor switched by an old HV vacuum tube to make a microwave magnetron send one 3 us pulse after another. I would consult a radar technician or local radio amateurs how best to make an experiment.

Using a Kerr switch is possible but expensive, also your high power output is a problem.

---------- Post added at 19:23 ---------- Previous post was at 19:21 ----------

And why not to try a pair of rotating mirrors? This technique was used with gas lasers to generate "giant" pulses. The mirrors should rotate so that the laser operation is only possible when they are both in "normal-incidence" position. By adjusting their rotation rate, you can shorten the pulse down to nanoseconds.

A Kerr Cell - I knew there was something that could so it but couldn't remember. As you say, expensive though. I was also forgetting about the wavelength - a bit long for most techniques.

Keith

Thank you guys.

I have read more in the internet and it looks like the only way to switch on/off the laser beam is only possible by means of deflecting or modulating it with different types of electro-optic effects.

So, I am digging at that area right now.

Thank you again.

I think you would need to change over to a different type of laser, or add a Q switch to the CO2 laser tube. BY adding a Q switch, your power supply remains on, and the CO2 gas remains pumped, but the end mirror swaps from an oscillating to non oscillating condition--a much faster way of tuning the light on and off than by changing the power supply voltage.

At 20W, I would not fool around unless I really knew what I was doing!