Hi! The simplest thing to do is to use a variable attenuator. You can build your own variable attenuator using a half-wave plate and a polarizer. Then you can vary the power without even touching the laser

Hi, I agree with the method of Fabien Bretenaker.

Not to change all experimental parameters at once, the half-waveplate with polarizer (or variable neutral density filter) is the most robust solution that requires no additional alignment.

Also, if you are working with the pulses shorter than 50-60 fs, be sure use appropriate "ultrafast" optics (to avoid GVD), if you care about the pulse duration.

Normally, 80 MHz passively mode-locked laser systems are tunable within the certain wavelength range (depends on the pulse duration, which is linked to its spectrum). In this case, you can change the fluence by changing the carrier wavelength in the laser software.

It all depends on what do you mean by keeping the other parameters constant. The half-wave plate polarizer combination changes pulse energy, and hence peak power. Changing the beam cross-section by focusing changes fluence while keeping peak power constant. Which is best? It depends what do you want

Hi Muhammad,

fluence is the energy density typically measured in J/cm2 (Joule per square centimeter).

So if you want to tune it, you have to change either the pulse energy, or the beam size.

I guess you can only decrease it playing with the energy (with the help of some attenuator, as people suggest, or some filters). But you can also both increase or decrease the fluence by changing the beam cross section (respectively focusing or defocusing your beam).

Best, AT

Hi,

The simplest way is to move sample out of focal plane but there are limitations. It would be interesting to determine them here together.

When you increase beam diameter you eventually reach the point where the energy is not absorbed at the beam border or its absorption cause only heating instead of ablation.

I would say that moving in the range of beam diameter up to ~60 um is in most cases reasonable. Off course it depend on pulse energy and material used.

Greetings,

Bogusz

Hi,

the question is weather you want to keep pulse duration constant (which results in peak power). So regarding to this you need to be aware of pulse compensation if you use any transmissive optic in the beam path.