# Laser characterization.

1. Nov 6, 2011

### vivek.iitd

What does the following statement tells about the laser output, i can understand the literal meaning but what does it tell about the power levels, temporal profile etc.?

"the pump laser delivers 500-μJ pulses at 1.064 μm with a 12.5-kHz repetition rate"

2. Nov 6, 2011

### Staff: Mentor

You can find the power output by multiplying the pulses per second by the energy per pulse. I don't know exactly what you mean by "temporal profile" though.

Last edited: Nov 6, 2011
3. Nov 6, 2011

### vivek.iitd

Thank you for your reply, as you said multiplying Energy per pulse and repetition rate will give me Average power. And if i have pulse duration = 20ns, then Pulse energy*pulse duration will give me Peak power right?

By temporal profile i mean, as this is a pulsed laser, so how the power of a pulse will vary as a function of time. If we consider it to be a Gaussian, then we can write it like

P = Po*exp(-(t/T)^2) where Po is the peak power as calculated above and T is FWHM.

Am i right?

4. Nov 6, 2011

### Staff: Mentor

I think it depends on if the 500 microjoules is an "average" or not. If you apply 100 joules for the first and last 10% of the pulse, but 700 joules for the rest, your peak power will not be the same as it would be if it is a steady 500 for the entire pulse.

I'm not sure honestly, but I don't think there's enough information to figure out the temporal profile. But you could assume a profile if you want to. Someone else will have to look at the equations though, I'm not familiar with them.

5. Nov 6, 2011

Thanks.

6. Nov 6, 2011

### Redbelly98

Staff Emeritus
Almost. To calculate Po, you need to set the integral of that expression equal to the pulse energy, 500 uJ.

7. Nov 6, 2011

### vivek.iitd

okay thank you.

8. Nov 6, 2011

### Claude Bile

Er, hold on;

Think about this for a moment. This suggests that the longer the pulse duration, the higher the peak power. Clearly this is not correct. Instead it is the shorter the pulse duration the higher the pulse energy.

If in doubt, consider the units involved. Power = Energy/time.

Also, you cannot calculate the temporal profile with the information given in the original post. We can calculate some integrals, but that is about it. One would need to use a fast detector and an oscilloscope to measure the intensity profile of such a laser as a function of time.

Claude.

9. Nov 6, 2011

### vivek.iitd

ohh sorry, yes it should be Power=Energy per pulse/Pulse duration.

10. Nov 6, 2011