# Laser Pulse Duration @ 2.5kHz FWHM

• bhartish
In summary, based on the provided data, it is not possible to calculate the pulse duration using just the pulse repetition frequency. The most reliable way is to measure the pulse width.
bhartish
I have pulse frequency as 2.5kHz. How to calculate laser pulse duration at FWHM (full width half maximum)

Having only the pulse repetition frequency is not sufficient to find the pulse duration.

bhartish said:
I have pulse frequency as 2.5kHz. How to calculate laser pulse duration at FWHM (full width half maximum)

The pulse repetition rate and the pulse duration do not correlate, generally speaking. Base on the provided data one can say only that the pulse duration is less than 400 microsec :-) . The most reliable way is measurement of the pulse width by fast enough photodiode and oscilloscope. If the duration is less than dosens of picoseconds other devices are used. If you do not need high presicion you can estimate the pulsewidth taking into consideration the other laser parameters. The most important are: type of the laser, resonator length, pulse energy (or the average power), and the beam spot diameter.

Yes I have average power = 300W, beam spot diameter = 0.37mm, I am using Co2 laser Now can we find?

bhartish said:
Yes I have average power = 300W, beam spot diameter = 0.37mm, I am using Co2 laser Now can we find?
Still no.

You can get the energy per pulse -- using the joules/sec and pulses/sec values you have. From there you could get the pulse width if you knew the peak power within a pulse.

Are you actually in a lab using an actual laser? Is there a spec sheet for the laser?

Yes I am in lab and I have used 750W peak power laser . I have specification sheet. But I don know peak power per pulse.

I have actually used three parameters in my experiment : Laser power (in terms of duty cycle), pulse frequency and scanning speed.

A neat way of measuring the pulse duration would be to use a fast rotating mirror and look at the duty cycle of the dashed line that would be projected on a distant screen. This method would eliminate the problem of the limitations of frequency response of any detector you were using. If you sync the rotation of the mirrir, you should get a stable pattern on the screen.

It's not quite whether you have both peak and mean power information on your spec sheet. If you did have, then the duty cycle would be in the order of
(mean power) / (peak power) - depending on the profile of the pulse, of course.

bhartish said:
Yes I have average power = 300W, beam spot diameter = 0.37mm, I am using Co2 laser Now can we find?

Writing "type of the laser" I had in mind not only type of the active medium but also the mode of operation? i.e. free running or Q-switched or mode locking. I'm not familiar with gas lasers but I have asked one of my friend who worked with them. He answered typical pulse duration depended on type of ionizaton of the gas. Photo-ionized lasers produce typically 1 microsec pulse plus about 20 mus of bottom. Electro-ionized lasers provide 20 mus and more. There may be other variants as well.

I suppose 0.37 mm is the beamspot after focusing rather than behind the laser output coupler.

bhartish said:
Yes I am in lab and I have used 750W peak power laser . I have specification sheet. But I don know peak power per pulse.

I have actually used three parameters in my experiment : Laser power (in terms of duty cycle), pulse frequency and scanning speed.

I don't understand - if the average power is 300 W while the peak one is 750 W, it should mean the pulse duration is about 400/2.5 mus. Am I wrong?

That would work if the pulse were 'flat topped'.

AlexLAV said:
I don't understand - if the average power is 300 W while the peak one is 750 W, it should mean the pulse duration is about 400/2.5 mus. Am I wrong?
Sounds reasonable to me, at least for a ballpark value. Though the 750 W is from the spec sheet, not an actual measurement of the laser being used. And I'm not sure if the 300 W figure is from specs or a measurement.
sophiecentaur said:
That would work if the pulse were 'flat topped'.
But it should at least give a reasonable estimate. For Gaussian-shaped pulses, it gives a value that is 26% too low.

So we estimate the pulse width to be 150-200 μs. Anybody know if there are detectors this fast at 10.6 μm wavelengths?

So if the pulse is 400 microseconds, 400 x 10-6
and speed of light is 3 x 108meters/second
Then the length segment of the laser pulse is only 120,000 meters

Last edited:
morrobay said:
So if the pulse is 400 microseconds, 400 x 10-6
and speed of light is 3 x 108meters/second
Then the length segment of the laser pulse is only 120,000 meters
Okay, but the pulse duration is not 400 μsec. That is what the OP would like to find out.

## 1. What does "Laser Pulse Duration @ 2.5kHz FWHM" mean?

Laser pulse duration refers to the length of time that a laser beam is active. It is typically measured in milliseconds (ms) or nanoseconds (ns). The notation "2.5kHz FWHM" indicates that the laser operates at a frequency of 2.5 kilohertz (kHz) and the pulse duration is measured at the full width at half maximum (FWHM) intensity level.

## 2. Why is laser pulse duration important?

The pulse duration of a laser can impact its effectiveness in various applications. For example, in medical procedures, a shorter pulse duration can minimize damage to surrounding tissue. In material processing, a longer pulse duration may be necessary for deeper cuts or engraving. It is important to consider the desired outcome when selecting a laser with a specific pulse duration.

## 3. How is laser pulse duration measured?

The pulse duration can be measured using various methods, such as photoelectric detectors or autocorrelators. These devices measure the intensity of the laser beam over time, allowing for the determination of its pulse duration. The FWHM method, mentioned in the notation, is a common way to measure the duration of a pulsed laser.

## 4. Can laser pulse duration be adjusted?

Yes, the pulse duration of a laser can be adjusted through various means, such as changing the optical cavity length or using modulators. This allows for fine-tuning of the laser for specific applications. However, the minimum and maximum achievable pulse durations may be limited by the laser's design and components.

## 5. How does laser pulse duration affect laser performance?

The pulse duration of a laser can impact its performance in terms of precision, accuracy, and efficiency. A shorter pulse duration can result in higher precision and accuracy, while a longer pulse duration may be necessary for certain processing tasks. Additionally, a shorter pulse duration can lead to more efficient use of the laser's energy, resulting in cost savings and longer-lasting components.

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