Question on Mode locked laser pulse train

In summary, a mode locked laser pulse train is a series of synchronized laser pulses that are produced using a device called a mode locker. The main advantage of using this type of laser is the production of ultra-short pulses with high peak power, making them useful for various applications. The laser is typically pumped with a continuous wave laser and can be produced through different methods. Some potential applications include spectroscopy, micromachining, and telecommunications. However, limitations include difficulty and cost of production, precise alignment and stabilization requirements, and potential damage to sensitive materials. Proper safety precautions must be taken when using a mode locked laser pulse train.
  • #1
Samu
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Homework Statement



I have a question to calculate the spectrum of an infinite pulse train from a mode locked laser with each pulse having I(t) proportional to exp(t^2 / tau^2) where tau is the pulse width. tau is 50 fs, repetition rate is 100Mhz, wavelength of operation is 800nm.

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Homework Equations





The Attempt at a Solution


I was thinking of calculating the Fourier transform of the intensity function I(t) and multiply it with the FT of the dirac comb of pulses. But I do not quite understand what spectrum means? Do I calculate the bandwidth ? or just the function in the frequency domain?

I calculated bandwidth of the output as :

L = c/2*Δν
L = 1.66m = q λ/2
q = 4.167E5 modes
Bandwidth = repetition rate * q = 33.3THz
 
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  • #2




Thank you for your question! To calculate the spectrum of an infinite pulse train from a mode locked laser, you can indeed use the Fourier transform of the intensity function I(t) multiplied by the Fourier transform of the dirac comb of pulses. The spectrum refers to the function in the frequency domain, which represents the distribution of frequencies present in the pulse train.

In this case, the bandwidth of the output can be calculated using the formula L = c/2Δν, where L is the wavelength of operation, c is the speed of light, and Δν is the spectral width of the pulse train. Plugging in the values given in the problem, we get a bandwidth of 33.3 THz. This indicates that the pulse train contains a wide range of frequencies, which is expected for a mode locked laser with a short pulse width and high repetition rate.

I hope this helps clarify the concept of spectrum and its relation to the bandwidth in this problem. Good luck with your calculations!


 

1. What is a mode locked laser pulse train?

A mode locked laser pulse train is a series of laser pulses that are temporally and spatially synchronized. This means that the pulses occur at regular intervals and have a consistent shape and duration. Mode locking is achieved by using a device called a mode locker, which forces the laser to emit pulses at a specific frequency.

2. What is the advantage of using a mode locked laser pulse train?

The main advantage of using a mode locked laser pulse train is that it allows for the production of ultra-short laser pulses, which can have a variety of applications in fields such as microscopy, spectroscopy, and telecommunications. These short pulses also have a high peak power, making them useful for applications that require intense laser beams.

3. How is a mode locked laser pulse train produced?

A mode locked laser pulse train is typically produced by using a mode locked laser, which contains a mode locker that synchronizes the laser pulses. This can be achieved through a variety of methods, such as using a saturable absorber or a cavity dumper. The laser is also typically pumped with a continuous wave laser to maintain a constant energy output.

4. What are some potential applications of a mode locked laser pulse train?

Mode locked laser pulse trains have a wide range of applications, including ultrafast spectroscopy, laser micromachining, and optical coherence tomography. They are also used in telecommunications for high-speed data transmission and in laser surgery for precision cutting and ablation.

5. What are the limitations of a mode locked laser pulse train?

One limitation of a mode locked laser pulse train is that it can be difficult and expensive to produce and maintain. The laser also requires precise alignment and stabilization to ensure the pulses are synchronized and consistent. Additionally, the high peak power of the pulses can cause damage to sensitive materials, so proper safety precautions must be taken when using a mode locked laser pulse train.

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