Power Spectral Density of a laser

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Discussion Overview

The discussion revolves around the concept of Power Spectral Density (PSD) in relation to laser error signals. Participants explore the relationship between PSD and Fourier Transform (FT), the significance of PSD in analyzing noise in lasers, and seek references for further reading on the topic.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested

Main Points Raised

  • Some participants propose that the PSD provides information about the average distribution of power in a frequency band, which differs from the FT.
  • One participant mentions that the PSD can be viewed as the Fourier Transform of the autocorrelation function of the signal.
  • Another participant notes that understanding the theory behind PSD may not be necessary for practical applications, unless one needs to consider the effects of different window functions on the spectrum.
  • Participants discuss the scarcity of literature on noise in diode lasers and related topics, expressing interest in finding good references.
  • One participant suggests a resource by Enrico Rubiola, indicating its relevance to stabilized lasers and oscillators.

Areas of Agreement / Disagreement

There is no consensus on the relationship between PSD and FT, as participants provide differing perspectives on their definitions and implications. The discussion remains unresolved regarding the depth of theoretical understanding required for practical use of PSD.

Contextual Notes

Participants express uncertainty about the literature available on the topic, indicating a potential gap in accessible resources related to noise in diode lasers and PSD.

Who May Find This Useful

Individuals interested in the analysis of laser systems, particularly in the context of noise and spectral analysis, may find this discussion relevant.

Niles
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Hi

I am confused about the concept of Power Spectral Density (PSD) of a laser. Say I hook up my laser error signal to a PSD: Is it correct to say that the PSD basically gives me the Fourier transform of the signal?


Niles.
 
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As a general statement a power spectrum is the Fourier Transform of a signal. I am not familiar with your context.
 
Niles said:
Hi

I am confused about the concept of Power Spectral Density (PSD) of a laser. Say I hook up my laser error signal to a PSD: Is it correct to say that the PSD basically gives me the Fourier transform of the signal?Niles.

Sort of. The PSD gives you slightly different information than the FT; if you plot the PSD you are showing the (average) distribution of POWER in the frequency band.
So it is slightly different than a FT.

Most spectrum analysers can show both the FFT and the PSD.

In your context the PSD is important for several reasons, not least because it allows you to figure out which type of noise dominates for a certain frequency (=what the controller is having to compensate for); this can be seen by looking at the slope of the PSD.
 
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Not my field but isn't the PSD the FT of the autocorrelation function of the signal?
 
DrDu said:
Not my field but isn't the PSD the FT of the autocorrelation function of the signal?

Yes, it is.
 
Indeed

At work I use a book called "Spectral Analysis of Signals" by Stoica as a reference book.

http://www.amazon.com/dp/0131139568/?tag=pfamazon01-20

However, you don't really need to understand all the theory to use a PSD (unless you need to understand how e.g. different window functions will affect the shape of the spectrum). PSDs are extremely common in some fields, and when people talk about spectrum it is frequently the PSD (and not the FT) they are talking about.
 
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Thanks for all your help. Generally it seems to me that the litterature on noise in diode lasers, PSDs, drift, etc.. is sparse. If you know of any good references, I would be very interested.

Best wishes,
Niles.
 
Have a look at Enrico Rubiola's homepage

http://rubiola.org/

His stuff is mainly related to oscillators, but much of the material will be relevant to e.g. stabilized lasers as well.
He once sent me a reference to a book dealing specifically with lasers, I will try to find the reference when I'm back at work next week,
 
f95toli said:
Have a look at Enrico Rubiola's homepage

http://rubiola.org/

His stuff is mainly related to oscillators, but much of the material will be relevant to e.g. stabilized lasers as well.
He once sent me a reference to a book dealing specifically with lasers, I will try to find the reference when I'm back at work next week,

Thanks, I would be very interested in that.

Best wishes,
Niles.
 

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