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muRRat
Wicked Lasers Master
Joined: 07 Dec 2006
Posts: 888
Picture(s): 110
Movie(s): 21
Location: TURKEY
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 Posted: 2/03/08, 10:08 AM Post subject: What is a |
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Here I found a very good explanation about pulsed lasers.
What is it and how is it made?
http://www.bbc.co.uk/dna/h2g2/A897609
This article can be a sticky!  |
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myslinky
Fusion Laser
Joined: 01 Jan 2008
Posts: 269
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| Posted: 4/23/08, 1:15 AM Post subject: |
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very good find muRRat, thank you! 
Do you have any pulsed lasers of your own? |
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Murudai
Phoenix Laser
Joined: 18 Apr 2008
Posts: 79
Movie(s): 1
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| Posted: 4/23/08, 3:13 AM Post subject: |
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Interesting article.
Would a pulsed laser be better at burning than a continuous one? I mean, the continuous one can put in more energy, but the big bursts of energy the pulsed one could do have got to count for something. |
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Hanneman
4.99mW Green Laser Toy
Joined: 02 Jun 2008
Posts: 7
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| Posted: 6/05/08, 12:53 AM Post subject: |
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That is a good article - both concise and accurate.
| Murudai wrote: |
Would a pulsed laser be better at burning than a continuous one? I mean, the continuous one can put in more energy, but the big bursts of energy the pulsed one could do have got to count for something. |
Yes, the pulsed laser would be better at burning, which is why it is used for abalation and laser machining. CW lasers don't cut as well and have the tendency to heat the area surrounding the cut, which can cause unwanted melting or destruction of the material.
Even though a pulsed laser and CW laser can have the same rated power (usually measured in Watts or J/s), low repetition rate pulsed lasers can dispense more instantaneous energy over a short time interval - similar to an impulse function. For example, if a NdYAG has 30 mJ pulses at a 20 Hz repetition rate, that would be equivalent to 600 mW of power (one definition). However, if the pulse width is 5 ns, each pulse equates to 6 MW of power (the other definition of power). I guess you could use the analogy of mining rock. You're more likely to break the rock by swinging a pick axe versus pressing the axe against the rock with the same amount of energy over a longer period of time.
The reason for this behavior is based on the difference in which CW and pulsed lasers operate. In both cases, in order for stimulated emission (or lasing) to occur, a population inversion must exist - more than 50% of the atoms/molecules/collective ensemble in the gain medium must be in the metastable excited state. So, for a CW laser, the rate of pumping must match the rate of lasing while maintaining the population inversion so that lasing can occur continuously. A [low rep rate] pulsed laser has an optical switch for resonance in the cavity, like a Q-Switch. First, the cavity is made non-resonant while the gain medium is pumped, usually well above the population inversion point. Then, the optical switch is opened so the cavity resonates (or rings like a bell) and lasing occurs. The pulse will self-terminate when population inversion no longer exists. The increased power comes from an increased amount of energy stored in the cavity, and the avalanche of light energy as it is released from the cavity.
The high repetition rate (MHz) pulsed or quasi-CW lasers fall somewhere between the 2 extremes above. |
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