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Well, I've noticed that we keep seeing the same questions about DPSS (mostly green) lasers over and over again, so I'm starting this thread to post permanent answers to some of them..
The first thing I'll do is link to the section of Sam's Laser FAQ dealing with DPSS lasers: Sam's Laser FAQ - Solid State Lasers
This link contains the answers to just about any questions regarding DPSS lasers.
If you're still wondering after reading that section of Sam's then here are some common FAQs:
[highlight]Q: Why does my green DPSS laser seem dimmer/brighter at first and then change power gradually over the first few minutes of use?[/highlight]
A: DPSS lasers are much more complex than diode lasers like DVD burner diodes or blu-ray diodes. Because of this, a warmup period is required for the internal parts of the laser to reach a stable temperature (most manufacturers state a warm-up of 5-15 min.). While this warm-up is occurring, the power output and beam undergo large fluctuations, but as the warm-up progresses they become more and more stable until it finally reaches the optimum temperature for operation. This is normal with all DPSS lasers and is not a defect.
[highlight]Q: What is the optimum temperature for my DPSS laser to operate at?[/highlight]
A: It varies from laser to laser since no two DPSS lasers are perfectly identical. The reason that there is an optimum temperature for stable operation is that as the pump diode inside the laser heats up and the rest of the laser heats up around it, the internal alignment changes due to expansion from the heat. These subtle changes are what cause instability. At some point during these changes an optimum alignment is achieved. At this point the laser is at it's peak intensity. Going much above or below this point will alter the intensity and sometimes the beam shape of the output. How much depends on the individual laser and no two are exactly alike.
A good rule of thumb to avoid damaging the laser is to not allow the case temperature to exceed 50C. *Also, being too cold will cause a sharp decrease in output and if it is extremely cold the laser may not work at all. Most typical green laser pointers do not have adequate heatsinking for the laser inside, and so their output may never be entirely stable. Lab-style DPSS lasers typically have several features (thermal and optical control devices) built in to ensure long-term output stability. Due to cost and space constraints, these features are left out of DPSS laser pointers, resulting in a comparative lack of stability..
[highlight]Q: Why does the beam from my DPSS laser seem to change brightness and shape randomly?[/highlight]
A: What you are witnessing is a phenomenon called mode-hopping. Describing why this happens is extremely complicated (more info can be found here: http://laserpointerforums.com/f44/some-facts-about-mode-hopping-28456.html).
Mode-hopping that occurs during the warmup phase, during operation above/below optimum temperature, or during operation while powered by an unstable source like low batteries is not the result of a defect. Mode-hopping that occurs randomly seemingly for no reason at all is the result of misalignment of the internal parts of the laser and is considered a defect. Ideally a TEM00 beam is most desirable. This is a beam with a single spot, brighter in the center than the edges, also known as "perfect gaussian power distribution"
[highlight]Q: Why, after my DPSS laser suddenly stopped working, do I see just a dim red light coming from the aperture?[/highlight]
A: DO NOT LOOK INTO THE APERTURE!!!!!!! This dim red light is actually being produced by an extremely powerful infrared laser. Since IR light is invisible, all we can see is the dim red light. Don't be fooled by the dimness, even in a 5mW DPSS laser the IR output is guaranteed to be at least 200mW, which is more than enough to fry your eyes. The reason that you can see this is because some of the internal parts of the laser have gone out of alignment..
[highlight]Q: How do I refocus my green laser pointer?[/highlight]
A: Focusing commercially made green modules/pointers can be extremely difficult. The lens assembly usually requires a spanner wrench to turn it without scratching the lens, and is usually glued in place. With green pointers in most cases the beam diameter exiting the aperture is narrow enough to permit burning, so truthfully I don't recommend attempting to refocus them to burn things. If you're not happy with the divergence of your laser, you can try to refocus to correct this. Once you have broken the glue bond and loosened the lens assembly enough to turn it, then refocus it using this calculator to obtain the desired divergence value: pseudonomen137's JScript mRad Calculator
By measuring the beam diameter at the aperture and again at a given distance, you can calculate the divergence in mRad.
These are just some of the top questions that I see asked here frequently.. I encourage anyone to add to this with other questions and/or answers they may have or may have seen..
The first thing I'll do is link to the section of Sam's Laser FAQ dealing with DPSS lasers: Sam's Laser FAQ - Solid State Lasers
This link contains the answers to just about any questions regarding DPSS lasers.
If you're still wondering after reading that section of Sam's then here are some common FAQs:
[highlight]Q: Why does my green DPSS laser seem dimmer/brighter at first and then change power gradually over the first few minutes of use?[/highlight]
A: DPSS lasers are much more complex than diode lasers like DVD burner diodes or blu-ray diodes. Because of this, a warmup period is required for the internal parts of the laser to reach a stable temperature (most manufacturers state a warm-up of 5-15 min.). While this warm-up is occurring, the power output and beam undergo large fluctuations, but as the warm-up progresses they become more and more stable until it finally reaches the optimum temperature for operation. This is normal with all DPSS lasers and is not a defect.
[highlight]Q: What is the optimum temperature for my DPSS laser to operate at?[/highlight]
A: It varies from laser to laser since no two DPSS lasers are perfectly identical. The reason that there is an optimum temperature for stable operation is that as the pump diode inside the laser heats up and the rest of the laser heats up around it, the internal alignment changes due to expansion from the heat. These subtle changes are what cause instability. At some point during these changes an optimum alignment is achieved. At this point the laser is at it's peak intensity. Going much above or below this point will alter the intensity and sometimes the beam shape of the output. How much depends on the individual laser and no two are exactly alike.
A good rule of thumb to avoid damaging the laser is to not allow the case temperature to exceed 50C. *Also, being too cold will cause a sharp decrease in output and if it is extremely cold the laser may not work at all. Most typical green laser pointers do not have adequate heatsinking for the laser inside, and so their output may never be entirely stable. Lab-style DPSS lasers typically have several features (thermal and optical control devices) built in to ensure long-term output stability. Due to cost and space constraints, these features are left out of DPSS laser pointers, resulting in a comparative lack of stability..
[highlight]Q: Why does the beam from my DPSS laser seem to change brightness and shape randomly?[/highlight]
A: What you are witnessing is a phenomenon called mode-hopping. Describing why this happens is extremely complicated (more info can be found here: http://laserpointerforums.com/f44/some-facts-about-mode-hopping-28456.html).
Mode-hopping that occurs during the warmup phase, during operation above/below optimum temperature, or during operation while powered by an unstable source like low batteries is not the result of a defect. Mode-hopping that occurs randomly seemingly for no reason at all is the result of misalignment of the internal parts of the laser and is considered a defect. Ideally a TEM00 beam is most desirable. This is a beam with a single spot, brighter in the center than the edges, also known as "perfect gaussian power distribution"
[highlight]Q: Why, after my DPSS laser suddenly stopped working, do I see just a dim red light coming from the aperture?[/highlight]
A: DO NOT LOOK INTO THE APERTURE!!!!!!! This dim red light is actually being produced by an extremely powerful infrared laser. Since IR light is invisible, all we can see is the dim red light. Don't be fooled by the dimness, even in a 5mW DPSS laser the IR output is guaranteed to be at least 200mW, which is more than enough to fry your eyes. The reason that you can see this is because some of the internal parts of the laser have gone out of alignment..
[highlight]Q: How do I refocus my green laser pointer?[/highlight]
A: Focusing commercially made green modules/pointers can be extremely difficult. The lens assembly usually requires a spanner wrench to turn it without scratching the lens, and is usually glued in place. With green pointers in most cases the beam diameter exiting the aperture is narrow enough to permit burning, so truthfully I don't recommend attempting to refocus them to burn things. If you're not happy with the divergence of your laser, you can try to refocus to correct this. Once you have broken the glue bond and loosened the lens assembly enough to turn it, then refocus it using this calculator to obtain the desired divergence value: pseudonomen137's JScript mRad Calculator
By measuring the beam diameter at the aperture and again at a given distance, you can calculate the divergence in mRad.
These are just some of the top questions that I see asked here frequently.. I encourage anyone to add to this with other questions and/or answers they may have or may have seen..
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