I'm looking to make a proper red laser (not a flashlight like my 1.2W red laser turned out to be). I've heard good things about Sh@rp's 700mW diode divergence-wise, but I want to hear from you guys: which red laser diode offers the best divergence (sans FAC--can't afford that) whilst still offering some decent power?
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Which Diode has the best Divergence:Power Ratio?
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Wakrah
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Divergence is a yin-yang reality, it is the size of the diode emitter and the focal length of the collimation lens together which produce a given divergence, neither alone fix it to be what it will be. Due to this, the diode you already bought might be just what you need, if using a longer FL lens or beam expander:
So far, I have not seen a high power low divergence red laser diode, for that matter, any high to medium power single emitter laser diode (as laser diodes go) which produce low divergence without using larger diameter collimation lenses to make up for it. I understand you are looking for the best trade off of power to divergence, but I believe you likely won't find a diode which will suit what you want well enough, not at that wavelength, unless you don't mind a fat beam.
If you use a long focal length lens to collimate the beam from your laser diode, or a beam expander with your laser, the divergence can be fairly low, even for red (which unless a low power single mode diode, all red LD's have relatively high divergence). If I were looking for the highest power lowest divergence nicest looking laser beam from a diode at any wavelength or color, for a pointer I'd just go with the highest power single beam diode you can find and then if the divergence will be too high, decide on either a larger longer focal length collimation lens, or adding a beam expander on the output.
You can simply add a 10X beam expander to what you already have and end up with what you are looking for far easier than redesigning the whole pointer, but using a beam expander comes at a cost; reduced output. However, if using a quality beam expander with low loss AR coatings on the optics, the loss isn't so great as to make much difference, not a difference you will be able to see.
If you want to start over, or re-engineer the pointer, instead of using a beam expander, collimate the beam with a single large diameter long focal length lens and the output power will be a bit higher than you would have if first collimating the output with a smaller lens, and then putting a beam expander in front.
If you use a long enough focal length lens to collimate the output of the diode with (which will produce a larger diameter beam), for laser pointer use (not burning) it is fairly moot if the beam is corrected to be more square or not because if the beam is expanded enough (no need for a BE in this case with the added loss) both axis will diverge so much slower the beam will remain tight for as far as the eye can see, without turning into a sky rake, as is normal for all red laser diodes, unless a single mode diode and even they have too much of a rectangle for my taste.
Power for power, red is already a wavelength the eye is less sensitive too, although not so terrible at 638 nm compared to 650 or longer, but in either case to have a bright appearing beam you really need as much power as you can muster, which I believe is what you are wanting. Only thing is, if you use a long focal length lens to collimate the beam with, or a beam expander after collimation, you will have a fat beam, which at close range won't appear as bright, but in the far distance will remain as bright and not fade out nearly as fast as a thin high divergence beam would which spreads very quickly.
Note: If buying a beam expander, make sure the input lens diameter is large enough for the beam diameter you will be shooting into it, and that at whatever X factor the unit is, multiplying the input beam diameter does not overshoot the diameter of the beam expander output lens too. You need to find the actual specs, some beam expanders may have a 5 mm input lens but only allow a 1.5 mm diameter beam at the input without either being clipped at that input, or cut off at the output lens and result in a large loss of power. Also, make sure the lenses have AR coating and that the coating is for the red wavelength, in this case.
So far, I have not seen a high power low divergence red laser diode, for that matter, any high to medium power single emitter laser diode (as laser diodes go) which produce low divergence without using larger diameter collimation lenses to make up for it. I understand you are looking for the best trade off of power to divergence, but I believe you likely won't find a diode which will suit what you want well enough, not at that wavelength, unless you don't mind a fat beam.
If you use a long focal length lens to collimate the beam from your laser diode, or a beam expander with your laser, the divergence can be fairly low, even for red (which unless a low power single mode diode, all red LD's have relatively high divergence). If I were looking for the highest power lowest divergence nicest looking laser beam from a diode at any wavelength or color, for a pointer I'd just go with the highest power single beam diode you can find and then if the divergence will be too high, decide on either a larger longer focal length collimation lens, or adding a beam expander on the output.
You can simply add a 10X beam expander to what you already have and end up with what you are looking for far easier than redesigning the whole pointer, but using a beam expander comes at a cost; reduced output. However, if using a quality beam expander with low loss AR coatings on the optics, the loss isn't so great as to make much difference, not a difference you will be able to see.
If you want to start over, or re-engineer the pointer, instead of using a beam expander, collimate the beam with a single large diameter long focal length lens and the output power will be a bit higher than you would have if first collimating the output with a smaller lens, and then putting a beam expander in front.
If you use a long enough focal length lens to collimate the output of the diode with (which will produce a larger diameter beam), for laser pointer use (not burning) it is fairly moot if the beam is corrected to be more square or not because if the beam is expanded enough (no need for a BE in this case with the added loss) both axis will diverge so much slower the beam will remain tight for as far as the eye can see, without turning into a sky rake, as is normal for all red laser diodes, unless a single mode diode and even they have too much of a rectangle for my taste.
Power for power, red is already a wavelength the eye is less sensitive too, although not so terrible at 638 nm compared to 650 or longer, but in either case to have a bright appearing beam you really need as much power as you can muster, which I believe is what you are wanting. Only thing is, if you use a long focal length lens to collimate the beam with, or a beam expander after collimation, you will have a fat beam, which at close range won't appear as bright, but in the far distance will remain as bright and not fade out nearly as fast as a thin high divergence beam would which spreads very quickly.
Note: If buying a beam expander, make sure the input lens diameter is large enough for the beam diameter you will be shooting into it, and that at whatever X factor the unit is, multiplying the input beam diameter does not overshoot the diameter of the beam expander output lens too. You need to find the actual specs, some beam expanders may have a 5 mm input lens but only allow a 1.5 mm diameter beam at the input without either being clipped at that input, or cut off at the output lens and result in a large loss of power. Also, make sure the lenses have AR coating and that the coating is for the red wavelength, in this case.
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Wakrah
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Divide the focal length of the G8 by the FL of the G2, and the figure you get will be the multiple of the reduced amount of divergence. IMO not enough, did you see the thread I recently made in the optics section?
Build something like that with a shorter FL lens as the 15 mm diameter of my 30 mm FL lens is probably too small for a red diode at that FL, the beam will probably be too fat cutting a portion of it off inside the barrel. I could calculate the diameter for you at a given FL, I will work on that later, what is the diode you have? The Sharp GH0637AA2G diode? I have a pointer with that in it and was satisfied at 10 expansion beyond what a G2 lens provided, that would require a lens about one inch diameter, I think.
Edit: Edited out my full width estimate.
Build something like that with a shorter FL lens as the 15 mm diameter of my 30 mm FL lens is probably too small for a red diode at that FL, the beam will probably be too fat cutting a portion of it off inside the barrel. I could calculate the diameter for you at a given FL, I will work on that later, what is the diode you have? The Sharp GH0637AA2G diode? I have a pointer with that in it and was satisfied at 10 expansion beyond what a G2 lens provided, that would require a lens about one inch diameter, I think.
Edit: Edited out my full width estimate.
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For high power 638nm diodes, the Sharp 700mw unit is the best there is. For a given lens it has similar divergence to an M140, M462, NDB 7675 or NDB 7875. I used mine through a G7 lens and it was totally decent, still (as always) would be better through a single axis cylinder pair to correct the fast axis but it was totally acceptable through a G7. A G8 lens should be similar if not better. If divergence is important to you don't even think about using a G2 or similar short FL lens.
The Sharp 700 diode doesn't like to be overdriven. It simply won't get any brighter after about 800ma of current. On DTR's test his unit kept gaining output after 800ma (with poor efficiency) but mine would dim after 820ma. Even though the output kept increasing in DTR's test, it doesn't mean it was gaining brightness. The wavelength of these diodes increases dramatically when overdriven and the 630-660nm spectrum is extremely sensitive to wavelength for perceived brightness to our eyes. Moving from 638nm to 642nm takes quite a hit in brightness for the same power output.
Given the same lens, the Sharp 700 has about half the divergence of a Mits P73 or Oclaro 700, but twice the beam diameter. The latter is only important if you plan to use them for laser shows and need a small beam diameter to fit on your scanning mirror.
The Sharp 700 diode doesn't like to be overdriven. It simply won't get any brighter after about 800ma of current. On DTR's test his unit kept gaining output after 800ma (with poor efficiency) but mine would dim after 820ma. Even though the output kept increasing in DTR's test, it doesn't mean it was gaining brightness. The wavelength of these diodes increases dramatically when overdriven and the 630-660nm spectrum is extremely sensitive to wavelength for perceived brightness to our eyes. Moving from 638nm to 642nm takes quite a hit in brightness for the same power output.
Given the same lens, the Sharp 700 has about half the divergence of a Mits P73 or Oclaro 700, but twice the beam diameter. The latter is only important if you plan to use them for laser shows and need a small beam diameter to fit on your scanning mirror.
Wakrah
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I have the spec sheets on all three of these, the GH0637AA2G shows the uncollimated divergence figures at half intensity angle, not full. Note: I edited the following data sheets in after seeing the post following this one.
Oclaro specifies at full intensity angle:
Mitsubishi does not indicate if these specs are half or full intensity angle, my bet is since they don't say, it is half.
Sharp specifies at Half Intensity Angle:
At full width, the raw divergence works out to 36 and 70 degrees, huge.
Oclaro specifies at full intensity angle:
Mitsubishi does not indicate if these specs are half or full intensity angle, my bet is since they don't say, it is half.
Sharp specifies at Half Intensity Angle:
At full width, the raw divergence works out to 36 and 70 degrees, huge.
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Aren't all diodes spec'd at half intensity angle? Regardless, if you put a Sharp and a Mits side by side with the same lens, you will find that the Sharp linewidth has half the divergence of the Mits.
Wakrah
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The full width at half maximum (FWHM) is the width of a line shape at half of its maximum amplitude, as shown below:
A closely related quantity is the half width at half maximum (HWHM) or the Resolving Resolution and it is half of the FWHM. For Gaussian line shapes, the FWHM is about 2.4 standard deviations. While the concept is simple, this is a vital quantity; the FWHM is used to define resolution. If two peaks have overlapping FWHMs, they are unresolvable, i.e. they will look like one peak.
Spec sheets for the three diodes you mentioned: https://imageevent.com/qdf_files/te...vecommunications/redlaserdiodes?rotp=7836&n=0
When I see a diode specified at half-width, to me that is too misleading for many as it doesn't give the full size of the beam diameter. The Sharp diode is specified at half. In my scrutinizing view there is a reason they show half width, it makes the specifications appear better to the casual glance, maybe specifying the beam diameter that way is fine if you are masking the beam, but how many of us do that?
A closely related quantity is the half width at half maximum (HWHM) or the Resolving Resolution and it is half of the FWHM. For Gaussian line shapes, the FWHM is about 2.4 standard deviations. While the concept is simple, this is a vital quantity; the FWHM is used to define resolution. If two peaks have overlapping FWHMs, they are unresolvable, i.e. they will look like one peak.
Spec sheets for the three diodes you mentioned: https://imageevent.com/qdf_files/te...vecommunications/redlaserdiodes?rotp=7836&n=0
When I see a diode specified at half-width, to me that is too misleading for many as it doesn't give the full size of the beam diameter. The Sharp diode is specified at half. In my scrutinizing view there is a reason they show half width, it makes the specifications appear better to the casual glance, maybe specifying the beam diameter that way is fine if you are masking the beam, but how many of us do that?
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Actually Oclaro specifies half intensity angle. FWHM means Full Width Half Maximum, the same as the Mits, the same as the Sharp. I don't know what you're going on about.I have the spec sheets on all three of these, the GH0637AA2G shows the uncollimated divergence figures at half intensity angle, not full. Note: I edited the following data sheets in after seeing the post following this one.
Oclaro specifies at full intensity angle:
Mitsubishi does not indicate if these specs are half or full intensity angle, my bet is since they don't say, it is half.
Sharp specifies at Half Intensity Angle:
Wakrah
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The Sharp diode is not the best choice for a given lens diameter, but that becomes moot if using a longer FL lens. He said the beam output was too wide, in so many words, just use a longer FL lens, but for multimode red, I don't believe the G8 is sufficient, not a long enough FL for what I prefer and believe he might also like, but I'd try the G8 and see, no reason to spend money on something more until he tries it.
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Dude, he asked a simple question. Which high power red diode has the best divergence? It's the Sharp, by a factor of nearly two, for a given lens. What's your deal?The Sharp diode is not the best choice for a given lens diameter, but that becomes moot if using a longer FL lens. He said the beam output was too wide, in so many words, just use a longer FL lens, but for multimode red, I don't believe the G8 is sufficient, not a long enough FL for what I prefer and believe he might also like, but I'd try the G8 and see, no reason to spend money on something more until he tries it.
Wakrah
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I ordered the diode from DTR, I will check it myself. I disagree with your assessment.
After I finish my IR build I might give red another shot, to me it seems that I might be happier just sticking with one of the weak single mode reds (which I can easily salvage from a DVD burner) since they'd probably offer the best divergence and wind up having a brighter beam than even my 1.2W red after about 10 feet or so lol
I don't like flashlights!
I don't like flashlights!
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You can get a really nice, tight beam from some of those DVD burners. Look for a LPC-826 or an LPC-840 (or any open can diode, looks like a P73 mits) and with a decent lens the spot looks extremely bright when driven at 350mA.. heck, even the 3.8mm open can diodes out of laptop DVD burners can be run at 300mA and are super bright with a pencil lead thin beam.
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Wakrah
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Those are single mode diodes, the divergence isn't too bad with a 6.3 mm diameter lens, but I still like to use a longer focal length lens than the G2 with them too. Typical divergence prior to collimation is a bit more than 10 and 15 degrees, there is no data sheet to be found for that diode either, except maybe this is good info:
The divergence of single mode diodes of any VIS color are less than multimode diodes due to their much smaller emitter aperture and waveguide operation, although for red, the divergence will typically be higher than blue or violet, due to the longer wavelength.
The divergence of single mode diodes of any VIS color are less than multimode diodes due to their much smaller emitter aperture and waveguide operation, although for red, the divergence will typically be higher than blue or violet, due to the longer wavelength.
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Don't take my word for it.... https://www.photonlexicon.com/forums/showthread.php/26594-Sharp-700mW-638-Diode-Quick-Test
"I tested it against a P73 diode. At first I got really excited because the spot was just a bit over half the size of the P73! However, the aperture size is much larger."
"Even though the far field is half the size, the nearfield is about 2X the area"
So.. quoting myself now.. "Which high power red diode has the best divergence? It's the Sharp, by a factor of nearly two, for a given lens. "
