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Which one should i buy?

Koff

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PL 405/445nm 500-2000mW from laserbtb or SF501B 445nm Blue from sci-fi lasers?
Which is better?
 





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I also recommend the one from Sci-Fi lasers, they are made by one person one at a time as the orders come in, it's a simpler design less likely to break and made from standard parts. Laserbtb are considered good though, the host has extra features built in and it's factory made in China (less quality control). Most people are satisfied with what they get from Laserbtb, they are safe to buy from. What country are you in? One ships from China, the other ships from Israel, both can take awhile before you get it.

Alan
 
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Keep in mind for equal power outputs 445nm blue is only 10 percent as bright to the human eye as 532nm green is, 405nm violet-blue is only 1 percent as bright compared to green 532nm.

If you compare 445nm blue to 520nm green the percentages are closer together due to 520nm being less brilliant than 532nm at the same powers, here are some price and brilliance comparisons for 520nm green:

1.6 watt 445nm diode: ~43 dollars (~2.7 cents per milliwatt) from https://sites.google.com/site/dtrlpf/home/diodes/osram-pltb450-1-4w-450nm

1 watt 520nm diode: ~370 dollars (37 cents per milliwatt) from https://sites.google.com/site/dtrlpf/home/diodes/ndg-1w-520nm (can sometimes produce over 1.5 watts output @ <25 cents per milliwatt). If you get a high efficiency 520nm laser diode which can produce 1.5 watts output, the cost of the blue vs green diodes relative to the perceived brilliance they can produce isn't too far off from being about the same and with the price of 520nm laser diodes coming down faster than the blue diodes, I expect green laser diodes will eventually be less expensive than blue 445nm in terms of perceived brightness.

Left side for beam
updarte%20520%20vs%20455nm%201500%201600_zpsx4e1n63n.jpg
2nd_zpsxscvt2ed.jpg
Right side for dot​

The above beam and dot comparisons assume the 1 watt 520nm diode can be driven to produce 1.5 watts output, if it only produces 1 watt of green here's the brightness comparision, below:

last_zps3n62sq9z.jpg
520nm1watt%20dot_zps57ohusin.jpg

If you had an eight watt 455nm laser it would have close to the same beam brightness to the human eye as a 1 watt 520nm laser, but you would need close to 12 watts of 455nm blue to look as bright as a 1.5 watt 520nm green laser beam. You won't be buying a 12 watt output 455nm laser diode, they don't exist that I have seen yet.

If you buy one of those 8 dollar 532nm green 50-100 mw laser pointers from China, the cost vs perceived brightness is hugely on the side of green being the least expensive for the visual bang and that's not even factoring in they are already built with a complete host, driver, lens and all, just add batteries and play :) http://www.ebay.com/itm/5miles-532n...power-powerful-8000M-pointer-EC-/221658152202 (luck of the draw for what you get on these, they can be anywhere from 40 to 100 mw, usually about 60mw, 25% of that IR mixed in with the green output). If you are considering a 405nm violet-blue take a look at the right most brightness comparison graphics below, they are hardly visible to the human eye compared to green.

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One gotcha with the higher power multimode 520nm lasers, unless a beam expander is used with them, their divergence is far greater than just about any cheap or expensive 532nm DPSS laser. I'd never have a multimode 520nm laser pointer without at least a 3X beam expander on it myself to bring their divergence down to normal. If you had a ~3 mRad divergence multimode laser (not unusual) and expanded it by a factor of 3X the divergence would be reduced to about 1 mRad which is better than most 532nm DPSS lasers and the thickness of the beam only increased by a factor of three times wider. Although if you took that same 3 mRad multimode laser and put a 10X beam expander on it, then you would have an outstanding reduction of divergence, changing what would be a 100 foot wide spot at 10km away to a 10 foot wide spot.

Here's a comparison graph showing the difference a 10X beam expander can make for a DPSS 532nm laser:

beam_diameter_w.jpg


The above graph doesn't do what is really happening justice when they use a non-linear step from 1 km to 10 km on the end of the graph, it should be ten times longer for the same intensity if using a 10X beam expander, that's effectively increasing the light intensity at a distance to that of a laser ten times more powerful. This means if you put a 10X beam expander on a cheap little 100mw 532nm laser pointer it can make a spot just as bright as a 1 watt 532nm laser diode 10 miles away, not only that, the beam will be just as visible from a 100mw laser pointer with a 10X beam expander on it as a 1 watt laser 10 miles away (of course, not nearly as bright close to the laser source).

Even a slight reduction of divergence can make a very large difference of intensity at a distance as you can see in the graph below:

laser-divergence-graph.gif

Want even better spot performance at a distance without the use of a beam expander? Then buy a pointer with a low power 50mw single mode 520nm laser diode like the PL520. The divergence of single mode laser diodes is so much lower than their multimode counterparts such as the Nichia 1W NDG7475T, the lower power laser can put a terminus spot on the base of a cloud 5000 feet above your head while the 1 watt 20X times more powerful multimode laser diode cannot do so because the light fans out too quickly. Put a 10X beam expander on a low power single mode green laser and now you're cooking with gas compared to a 1 watt multimode laser pointer without an expander, just that the beam isn't very bright, yet it will put a spot on something a tremendous distance away that a 20 watt multimode laser diode could'nt do without the expander, if one that powerful existed.

For myself, in regards to cost and simplicity to get the most bang for your buck a single mode 520nm laser diode coupled with a 10X beam expander is the cats meow for putting a relatively bright spot on something a long distance away, or for the beam to be visible for a longer distance :) - Now that I've said that, the lions meow is a high power multimode or DPSS laser diode with a huge beam expander on it. I have a 160X monster beam expander which when coupled with my 800mw Jetlaser pointer makes a beam so awesome UFO's come to look at it. Unfortunately, I am afraid to use it often for fear of accidentally hitting the windshield of an aircraft I can't see due to its being so far away. The beam output of this 6 inch diameter aperture expander only divergences by a factor of two to become six inches wider for 10 miles of travel and has a beam only five and a half feet wide 100 miles away, 50 feet wide 1000 miles away, a hazard to aliens too.

It's amazing how little expansion there is when using big expanders, the beam only spreads to 5,000 feet wide, less than a mile wide 100,000 miles away, compare that to a run of the mill 1.5 mRad pointer without a beam expander having a 150 mile wide beam that far away, or 5000 feet wide at 650 miles. If I had it spotted on you that far away (a, well, that's not going to happen), it would be the brightest light coming from the surface of the planet at night, not sure how well it would compete with reflected sunlight during the day from that side of the planet.

I used RHD's relative brightness calculator to come up with the relative perceived brightness graphs at this link: http://lsrtools.1apps.com/relativebrightness/?nm1=520&mw1=1000&nm2=455&mw2=1600&useRaleigh=on
 
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More than a fair amount dimmer, it is almost invisible, right on the edge of the visible spectrum, but they make a small dot and burn really well. I like blue, it's very visible and gives you the most for the money. Brightest of all yes is green, even my 82mW 520nm has a visible beam.

Alan
 
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I edited in a whole lot more to my previous post showing comparisons between the cost of 445nm blue to 520nm green in regards to perceived brightness, the green is more expensive any way you cut it, but if you happen to get a high efficiency 1000mw 520nm diode which can be safely driven to 1500 mw of output, then that changes to where they cost close to the same for a given perceived brightness to the human eye.
 




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