# What Do All The Laser Specs Mean?!



## ThirstyTurtle (Jun 18, 2013)

So I'm a pretty avid flashlight guy looking to buy my first laser. I'm looking to spend <$50 and essentially want the most bang for my buck in either a green or blue laser but for the life of me I cannot find any good explanation of the specs on a laser. For instance when looking at a new light I'll look at the lumens and know that it's total output, and I'll look at the lux and know that's how far it throws, and maybe I can find some specs about tint, maybe some beamshots so I can get an idea of how much spill it has. But for lasers it's all "mW" and "nm" and sometimes "mm" and there's talk about divergence and such and I can't figure out what it all means so here are some direct questions:

mW - This seems to be total power which is _possibly_ similar to lumens?
nm - So this is wavelength...is this directly linked or related to the color of the laser?
mm - I've read a lot about the cheap 5mm lasers...does that mean the dot is 5mm when you point it at something?
divergence - I assume this is just like the spot and spill on a light. Low divergence means it's a really tight beam and high divergence means it spreads out quicker so it has a larger dot but with less brightness...is that right?

I'd really appreciate some help or even just a link to some explanations that I've been unable to find thus far. 

Thanks guys!

BTW_I might be looking to trade a Nitecore EA4 NW for a laser if anyone is interested...


----------



## bshanahan14rulz (Jun 18, 2013)

ThirstyTurtle said:


> mW - This seems to be total power which is _possibly_ similar to lumens?


 Yep. 5mW and under is what is considered pointer. 5mW=0.005W. More than that, and you should have either assembled yourself, or purchased with the various requirements for a higher power handheld laser device. I don't know the legal jargon, but just know that most lasers are actually technically illegal, so just because it is listed as <5mW doesn't mean it's not pouring out more than that.


ThirstyTurtle said:


> nm - So this is wavelength...is this directly linked or related to the color of the laser?


 This is the color of the light. a light wave's physical property of color is defined by its wavelength.


ThirstyTurtle said:


> mm - I've read a lot about the cheap 5mm lasers...does that mean the dot is 5mm when you point it at something?


 < probably. This is one of those values that most sellers just guesstimate @ 5mm.


ThirstyTurtle said:


> divergence - I assume this is just like the spot and spill on a light. Low divergence means it's a really tight beam and high divergence means it spreads out quicker so it has a larger dot but with less brightness...is that right?


 Yep. Again, one of those guessed-at measurements. This depends on how accurately it was focused by the worker in the factory.


----------



## ThirstyTurtle (Jun 18, 2013)

Thanks for the help!

I'm wondering if there are some standard wavelength values for the various colors? (Red, green, blue, purple). Also, are any of the colors better than the others or is it purely a matter of color preference?

What kind of mW values should I be looking at? I mostly want to be able to see the beam very very clearly at night and for it really have some "wow" factor over your typical red $5 laser pointer. I plan on reading all safety information and acquiring necessary equipment (safety glasses etc.)


----------



## bshanahan14rulz (Jun 19, 2013)

I personally can't recommend anything over 5mW, but I'm not going to say that higher powers aren't available. Just let it be known that lots of surfaces are reflective, and some bad luck or judgement can leave a permanent injury.

That said, let's move on to brightness. 
http://en.wikipedia.org/wiki/Luminosity_function
What this basically says is that if you had a red, green, and violet laser pointers, all with power output of 5mW, the green would appear the brightest because the cells in our eyes can "see" wavelengths around 555nm the easiest. 

As for the most easily obtainable wavelengths?
Red: 660nm. A very deep red, very typical laser pointer red.
Red: 635nm. A slightly more orangey red. By itself, it just looks bright red. Eye slightly more sensitive to this wavelength, so will appear brighter than 660nm.
green: 532nm. All green lasers are this wavelength due to the miniaturized classical solid state laser cavity's frequency doubling process. Brightest color per power.
blue: 445nm, 450nm. Come in very high power varieties (>1W) and lower power single mode varieties (~50mW). High power lasers have a wider cavity for more transverse modes. Think a single laser cavity, but creating lots of lasers inside that cavity to use up more of the area in it. The result is that the beam is hard to get low divergence figures. Single mode variants are easier to get a cleaner dot rather than a line. 
violet: 405nm. Pretty good for fluorescence testing. Not easy to see. Not very bright. almost always are single-mode.


----------



## ThirstyTurtle (Jun 19, 2013)

bshanahan14rulz said:


> I personally can't recommend anything over 5mW, but I'm not going to say that higher powers aren't available. Just let it be known that lots of surfaces are reflective, and some bad luck or judgement can leave a permanent injury.
> 
> That said, let's move on to brightness.
> http://en.wikipedia.org/wiki/Luminosity_function
> ...



Thank you SO much for all the useful information!

Honestly I'm not dead set on a higher powered laser, not looking to pop balloons or light matches, I primarily just want to be able to clearly see the laser "beam" not just the dot in the dark. I would almost prefer a 5mW so I don't have to worry AS MUCH about injuring my eyes or someone else's. 

So will I be able to see the beam of a 5mW green well in the dark?

If I got a 5mW I'd want to buy a decent one but I feel like I might as well buy a cheap high-powered one as opposed to a good low-powered one if I'm only going to use it very rarely. 

What do you guys think?


----------



## ThirstyTurtle (Jun 19, 2013)

Okay so I'm considering getting this _dirt _cheap laser:
http://www.ebay.com/itm/5mW-5-mW-53...2514?pt=US_Laser_Pointers&hash=item2eb2d7a4e2

It's spec'd at 5mW but on some other laser pointer forums a lot of testing has found them to be 40-100mW which sounds like plenty. I'm wondering what goggles would be adequate to use with this? I don't want to buy goggles that aren't the right spectrum or rated for that power or something. Any guidance?

Thanks!


----------



## bshanahan14rulz (Jun 19, 2013)

I would actually ask that on the forums you found. Cheaper goggles are generally frowned upon, but some do get decent results. I use a red lensed goggles, no brand name. Got them from a member over there, actually. From a 120mW source, what isn't filtered is barely visible, so I'm guessing at <1mW got through. I only purchased these cheap goggles after someone else with a power meter tested one from the batch. N=1 isn't the best sample size, but I made sure to verify for myself that it was adequate for my devices and eyeballs.

Infrared and near infrared is a different story. As I mentioned earlier, green lasers are almost always a solid state laser that has been frequency doubled. This process (abbreviated as DPSSFD, or DPSS for short) is much more interesting than put electricity into diode, have laser come out the other end. For this process, a piece of special glass doped with neodymium emits laser radiation when pumped with energy that it can absorb. It gets this energy from an 808nm laser diode, and emits laser radiation in a little bit deeper IR, @ 1064nm. This 1064nm laser is then sent through a special optic that doubles the frequency of certain wavelengths. Because of maths, when frequency doubles, the wavelength is halved, coming to 532nm. This is the green beam you see coming out the front of the laser. Now, this process isn't perfect, so along with that 532nm radiation, you are also going to get some 1064nm and even 808nm leakage. While goggles for green lasers will block a specified amount of 532nm, they make no claim as to protection against IR. An IR filter will block out those two and leave only the 532nm photons to pass through. However, laser pointers almost never come with an IR filter built-in. You can ask over at the laser pointer forums about where to buy little IR filters, they might be able to point you in the right direction. 

FYI, I have a 30-40mW, 532nm overspec pen, and it is pretty darned visible at night. 
Also, check your local laws and where your location is with respect to airports. Law generally states no lasers within a certain radius of an airport, and no lasers in or around a plane's flight path. The specifics can vary depending on location.

Be safe with those photons!


----------



## Eidetic (Jun 24, 2013)

If the goal is to see the laser beam, goggles defeat the purpose. There is a laser pointer forum where you can read all about safe handling of laser light. Google "laser safety". Green lasers are the most visible. Visibility of the beam (not the "dot") depends on how many particles are in the air. More dust, more visibility for any given laser output power.


----------



## MichaelKelley (Jul 14, 2013)

Thanks for sharing this wisdom!


----------



## Sigurthr (Jul 14, 2013)

I'll just add to this and state that beam diameter for a given power (mW), wavelength (nm) and atmospheric particle density is inversely proportional to perceived beam brightness. Also, the closer the wavelength is to 555nm the bright it will be if all other parameters are equal. 561nm DPSS is actually the brightest per mW but is very rare and expensive. Of all the commonly available wavelengths it is 532nm that would be the brightest.


----------

