Laser Engraving

Regarding safety:
While I am prepared to put up with cheap goods until I experience reasons fro getting better items, laser light and eyes come into a different league. You can get appropriate wavelength blocking goggles for use with lasers on ebay from Asian sources reasonably cheaply. However, I'm not really prepared to trust these without positive recommendations from laser cnc users - what do experienced users recommend?
Once I am protected from the laser light - what are the safety concerns for people who inadvertently enter my workshop when I am laser engraving? Is there a normal square-law reduction in laser light power? Is it just direct beam light that damages the eyes or any incoherent light reflected off surfaces and entering the eye? Currently I have my cnc machine fully enclosed in a see-through box with an access window at the front. Would people recommend I black out the sides with plywood (say) and enclose a small video camera inside to monitor operations - or is this taking it all a bit too far?

Micromet wrote: Is there a normal square-law reduction in laser light power?

It will depend on the focus. For a perfectly collimated beam there is no reduction in intensity with distance (in a vacuum, and perfectly collimated).

The inverse square law is a consequence of the "thing" being distributed over the surface of a sphere of increasing radius. The intensity decreases proportional to the increase in area of that part-spherical surface.

So, with focussing optics you probably do get an inverse square, but any reflection is likely to interfere with that in unpredictable ways.

I would ask the laser supplier if they have any goggles that they sell or recommend for the laser they sold you. And lock the door when using the machine to keep the cat out.

given what Andy's beat me to , lol .
watch out for reflective light , more than anything , and as the diode is effectively pointing down and fixed you shouldn't have any problems . you'll find even a clear sheet of perspex between you and it will be fine ,
and of course NEVER EVER look directly into the diode , up at cutting wavelengths that becomes a different matter , as at 10.7 their invisible . and if your not careful will give you a good suntan after 20 mins or so .
but your using totally different lasers, which are only really good for burning ( some people think it's cutting but it's not , it's really just burning it's way through ) , one other tip dont have glossy surfaces around the laser it can bounce off .

whilst the laser is off the machine then always be careful of where it's pointing etc ,
your more at danger when it's being fitted or your adjusting etc , than any onlooker , always have the power off when your handling it
laser glasses are fine for these low power diodes , it's more serious when your working with 2 - 5Kw lasers , where i use ce marked glasses and i know their pedigree and get them checked every 2 years .
being behind say a 1/4" of clear acrilic will be fine for onlookers ,or tinted for example .

en.wikipedia.org/wiki/Laser_safety

I think, to make things easy in the first instance, I will just monitor the temperature with the thermocouple using my DVM input and investigate better heat dissipation with larger heatsinks or fans. I'm not sure I want to go down the water-cooled path if I can avoid it. I'm a great believer in Occam's razor. Having done all that I can then assess whether I need to control the output of the laser for high temperatures.

it's all down to how long the laser is on for , the cooler it is the better it works , and the less stress it's under , which ultimately give you how long it will last !
they are highly susceptible to temp , humidity , voltage and current , and just about everything else on the planet , use the largest copper heatsink you can find , as you appear to want to do raster engraving.

Thanks cncbasher.
As computer CPU's also need to be cooled effectively, and I have several old fan-based CPU copper cooling units lying around, I will try and adapt one of these to cool the laser. I can then monitor the temperature as I slowly raise the power output of the laser.