100mw green from lanling tec

Hi people I have just received a 100mw green laser from David lanling , http://cgi.ebay.co.uk/100mW-Green-La...QQcmdZViewItem I purchased it from ebay only took 4 days to arrive as did my red laser I purchased a couple of weeks before, very pleased with it to start off with the beam in my front room looked well collimated at around 2 mm and it did appear to look around the 100mw maybe a bit more , it was not until it got dark and I took it outside and fired it up to the top of my garden that I realised I had a bit of a problem the beam at around 60 feet was about 2 inches, I nearly fell over, I had no doubt for the asking price it was not going to be TEMoo but I did not think I was going to buy a green flash light either, blowing the warranty straight away I undone the front face plate off and tried to get the beam size down to as small as it would go, after trying for an hour the smallest spot size I could get was about 1.5 inches at 60 feet all my other lower power lasers are around the ¼ inch to 3/8 of an inch mark am I being paranoid or do you think I have a duff unit what sort of beam size should I expect your thoughts on this would be greatly appreciated , great site by the way at last I have found some people with the same interest as my wife has had enough of me babbling on about lasers lol :confused:

Sounds like you've got a problem there. Have a look at this composite image I put together a while back. All the measurements were taken at 105 ft from the laser head. Even my worst laser has a smaller beam spot at 105 ft than your laser does at 60 ft. Something is wrong...

http://photonlexicon.com/albums/dlre...mage.sized.jpg

I'd get in touch with the guy that sold you your laser ASAP and ask him what the deal is.

Adam

Damn, that is big... Now you got me wanting to shoot mine out a window so I have the distance to measure mine... :p ;)

most of my lasers measure about 3.5 to 4 inches at 170 ft ( from booth to scrren)

nice chart adam,looks like i need a longer garden lol, i spent abot 3 hours on it today.I took it apart messing up any warrenty that it had but had good fun doing it,during the day it was less strain on the eyes, it appears to have a respectable 1/4 inch dot in the middle of a 1 inch slightly less bright beam when viewed looking at the beam termination against the house, i ahve not got a meter to measure what this thing is puting out but it looks to me to be around the 120-140 mark, i took the main front focus lense off and shone it against a piece of black card ,there it was again this much uncollimated cone of light with a brighter spot in the middle, to cut along story short after tweaking the power input brining it down to something around the 80mw the beam did tighten up a bit, peronally i think that its the 808nm diode focusing that is a bit out making the beam not pass through the nd:yv04 crystal that good that is my guess if thats the case im in trouble lol i did get round this when i took the main focus lense of the front i stuck a less powerfull lense to refocus the beam got it down to about 5 mm which was great but the beam was 5-6 mm at the laser end so there was no hope of being able to use a scanner with it like that by the way obviously depending on scanner mirror size what is the rough max beam size you can scan as i am in the next couple of days going to order one from laser show parts

Kaz I doubt it will be the focus of the 808. This output of the pump diode isnt always focussed anyway but is expected to couple into the Vandate at a pretty small size - often the laser diode (pump diode) is positioned as close to the Vandate as possible so that even with the huge divergence the spot is still small creating the greatest power density in the crystal. What you have to consider is that a DPSS contains 2 laser systems. One is the pump diode and its beam path and optics (if any) being fed into the Vandate. The second is the vandate/KTP/OC system. Im your case I suspect this is the cavity that is not right. It may be that the OC needs tweaking to suppress extra modes that are casusing the halo around the main spot, if you cant get the beam spot down at distance by focussing the output lens alone.
Yes the pump input will have an effect on the output and I think the improvement you are seeing when you lower the power is as a result of less modes being active at a lower power level. You can clean up the output modes by matching all the alignment and internal components better but this may mean ripping it and rebuilding it - maybe making some new parts. You have to look at how feasable this is but you may end up with a laser that has less power overall.
Maybe this is the explanation as to why these lasers from DL are seemingly so cheap. You do get what you pay for.

Rob

PS some pix of the insides would be nice :)

thx for that Rob, thats the problem of having a cheap multi mode i surpose,it did'nt even cross my mind to take photos should have done as they say a picture paints a thousand words, and i know you guys love photos, if it was'nt for the fact it was a pain to put back together i would take it apart again just to take some photos lol any projects in the near future i will take some pics, that should not be to long as i have the cheap galvo set coming from laser show parts, i know a little bit about lasers but i know nothing about galvo's reading the posts on hear helps thx Paul

The galvos that they sell at Lasershowparts.com have larger mirrors than either the DT-40's or the Cambridge scanners I've seen, so you should be OK. As a rule of thumb, you'd like your scanner mirrors to be at least double the width of your beam (more is better). But when you get into high power red diodes (especially 635 nm), you often have to accept the fact that some of the beam is going to spill off the edges of the scanner mirrors.

Still, with a 100 mw dpss green you should have a 2-3 mm beam diameter at the aperature. That ought to fit on any scanner mirror. A 6 mm beam is quite large for a 100 mw green - I don't know if it will all fit on the scanner mirrors or not. (A large beam will still work, but you might loose some power around the edges.)

Adam

Thanks Adam, the info has helped alot, the beam from the laser aperture is about 2mm but its the far field divergence thats the problem, so it will be fine to scan by the sound of things cant wait to get me hands on them i have read all good things about Lasershowparts.com in the posts