Some test shots with my new arduino and agilent powered fiber laser

[KTP]

Heh ok, the laser is made by IPG and was an ebay score.  I used an arduino to simulate the controller since I didn't have one and I am using the function generator output from my MSOX3024A to generate the repetition rate pulse stream (not required if you just use the default 20khz built into the unit).

I made a photodiode circuit using a too large area and capacitance photodiode from my junk box, but I figure it has a rise time of less than 10 to 15 nanoseconds reverse biased with 10V.  I feed it into the 50 ohm input of the Agilent and captured the light pulses from the fiber laser.  The laser outputs about 10 watts average power in a 100ns 0.5mJ pulse (so 5000 watts peak power in that pulse).  It can do 20,000 to 100,000 of these pulses per second, so for all practical applications is close to CW.  You get the highest peak power pulses at 20khz.

What makes this laser interesting is the incredible high quality of the beam.  It can be focused down to under 0.0005 inches or so (10um).  This is pretty much impossible with diode lasers, except maybe some of the deep blue single mode versions.  They are not q-switched anyway, so they don't have that metal melting peak pulse power.

I found a lens from a old medical laser...I think it may be AR coated for 1064nm but not 100% sure.  If it isn't coated I am losing power.  At any rate it was good enough for some test shots.  I first shot the unfocused ~6mm beam at some laser test paper to check the spot.  I then switched to the lens, a 1/2 inch diameter plano convex with about a 20mm FL.  It punched right through aluminum foil so of course I upped the game and grabbed a razor blade.  A couple of the first shots were out of focus but some rough movement got two shots in focus enough to blast through the razor blade.  I am quite pleased with how small the holes are.  In the zoomed in photo I did my best to take a shot under the microscope with the razor illuminated from the front and the rear...the black line is a human hair about 20um in diameter.  The holes are 1/2 to 3/4 the diameter of the hair, although they look bigger in the photo because my camera skills are lacking.

I am wearing full goggles rated OD10 at 1064nm and I am in a closed room.  I also use a webcam to view the laser instead of looking directly at it.  Reflections can even be dangerous at these peak power levels.

Next step is to build a um resolution cnc xyz stage.  Luckily I have the brushless servo ballscrew linear actuators, so this should go together quickly.

[MacAttak]

Looking forward to this once you get it working on a shark mounting system.

[KTP]

Looking forward to this once you get it working on a shark mounting system.

Going to start in baby steps...angry sea bass.

[NiHaoMike]

Looks like a great setup for DIY PCBs. It might be able to directly laser etch the copper, but if not, it would certainly be able to etch a black paint mask.

At Texas A&M, they use a CO2 laser to "print" PCBs. They would coat the boards with lacquer, etch that with the laser, chemically etch the copper, drill holes, and plate the vias.

[KTP]

I am pretty sure it can remove 1oz copper from a pcb but I don't know what the removal rate would be.  It definitely could drill the holes in the pcb too.

I will probably try some experiments with that even though I usually just get my pcbs made by a shop.

[MacAttak]

Isn't copper nearly 100% reflective at that wavelength? Seems like pointing a high-energy infrared laser (1064nm is infrared I think?) into essentially a mirror would be a Really Bad Idea (even one covered by a mask which would quickly break down).

[KTP]

Isn't copper nearly 100% reflective at that wavelength? Seems like pointing a high-energy infrared laser (1064nm is infrared I think?) into essentially a mirror would be a Really Bad Idea (even one covered by a mask which would quickly break down).

It is the nearly part that makes the difference.  Copper is indeed one of the harder metals to cut with IR but if I can focus the spot down to 10um the peak intensity will be in the multiple megawatt range.

I will run some numbers though and see if it is realistic.  I need to look up how thick 1 oz copper is..can't recall.

[mikeselectricstuff]

LPKF sell a machine for laser-cutting PCB, but I can't see any indication of wavelength or power
http://www.lpkf.com/products/rapid-pcb-prototyping/laser-circuit-structuring/laser-structuring-printed-circuit-boards.htm

Your laser should certainly be good for stainless stencils though.

[poorchava]

or maybe a simpler approach: cover the laminate with spray paint, then use laser to make openings and then etch in etching solution of your choice. plastic reflow stencils should also be a breeze.

[MacAttak]

I need to look up how thick 1 oz copper is..can't recall.

Google tells me 1.4 mils.

[KTP]

I need to look up how thick 1 oz copper is..can't recall.

Google tells me 1.4 mils.

Ok, so about 35um.  I found some info on the web that shows direct milling of copper traces using a 40 watt fiber laser.  Mine is only 10 watts average power but 5000 watt peak power pulses.  If they can do it with 40 watts, I might be able to do it with 10 watts at a slower feedrate with a smaller spot.  I would most likely want at least a 35um depth of focus to maintain the vaporization energy through the copper.

I am going to get a achromat doublet from Thorlabs to experiment with.  It should give a significantly tighter spot than a single element plano-convex.  I am not very comfortable picking optics, but I was thinking of going with the 1 inch diameter 40mm focal length cemented doublet.  It has a destructive rating of 5J/cm^2 for a 10ns pulse...my little laser is well below that so I don't need the air spaced doublet with a 10J rating that is $525!

with a 6mm input beam and a 40mm focus, I should have a spot size of about 11um using a M^2 number for the fiber laser of 1.2.

The Rayleigh range I calculate with this, again using a M^2 of 1.2 would be 75um.   Considering the copper is only 35um thick, this would indicate I would have consistent high power throughout the cut.

Now how much intensity do I have in a 11um spot?  If the peak power in my 6mm diameter beam is 5000 watts then the intensity is 17,700 watts/cm^2. If I reduce the beam to 11um diameter, then I have increased the intensity by 545^2 or around 300,000 times.  This gives me an intensity in the focused 11um spot of around 5.3 gigawatts/cm^2.  Pretty bright.

[LukeW]

I found a lens from a old medical laser...I think it may be AR coated for 1064nm but not 100% sure.  If it isn't coated I am losing power.

Cool.

It's a Ytterbium doped-fibre laser, so it will lase at something like 1080nm IIRC.

So anything that's designed for use with neodymium at 1064nm, for example your lens, and your safety glasses, will be slightly off their intended wavelength, but it's very close, so should be close enough.

[bobhaha]

This is a fine example of a ND:YAG laser in action!

Just for reference it lases at 1047-1079 nm depending on impurities and doping quality.

I have a ND:VO4/KTP crystal set for doubling the frequency to 532nm. Not sure about the power density rating on it though... probably in the 1-2W range. If you want to give it a go shoot me a PM.

I'd love to see more pictures of this unit... It's extremely hard to get your hands on a compact unit like the one you scored, over here in Australia.

-Adrian

[KTP]

Some success. I bought a set of (non-stainless) feeler gauges to get some different thickness than the 0.009" standard razor blades.

I also turned a copper nozzle, or at least an artist's conception of what a nozzle might look like since I really have not a clue.  I drilled a 0.045" hole for the beam exit and tapered the inside and outside.  I found a old section of tube in my junk box to press fit the nozzle into, and also a section with a hose input.

Mounting up the 0.005" thick feeler gauge, I set the 75% argon/25% CO2 gas feed to 30 PSI. I then cut some rectangles that are 0.02" wide by 0.03" high. I tried feedrates of 0.6 IPM, 1 IPM and 2 IPM. The 2 IPM actually seemed to leave the best cut. I have not tried faster yet.

There is still some brownish/red smudge around the cuts and some dross on the top and bottom side, but definitely less than when I was running with no nozzle or gas. These tests are all with a cheapy plano convex single lens of about 30mm FL. I will be getting the hopefully much better achromat doublet from Thorlabs this Monday.

The pictures show the rectangles cut out next to a 0805 resistor for a sense of scale. There were three pieces but I sneezed and one went flying somewhere. The last pic is the very comical setup I have for this on my Shizuoka cnc bedmill. Imagine a 7000 pound cnc mill being used to cut out a square that is 0.02" by 0.03" by 0.005"! I do plan on building a xyz stage out of some NSK linear robot modules very soon. Always being safe, I am in a closed room wearing OD10+ goggles and not staring at the beam. Until this gets into a closed box system I am being extra cautious.

I would like to try some variables to see if I can get an even better cut. I did all of these at 20khz rep rate....perhaps going to 40khz or even higher might improve things. Suggestions?

[KTP]

I hooked up a gas solenoid and a laser on/off line from my cnc controller so I could run some standard g-code programs for testing.  I created a 16 tooth spur gear and generated the g-code for it.  At first I made the gear less than 0.03" in diameter but that was too small for this lens and also I forgot my cnc has 0.0015" backlash in the x-axis ballscrew (not worth replacing for most of my work).  When trying to cut teeth in a 0.03" diameter gear, 0.0015" of backlash just kills you.

In the larger gears (about 0.07" in diameter) you can see the effects of the backlash in some of the poorly formed teeth.  There are a few good teeth and all of the gears of a size have the same defects in the same area which confirms that the culprit is backlash and not the laser or lens.  It will be nice to get the achromat doublet for a signicantly tighter beam but I need to switch from my cnc metal bedmill to the Adept ballscrew linear robot modules I happen to have.  These have zero backlash and 1um position.  The cnc mill was just faster to do a proof of concept of the fiber laser being able to cut thin, small stuff.

I wonder if I want to keep moving the workpiece when I build with the Adept modules or if I want to do sort of a flying optic arrangement.  Or maybe move the workpiece in x and the optics in Y, Z...

So many fun things to try, and I haven't even started trying to play with micro welding or soldering or sintering or scribing...

Maybe it is time to start thinking about nanobots      Checking ebay for x-ray lasers!