DIODE LASER ---Under the hood 13

455nm laser technology is very limited in the materials it can naturally damage. There are all sorts of "tricks" that people have discovered to act as energy transfer agents, carbon black (soot) is one such material that I have briefly experimented with to encourage an engraving effect on glass. My goal in this series is to understand what natural attributes this technology offers and how to best exploit them.
One such major asset is the almost instant power switching available from a diode driven by PWM. For normal engraving or cutting the %power sits at a fixed value and the speed is constant. All the controller has to do is switch the laser on and off. However, there is a mode of operation that turns this laser from a saint into a hooligan. Select GRAYSCALE and you enter a new world. The amazing power switching speed allows the controller to send a DIFFERNT %power for EVERY pixel in an image. This seems to offer a method of reproducing photo images onto a material that has a tonal scorching palette, such as wood or card. My analysis and demonstrations of the focused laser beam properties show that it is unsuitable for such an application because changing the %power changes exposure time and depth of cut , not colour. Yes, there are "tricks" that can create the impression of analog tonal change to cellulose based products but these usually involve chemical infusion. HOWEVER...changing depth of cut for every pixel offers great NATURAL capability for 3D engraving , provided we choose a suitable material and select a speccial DEPTH bitmap image to work with.

[@BleughBleugh]

Fantastic video! Every laser enthusiast should watch this :-)

[@wadhamga]

Have enjoyed the science behind these vids thankyou!
One additional aspect I think would challenge some of the beliefs is to use a fibre grained material such as wood and to do the line test across the grain rather than with the grain and again on diagonals. The light angle that we look at things makes such a difference compounded by the grain angle. Another thing I do is adjust the angle of the item to be lasered so when the piece is put on the honey comb it is adjusted to be etched to match the setting of the scan angle. Said another way the item is eg 45 degrees of the xy axis and the scan angle is 45 degrees. The laser is not overworked by both the x and y doing the angle of the beam changes and instead a 'std' laser x and y action back and forth with x doing the pass and the y shifting after each x pass. The burn does show on some timber grain, fibre and growth ring types to be improved with this method, line spacing is also a huge factor.
One feature in Lightburn that makes dramatic differences is bi-direction versus cross hatch and then when both passes are used in combination, one as a primary depth and the cross as a cleanup in essence. The differences are a big advantage especially when images are concerned or growth rings cause color differences. Improved engrave quality if raised lettering for instance.
So the comment that diode lasers don't engrave is no longer your belief? ;)

[@SarbarMultimedia]

There are many types of laser engraving and you have descibed some of them such as relief engraving to make letters stand out. The ones you describe are all achieved with the depth cutting ability of the laser. For example the layer 1 carbon removed by a cross hatch layer 2, that you describe will have removed material with the laser beam's sharp cutting "point" .Upon enetring the diode laser world I had anticipated that at least the low power 5 watt laser may have a "flat" intensity profile that would allow for SURFACE engraving as I demonstrated with a blow lamp in the first sessiion. You can change the scorching characteristics with a fixed power blowlamp flame by adjusting the exposure time (speed). That encapsultes my definition of SURFACE engraving. If you can scorch without CUTTING into the surface then grayscale engraving becomes possible. The way a CO2 beam works it is possible to turn th power right down and achie an almost flat intensity profile and fuzzy greyscale is possible . The fuzzyness is due to the lack of power change per pixel. The controller sends the correct signals but the CO2 system cannot respond quick enough. The pwm system and the diode are both capable of respoding at high speed but the beam can never be gentle enough to damage JUST the surface , it is always a cutting beam (albeit very poor). SAny graysacle effect you may acchieve will be by trickery rather than natural system capability.
I hope you can now understand my statement about surface engraving.. It is not a belief but a logical and provable fact
However there is a possible depth cutting engraving technique which I will try some time, that has the ability to create a grayscale effect without dithering . One of the characteristics of a "conical" intensity beam is to create different width lines at different powers.. Closely examine this famous enraved image and note how varying the line width is used to create the image. www.gallery.ca/magazine/your-collection/a-familiar-face-unveiling-claude-mellan

[@wadhamga]

@@SarbarMultimedia It will be interesting when you use a higher wattage beam.
It will put theory into practice and probably show the differences better between CO2 and diodes.
The latest diodes with higher wattage are a new ball game I see!

[@wadhamga]

With the Celtic knot if you had started at 20mm/sec would you have removed more and the result being any more passes would be different focal lengths therefore the second then third cut would produce different finish results? ;)
Every pass changes the focal length and the quality and color? ;)
It is also a cause of how eg wood with one coat of paint is almost see through then with a second coat the paint color is dominant, so ... when laser passes remove material the underlays dominate the visual and if painted with something prior that has properties the laser passes can benefit or can lose the image visually same for grain angle versus laser passes and line gap.
A good example was the portrait you did on wood which if the wood was treated with baking soda then a layer of under coat and baking soda then light sand would create a standout image rather than a ho hum straight timber.
Another is timber prep before lasering and sanding with eg 400 grit paper first for images that are not set to be 2.5 or 3D burns versus various preps means that crap wood types can actually produce standout images ... ;)

[@krisknowlton5935]

Actually Russ, we thank you for your time.
We have discussed the use of borax to get a darker 'burn' a while back. Do you think that the borax absorbs the laser light more, thus increasing the heat and burning the wood. What are your thoughts?

[@SarbarMultimedia]

Hi Kris
On a CO2 laser the effect od Borax seems obvious but with just 5 watts and a diode laser itdid not seem to work. Pre-scorching the wood seemed to be the best method of creating a high speed burn with wood. It makes me question just how Borax may be working. With a CO2 laser I have so much power I am now wondering if the Borax is the acting like silver iodide does in photography and is the thing that is actually turning different shades of brown depending on the exposure time you give to it. The fact that I cannot make it work with 5 watts may be lack of power or lack of energy absorption due to the different wavelength. I will test it again when I stop up to 10 watts and 20 watts. We know it works but I am not a chemist so I will have to devise some other experiments to see if the Borax itself has a tonal range of browns as it heats up. If so then we know it's not promting burning in the wood but acting like a photographic film.

[@wadhamga]

@@SarbarMultimedia I wonder if using scratch paper and it being double layer, therefore, the depth makes a difference to assist the impression of darkness which becomes see through layering effect or reflective effect the thinner the top layer left after engraving? Deeper becomes lighter?

[@krisknowlton5935]

@SarbarMultimedia hi, Russ, I never tried it with my 5 watt laser, but I know it works with a 10 watt quite well. I was going to try to video what was happening while I was using this method, but all you can see is a bright light. I guess I should have put my welding helmet in front of the lens.

[@SarbarMultimedia]

@@krisknowlton5935
Hi Kris
My thoughts about staying with the simple one diode 5 watt laser for as long as possible to learn about the effects of 455nm light on different materials turns out to be the right decision. I anticipated that the 10 watt laser would be a simple build up of two laser beams joined up in line like railway carriages. Not so. as you will see in the next video. How this affects performance is a whole new ball game that I shall enjoy investigating. I am sure there will be greater intensity and materials will damage quicker