Why can blue lasers burn thing better then similar powered IR lasers? - Page 1
Forum section: electronics / general

author: Beamin
author_rank: Super Contributor
timestamp: July 28, 2018, 10:19:11 pm
content: When I started playing with laser diodes ( DISCLAIMER: Yes I had proper eye goggles for the color and a table with fixed optics and walls around it so that accidents didn't happen. In case this forum is like other laser forums where people just lecture on safety rather then assuming you know what you are doing, even though I have no idea what I'm doing, and actually answer questions) ANYWAYSI thought the IR would be better at heating objects from a distance then the blue or green ones. I wanted to heat some chemical reaction remotely or speed up certain spots while allowing others to remain cool. I had thought if you want heat you want IR. Thats not the case the shorter wave length has more energy. But since I don't have a good understanding of the math I wanted to figure out why blue has so much more heating power then green at 540nm. Does the energy scale linearly ie 500 nm at 1 watt is half as powerful as 250nm at 1 watt? If so wouldn't the purple or UV/blacklight handheld laser pointers be just out right dangerous? I want to get a purple/black light laser diode to cure UV resins in very specific spots to adhere things with more precision then you could get trying to glue things together. I saw on the juian Ilette channel him curing with what he called an UV laser with little or no safety protection. I have a blue laser diode and there is no way I would be just shinning the thing around like that. I would have goggles, and the work piece and diode clamped to the table with a back stop. Perhaps its a really low wattage? Does the youtube "styropyro" guy frequent this forum like many others?When a green or blue photon hits an atom it reradiates off an IR photon. What mechanism causes this. Is it phonons or molecular bonds? Or does it actually cause atomic orbitals to jump up and then back down? Wouldn't that mean it's ionizing only able to be done by UV? What the exact lowest UV wavelength and which are the lowest energy orbitals? Xrays will jump all the way down the 1st (2 electron/He) or second (8/Ne) orbitals whats at the other end?Heres another fun fact a friend of mine was showing us his green laser pointer was safe so he pointed it at his arm while it was focused. He did it to my friend who had really black skin and he jumped and said it felt like needles were going into his skin.

author: CopperCone
author_rank: Super Contributor
timestamp: July 29, 2018, 01:27:39 am
content: did you actually measure the power output of the laser for parasitic infrared energy that leaks through the crystals? chinese will basically post the power at a certain frequency not the total output power of the laser, meaning that you can have several watts of infrared energy that is bleeding through a crystal that makes 500mW for instance. A good laser will either use a different method of generation that is spectrally pure or will use optical filtering to make a reasonable output profile. Compact semiconductor lasers are relatively spectrally dirty compared to gas lasers.If you don't have lab equipment lasers, and you buy a laser power meter, you will be surprised what you see. To further the experiment you would get a monochromator and a broadband attenuator to protect the monochromator.this is also a question of color and surface texture, i.e. infrared will see brushed steel like a mirror through a thermal imager but if you look at it optically it will look like brushed steel. surface emissivity/reflectance/etc

author: raptor1956
author_rank: Frequent Contributor
timestamp: July 29, 2018, 03:20:02 am
content: It depends on the material -- the industrial lasers used for cutting steel etc are best suited for some materials and less suited for others. The fiber lasers that are becoming the most common for such applications actually need a lot more power to cut through Aluminum than steel.Partly this is simply the absorption characteristics and partly the finish.Microwaves heat the water in foods because the frequency (wavelength) is a perfect match of the H2O molecule.Brian

author: raptor1956
author_rank: Frequent Contributor
timestamp: July 29, 2018, 03:46:07 am
content: Quote from: blueskull on July 29, 2018, 03:22:45 amSay what?Brian

author: NiHaoMike
author_rank: Super Contributor
timestamp: July 29, 2018, 04:00:51 am
content: Quote from: CopperCone on July 29, 2018, 01:27:39 amThe blue and violet lasers commonly available are diode lasers and do not emit much infrared, not DPSS.

author: raptor1956
author_rank: Frequent Contributor
timestamp: July 29, 2018, 06:30:33 am
content: Quote from: blueskull on July 29, 2018, 04:07:07 amDoesn't change the fact that microwaves heat the water! Yes, the freq/wavelength is sub-optimal owing to the spectrum requirements, but in the end the microwaves heat the water! However, water is not the only thing heated by 2.45GHz radiation so in some situations the heating is partly water and partly other things.Brian

author: Beamin
author_rank: Super Contributor
timestamp: July 29, 2018, 09:49:11 am
content: Quote from: raptor1956 on July 29, 2018, 06:30:33 amYes I first noticed this when I put olive oil in the microwave and it heated it. That shouldn't happen if 2.45GHz is tuned to the length of the V shaped bonds of H2O. How exactly do microwaves heat oils? Can they heat other things or non liquids? I saw a video where a guy microwaved some pills for 10 minutes to break down the binders in them. I bet his microwave didn't last long as there was no water in it.

author: nfmax
author_rank: Super Contributor
timestamp: July 29, 2018, 10:36:16 am
content: Quote from: Beamin on July 29, 2018, 09:49:11 amBecause both oils and sugars contain hydroxyl groups, which are electrically polarised, and respond in a similar way to the microwave fields as do water molecules. Muchmuchmore detail here:http://www1.lsbu.ac.uk/water/microwave_water.html

author: David Hess
author_rank: Super Contributor
timestamp: July 29, 2018, 06:12:07 pm
content: QuoteThey heat anything in proportion to the dielectric loss at the frequency of operation. This is actually a good test if you want to find which materials are good for low loss inductor and capacitors forms and you could apply the same test to dielectric fluids as well.The variation in dielectric loss for liquid water between 900MHz and 5.0GHz is not significant. Water vapor on the other hand has a minor peak of loss at about 25GHz.We once cooked hot dogs in an HF tank coil.

author: BillB
author_rank: Unknown
timestamp: July 29, 2018, 06:32:39 pm
content: Quote from: David Hess on July 29, 2018, 06:12:07 pmHow did they taste?

author: David Hess
author_rank: Super Contributor
timestamp: July 29, 2018, 06:53:26 pm
content: Quote from: BillB on July 29, 2018, 06:32:39 pmThey tasted hot doggy as expected.

author: NiHaoMike
author_rank: Super Contributor
timestamp: July 29, 2018, 07:40:26 pm
content: Quote from: David Hess on July 29, 2018, 06:12:07 pmThere was once a gadget for sale that cooked hot dogs by connecting them to the mains.

author: Wolfgang
author_rank: Super Contributor
timestamp: August 04, 2018, 02:45:55 pm
content: I would guess that UV and blue is much better absorbed my many materials.Not just humans get a sunburn from UV

author: Zero999
author_rank: Super Contributor
timestamp: August 04, 2018, 04:06:32 pm
content: To answer the original question: no, blue lasers don't burn things better than similar powered IR lasers. The ability to burn something is related to how well it absorbs the radiation emitted by the laser and the power density of the radiation falling on the said object. An object which absorbs 90% of the radiation falling on it, will be subject to exactly the same temperature rise, given the same laser beam width and power level, regardless of the wavelength.

author: innkeeper
author_rank: Unknown
timestamp: August 04, 2018, 04:17:40 pm
content: good explanation here:https://www.quora.com/If-UV-rays-are-more-energetic-why-do-they-generate-less-heat

author: Zero999
author_rank: Super Contributor
timestamp: August 05, 2018, 08:27:22 am
content: Quote from: innkeeper on August 04, 2018, 04:17:40 pmThat's link deals with thermal radiation, which broadband and is totally different to narrowband laser radiation.

author: Beamin
author_rank: Super Contributor
timestamp: August 11, 2018, 04:11:44 pm
content: Quote from: Hero999 on August 04, 2018, 04:06:32 pmBut they do though. Get two colors of laser diodes with the same power output the green won't burn like the blue will. Green will light a match only while the blue was outright dangerous. And for fun the green was a IR pumped laser (1008 to 504nm or something like that) that had just as much IR out as green so really double output of the blue, yet I know which one I would let light up my skin (not saying I'm really white, but green lasers ARE racist: had a friend it would burn while I was fine!).

author: Wolfgang
author_rank: Super Contributor
timestamp: August 11, 2018, 04:18:08 pm
content: Dont stare into beam with remaining eye.