How to calculate handheld laser power from mW to J/cm^2 - Page 1
Forum section: electronics / projects

author: Michael_P
author_rank: Contributor
timestamp: November 12, 2015, 01:34:16 pm
content: Hallo,can some one help Im looking for simple laser that will have 5 J/cm^2the problem is that in all offers in expresses there are other parameters than J/cm^2How to calculate 100 mW to J/cm^2?if they give this paramters

author: T3sl4co1l
author_rank: Super Contributor
timestamp: November 12, 2015, 01:43:59 pm
content: J/cm^2 is an energy density per area, it is meaningless in reference to a continuous power output.Tim

author: Michael_P
author_rank: Contributor
timestamp: November 12, 2015, 02:33:27 pm
content: Quote from: T3sl4co1l on November 12, 2015, 01:43:59 pmOK, I agree but how to calculate? this reference look like challenge

author: CM800
author_rank: Frequent Contributor
timestamp: November 12, 2015, 03:03:00 pm
content: I'm assuming you are trying to work out how much power the laser will be able to apply to a specific area.Watt = Joules per SecondW=J/Sso you would have to work out how much power you get from the laser over a specific area (It will depend on distance, beam quality and the air / fluid it passes through)so you would measure the size of the laser's dot and get that size in m2lets say it is 1mm2(1x10-6m2)From there, work out the duration of the laser power (lets say 1 second)100mW = 100mJ / 1sso every second you will be applying 100mJ to the area of 1mm^2.so...J / S / m2therefore the answer is:10J/s/cm2(joules per second per cm^2

author: LaserSteve
author_rank: Super Contributor
timestamp: November 12, 2015, 03:11:24 pm
content: Be aware that the laser listed will have a elliptical beam. All direct diode lasers without beam shape correction optics are elliptical due to device physics.Steve

author: T3sl4co1l
author_rank: Super Contributor
timestamp: November 12, 2015, 10:57:17 pm
content: Quote from: Michael_P on November 12, 2015, 02:33:27 pmYou don't...Again, it's meaningless.Do you have a purpose in mind? Do you want to deliver energy in a known time frame? Is there some other specification or background information you could tell us? Anything at all..........??Tim

author: TimFox
author_rank: Super Contributor
timestamp: November 12, 2015, 11:08:38 pm
content: To go from watts to joules, you need time. Normally, this would be a pulse duration to get joules/pulse.To get joules/cm^2 from joules/pulse, you need to specify the distance from the source, and know the solid angle into which the source emits (inverse-square law).

author: Michael_P
author_rank: Contributor
timestamp: November 13, 2015, 02:11:47 am
content: Quote from: TimFox on November 12, 2015, 11:08:38 pmI want to get something like is in this publicationhttp://www.ncbi.nlm.nih.gov/pubmed/24871130

author: T3sl4co1l
author_rank: Super Contributor
timestamp: November 13, 2015, 03:22:30 am
content: Hmm okay, so they've delivered a dose of laser energy to a sample, I suppose. Does the paper mention what duration of pulse, power level, etc. was used?Tim

author: Michael_P
author_rank: Contributor
timestamp: November 13, 2015, 05:27:30 am
content: Quote from: T3sl4co1l on November 13, 2015, 03:22:30 amIf I good understand optiamal will be 5 min a day, dose about ~4 J / cm^2Quote

author: SteveLy
author_rank: Regular Contributor
timestamp: November 13, 2015, 06:55:53 am
content: Without knowing more about what you're trying to do it's hard to give advice. Wanting a certain J/cm2 is not meaningless. If you know the power output of your laser in watts and the (effective) spot size of the beam then from the desired J/cm2 you can calculate how many secons/minutes you will need to keep the target illuminated to deliver so many J per cm2.This J/cm2 quantity is not a property of the laser, which is why you can't find it in the data sheets. It is up to what you do with the laser. Note: W = J/s. J is a unit of energy, W is a unit of power.

author: Michael_P
author_rank: Contributor
timestamp: November 13, 2015, 08:54:34 am
content: Quote from: SteveLy on November 13, 2015, 06:55:53 amAt first I want know "How to calculate handheld laser power from mW to J/cm^2"supouseif we chose to use power 100mW laser diode at given assumption 10 mm from target for 300 sek., how many J/cm^2 can be absorbed by target? (diode data sheets as in first post)

author: SteveLy
author_rank: Regular Contributor
timestamp: November 13, 2015, 09:04:37 am
content: 100mW is 0.1W = 0.1J/s. Sustained for 30s it will deliver 0.1J/s x 30s = 3J of energy. Over how many cm2 that is will depend on the spot size (beam diameter) of the laser. But just divide 3J by the illuminated area in cm2. Distance to target does not matter at such short distances because the divergence of a laser beam will be negligible.

author: LaserSteve
author_rank: Super Contributor
timestamp: November 13, 2015, 03:52:17 pm
content: I currently work at a university, I pulled down the academic paper listed above, accessed on 11/13/2015. I hereby include a paragraph of it under the US Copyright Scheme Educational Use Clause, and for Laser Safety Purposes.I Quote the hardware portion of the paper:Laser treatmentsIn vitro assaysA near-infrared laser was used in all experiments. Specifically, an 810-nm GaAlAs laser diode system (driver, temperature controller, and cooling mount) with a fiber optic delivery system (400 uM fiber) (all from Newport) was used in continuous wave mode. Laser dose was checked before each experiment with a power meter (Newport). Power density (irradiance, W/cm2) was varied to achieve various energy densities (fluence, J/cm2) for treating samples. For example, a spot size of 20, 30, or 50 mm for four wells in a 96-well plate, one 35-mm dish, or one 60-mm dish, respectively, was used by varying the target distance (beam divergence, 15°) and adjusting power (irradiance, W/cm2) assessed with a power meter. All treatments were performed as described earlier, and treatment time (5 min) was kept constant in all experiments. Owing to variations in laser output at very low power levels and attenuation by cell culture plastic and medium, a 10% dose variance was included in all in vitro experiments. Cell-free solution experiments were performed in black wells, whereas cell treatments were performed with a black background (card sheet) placed below the clear-bottom culture dishes or wells.In vivo assaysThe same laser unit described above (Newport) was used for in vivo (mouse and rat) experiments. This unit has a 400-?m fiber delivery system, and the end piece was placed directly on the exposed pulpal tissue and used at 0.01 W/cm2 for 5 min in continuous mode for a total dose of 3 J/cm2. The end piece was moved continuously in a smooth, uniform motion during treatments to ensure that there was no appreciable heating. Animals were treated only once and followed for 8 weeks (mice) or 12 weeks (rats).End Quote.So they used 810 nM laser out of a 400 um core diameter fiber, which suggests the Newport unit is capable of emitting quite a bit of raw power. Commercial use of diode arrays with 400 uM cores is typically reserved for driving other lasers as a pump. 400 uM is typically used foo 20 watt and up diodes. This is a big one, as in tens of Watts of CW optical output, possibly as much as 40-50 Watts.I did a little more digging and this is actually from Spectra Physics Lasers, which was Bought by Newport and Runs as a pretty much independent corporation, except for sales.My best guess as a laser professional is that this a fiber coupled pump (FCL) or a Fiber Array Pump (FAP) laser usually used for pumping a ND:YAG laser, hence the 810 nanometer nominal wavelength. The laser changes wavelength at 0.2 nm/'C, and they die if ran too hot, hence the TEC controller to keep the laser cold.Its coming out of a 400 um core fiber, which means its a reasonably uniform cone of light, diverging like crazy at 15 degrees full angle, as the fiber does not have a collimating lens on it. Its still a laser, it still focuses to a small diameter on the retina, and its still coherent, making it an eye hazard. In every sense of the word.810 is downright hazardous without laser safety glasses, as it penetrates to the cornea, is strongly adsorbed by the retina, looks like a very dim red as the eye just barely detects it. 50 watts of 810 pointed at a wall looks like a dim red LED where the spot hits, if done under controlled conditions, and this is one of the hazards we train for. We use black and white CCD cameras or Find-R-Scopes (image converter tube) to deal with visualizing these wavelengths.So while I can easily find the used FAP on Ebay, it needs a chiller and a high amperage constant current driver with no voltage spiking or current overshoot at all, as laser diodes and laser diode array modules are very sensitive beasts that run away without current limiting and soft start., A ballast resistor just isn't good enough to drive one. Even high power FAP arrays die if you sneeze. The right diode laser driver does not grow on trees and rarely shows up used. This is not a project for a beginner.The authors of the paper had 5-15K$ worth of laser gear.The laser power meter with a thermal head capable of accurately measuring this is 1500-2000$ new. Probably 500$ used. A couple of pairs of 175$ certfied safety glasses are needed. His campus Laser Safety Officer needs to know if he's doing this, as the specular reflection off the cell trays is an eye hazard and needs to be dealt with, by totally enclosing the experiment.You should find a competent laser technician, electrical engineer, or physicist to help you with this. Most large research campuses have a local laser user who can advise you.The laser you linked in the first post is the wrong wavelength at 950, and that matters in bio applications. 808-810 nm is a very common laser diode.A key phrase here is energy density, and unless you have an accurate laser power meter, you can really mess up this experiment.MY advice is based on 25 years of working with a wide array of lasers in industry, laser shows, and academia. I am a certified Laser Safety Officer. This laser is not in the toy class. It is a Class IV laser hazard under the international safety scheme. Which means its capable of starting a fire, and is an eye hazard even from a indirect, scattered, beam.You should be aware that this type of laser is hazardous. It requires users to have proper, professionally made, Eye Protection.Steve

author: Michael_P
author_rank: Contributor
timestamp: November 13, 2015, 05:18:57 pm
content: Quote from: LaserSteve on November 13, 2015, 03:52:17 pmThank you Steve for your professional and competent advice, it great that you are here.Safety google is worth every pennyIn case of IR laser safety and safety googles I think about not using it. But usingGOOGLE CARDBOARDand wireless camera, how do you think it is good idea?

author: LaserSteve
author_rank: Super Contributor
timestamp: November 13, 2015, 05:33:09 pm
content: Ah, are you joking about Google Cardboard? Really a used B&W CCTV camera with a C mount lens and a tripod is far more appropriate. We hook the cameras into a USB frame grabber on a PC. Most newer cell phones have good IR filters these days, and watching a monitor means you do NOT have your head down toward the laser.You need full wrap around glasses with an optical density (OD) of 6 at these powers.https://www.thorlabs.com/thorcat/6300/LG4-SpecSheet.pdfBe aware there are many Chinese sellers of hazardous, fake, false, laser safety glasses on Ebay, for 35-50$. You must get the real, tested, certified, legal, product.I seriously suggest you find the services of an experienced Laser Safety Officer.Steve

author: JimRemington
author_rank: Regular Contributor
timestamp: November 13, 2015, 07:40:11 pm
content: Beware of "safety googles".

author: IanB
author_rank: Super Contributor
timestamp: November 13, 2015, 09:56:42 pm
content: This thread is really scary.

author: DimitriP
author_rank: Super Contributor
timestamp: November 14, 2015, 12:01:05 am
content: Quote from: IanB on November 13, 2015, 09:56:42 pmI wonder what is going on in forums where surgeons hang out....

author: bson
author_rank: Unknown
timestamp: November 14, 2015, 03:40:18 am
content: Quote from: SteveLy on November 13, 2015, 09:04:37 amOr just diffuse it to 1cm^2 and you have 3J/cm^2.For 30J/cm^2, light up the target for 300s.

author: CatalinaWOW
author_rank: Super Contributor
timestamp: November 14, 2015, 05:45:01 am
content: After agreeing with all of the safety warnings, you can do the analysis safely. The required information is all in the data sheet and in your set-up.A. PowerB. Exit spot diameter.C. Beam divergence.D. Distance from exit aperture to the site you are illuminating.E. Illumination time.You use B., C. and D. to get the illuminated area, which combined with A. gives you power density. Add illumination time and you are there.I haven't read the source paper so don't know how accurately you need to do this in practice. If the tolerances are tight or the effects are non-linear you have to look into details like the power profile of the beam (in is never uniform, which is the first approximation used in the above instruction. The second approximation, which is where most stop is a gaussian profile.)If after doing the analysis you think you want to actually try something, please read all of the warnings again. Read about laser safety. Read about what it is like to find out you are blind in parts of your field of vision (maybe small parts, maybe not). Proceed with all of that in mind.

author: IanB
author_rank: Super Contributor
timestamp: November 14, 2015, 07:43:39 am
content: Quote from: CatalinaWOW on November 14, 2015, 05:45:01 amIn truth, the OP cannot do the analysis at all, let alone safely.The questions asked at the beginning are so elementary they could be answered by someone with a basic high school science education.If the questions needed to be asked it means the questioner does not even have the most elementary scientific understanding, which means in turn the questioner is not qualified to be working in this area.

author: Psi
author_rank: Super Contributor
timestamp: November 14, 2015, 07:51:27 am
content: This looks similar to the calculations required to do audience scanning at laser shows without damaging anyone's eyes.Could ask the guys over athttp://photonlexicon.com/forums/index.phpJust as long as you'renotdoing audience scanning they should be happy to help.

author: Michael_P
author_rank: Contributor
timestamp: November 14, 2015, 08:18:33 am
content: Quote from: bson on November 14, 2015, 03:40:18 amAccording to this I try to estimate best possible choiceand it look like low power 0.5 mW ir 808 nm laser pointer with spot diameter 2,5 mm will be suitable for 5 min in direct use.or 5 mW ir 808 nm laser pointer with spot diameter 8 mm will be suitable for 5 min in direct use.or 10 mW ir 808 nm laser pointer with spot diameter 12 mm will be suitable for 5 min in direct use.http://mpe.laserextreme.nl/http://omlc.org/education/ece532/class1/irradiance_flashlight.html

author: IanB
author_rank: Super Contributor
timestamp: November 14, 2015, 09:14:23 am
content: Quote from: Michael_P on November 14, 2015, 08:18:33 amCheck your calculations.A circle of diameter 2.5 mm is 0.25 cm.The area of the circle is therefore 3.14/4 * 0.25^2 = 0.05 cm2If the source is 5 mW the irradiance is 5/1000 / 0.05 = 0.1 W/cm2If this is applied for 5 minutes the total energy delivered will be 5 * 60 * 0.1 = 30 J/cm2

author: Michael_P
author_rank: Contributor
timestamp: November 14, 2015, 09:56:12 am
content: Quote from: IanB on November 14, 2015, 09:14:23 am

author: tggzzz
author_rank: Super Contributor
timestamp: November 14, 2015, 10:51:32 am
content: Quote from: IanB on November 14, 2015, 07:43:39 amThose statements are all correct, but I would add that trying to convert power to energy indicates a complete lack of understanding.Those statements should be repeated until the OP decides not to be a danger to himself and/or to innocent third parties that have the misfortune to be nearby. The Dunning-Kruger effect is unforgiving.I don't care what he does to his body; that's his affair. I do care about what he does to other people. If someone like the OP blinded me then I would have no alternative but to commit suicide, but would also do everything possible to ensure they do not pass their genes onto another generation.

author: CatalinaWOW
author_rank: Super Contributor
timestamp: November 14, 2015, 06:31:28 pm
content: OP does not know what he is talking about. Doesn't know enough to know what he doesn't know. Each of us was there once. Teaching, not derision is the appropriate corrective action. Warnings of the danger of proceeding before ignorance is ended are also appropriate.

author: LaserSteve
author_rank: Super Contributor
timestamp: November 14, 2015, 07:02:05 pm
content: I am the guy who posted the heavily redacted audience scanning stuff on Pl.This guy is going to irradiate something no matter what because a professor told him to. You have to understand graduate students. Sadly they will do whatever the professor wants, no matter what, in many cases.So, one, safety is the responsibility of his professor and the university. Two, we might be the only source of safety info he has.I'll post a link to the safety materials soon.Steve.

author: IanB
author_rank: Super Contributor
timestamp: November 14, 2015, 07:09:12 pm
content: Quote from: LaserSteve on November 14, 2015, 07:02:05 pmHave you considered the evident level of knowledge and maturity of the person in this thread? This is no university student. There is no professor. This is someone who presents every appearance of being a child of high school age.

author: tggzzz
author_rank: Super Contributor
timestamp: November 14, 2015, 07:12:25 pm
content: Quote from: CatalinaWOW on November 14, 2015, 06:31:28 pmTrue. Must also be tempered by our assessing all of:our ability to teachthe broad/complete subjectto a sufficient degreewithin the confines of this forumand for the OP to listen, understand and act appropriatelywhich is a pretty tall order.It would be more than a shame to do 50% of that, only for the other 50% to cause serious problems.

author: LaserSteve
author_rank: Super Contributor
timestamp: November 14, 2015, 07:30:41 pm
content: Michael, Do you understand that you could easily damage your eyes and the eyes of others in your lab by doing this experiment?

author: LaserSteve
author_rank: Super Contributor
timestamp: November 14, 2015, 07:36:42 pm
content: Ian,Sadly this is evident of the level of the English as a Second Language, graduate students that I deal with on a daily basis.For first year and second year bio students, and students who still in high school , but spend half a day at college, the level of performance we are seeing is common.Yeah, I know something is wrong, and I suspect Google Translate is not helping.Steve

author: IanB
author_rank: Super Contributor
timestamp: November 14, 2015, 07:45:30 pm
content: It is not about language and communication, it is about maturity and competence.This is someone who cannot correctly calculate the area of a circle, and when the mistake is pointed out responds by posting a silly animated GIF instead of correcting the mistake.

author: LaserSteve
author_rank: Super Contributor
timestamp: November 14, 2015, 07:49:24 pm
content: Ian B. I agree, something is very wrong.I'm not going to provide any other information until I know who he is and what he is working on. Except for Safety related materials. If he worked at the college I work at, I would have visited his prof and shut him down after the first few posts.I am, however, more and more shocked about the caliber of people admitted to grad school these days. I'm in contact with Campus Health and Safety several times a week trying to prevent basic accidents. The drive to score performance off of limited funding resources is massive. Few professors directly supervise their labs anymore, leaving that task to first year Postdoctoral researchers.However, if he really is a grad student, or one of the many high school students who attempt high level projects these days, he DOES need to understand that 808 nm Laser light is very dangerous.Steve

author: Michael_P
author_rank: Contributor
timestamp: November 14, 2015, 07:50:27 pm
content: Quote from: LaserSteve on November 14, 2015, 07:30:41 pmYes, I'm trying to slowly agree. In fact I don't have any experience with lasers.I know one person with dissection of the retina and his whole life is now upside down. Also this person don't know when and why he get this disease.

author: LaserSteve
author_rank: Super Contributor
timestamp: November 14, 2015, 08:09:06 pm
content: Michael, Would you care to tell us why you are asking for this information?Please be very specific about what you are doing, where you are doing it, and why?If you are doing this, it is very important that you complete a laser safety course for laboratory lasers conducted by a certified, trained, laser safety officer.With infrared laser light, you have NO blink reflex to protect you. An accident will happen and your retina WILL be damaged before you know it. Eye tissue does not heal well. Retinal burns, are for the most part, permanent and your vision will NEVER come backI'm going to link some things for you to read:https://www.osha.gov/dte/library/radiation/laser_rmcoeh_20021007/http://www.research.northwestern.edu/ors/forms/laser-safety-handbook.pdfSteve

author: Michael_P
author_rank: Contributor
timestamp: November 14, 2015, 08:26:00 pm
content: Quote from: LaserSteve on November 14, 2015, 08:09:06 pmOf course it is not a secret.I thinking about to try improve condition some of my teeth, and because some of them are to be removed, so I have nothing to lose.

author: LaserSteve
author_rank: Super Contributor
timestamp: November 14, 2015, 08:35:19 pm
content: Ok,800-900 nanometer laser light is about the worse thing you can expose your teeth and gums with in this case. Without proper technique and medicine, you will do more damage then you think, and it WILL be VERY painful.It will destroy any Dentin you have left on the surface of your teeth.Laser gum surgery is best left in the hands of Dental Surgeons. You should seek some form of professional help.I will Pray for you in my faith.This thread ends.Steve

author: tggzzz
author_rank: Super Contributor
timestamp: November 14, 2015, 08:43:05 pm
content: Quote from: Michael_P on November 14, 2015, 08:26:00 pm1: yes, you do have things to lose - your sight for a start2: this is good an example as any of why you should only answer questionsafterunderstandingwhythe question is being asked

author: DimitriP
author_rank: Super Contributor
timestamp: November 14, 2015, 09:11:00 pm
content: Quote from: tggzzz on November 14, 2015, 08:43:05 pmDidn't someone once say "With knowledge comes responsibility?And how do you stop the "whiners" ?Eventually someone "gives in" whether they should or not.And that's not "fixable".

author: Michael_P
author_rank: Contributor
timestamp: December 26, 2015, 10:02:28 am
content: Hi all,please look at this device "b-cure", is realizing exactly the same functionality as mentioned in this posthttp://www.gd-energies.com/

author: tggzzz
author_rank: Super Contributor
timestamp: December 26, 2015, 10:38:50 am
content: Quote from: Michael_P on December 26, 2015, 10:02:28 amSo what? That doesn't affect any of the points made.