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Old 12-02-2009, 09:05 AM #1
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Unhappy Laser Lighter

Alright, I'm making a custom burning laser lighter, something I'm sure others have done, and I have a few questions.

Battery size is a major concern for me, and since I'm using a high powered infrared laser (1W, 808nm) it takes a lot of juice.

I've obtained a driver that can limit the current from 80mA-500mA.

I've got a little electronics background, but hardly any with lasers, so here's my question:

Will using higher voltage vs lower current have the same result as higher current and lower voltage?

I know I'm making a huge assumption, but here's my thought process:

P=VI right? So if the goal is a 1 watt laser, then I should be getting 1 watt either way. For example, 1 volt with 1 Amp would be 1 watt. So would 2 volts with 500mA. So would 4 volts with 250mA.

I would guess that using less current would probably be safer for the laser, but I don't know if I'll be sacrificing performance for it.

Will these changes with my power supply and driver affect the overall performance of my laser? I thought I remembered seeing something about current threshold for specific lasers, so I think I must have something wrong.

If someone can explain what I'm missing, that would be great. Thanks in advance.


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Old 12-02-2009, 09:12 AM #2
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Default Re: Laser Lighter

Sam's Laser FAQ: Welcome Page

there ya go that will answer everything.

With lasers 1 amp doesn't equal 1 watt in terms of light output, I'm sure some one could answer this better than me. (like sam) and the ***current*** is what dictates your output power, the lower the voltage, the shorter the life, the higher the voltage, the longer the life, but the you'll have more heat coming off, so If you to use a 12v battery or something use a bigger heatsink.
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Old 12-02-2009, 09:28 AM #3
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Default Re: Laser Lighter

Well, P = IV is always correct, but how much of that "P" is actually turned into light rather than heat? For example an ultrabright LED can produce as much light (visible) as a 60W incandescent light bulb in only 5 watts because the light bukb converts most of its energy into heat.

So you will need to look up the specs on the laser you're trying to drive. For example, some of the better 405nm laser diodes can convert current to light power (mA to mW) at roughly 1:1 ratios, but that's with a ~5V drop. The rest ends up being heat that you need to get rid of, lest you burn out the laser diode.

Other lasers are even less efficient. DPSS greens have high-powered IR lasers in them. These IR laser diodes lase at far lower voltage thresholds, so they don't use as much power. However, the IR is converted to visible green through special crystals and those crystals can only convert about 10% of the IR power into green light. So while the IR diodes are relatively efficient and can be driven to hundreds of mW, you'll only see 5mW of power from your green laser pointer, it'll eat up batteries to no end, and it'll generate a lot of heat in the process compared to a red or violet laser which is just a laser diode.

Read SAM's FAQ that was linked-to above. Very nice information on so many laser types.
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Old 12-03-2009, 06:02 PM #4
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Default Re: Laser Lighter

Also, you can't set both V and I to what you want running through your laser diode. You can only adjust one at a time and the other will be what the laser diode says it is going to be. Technically, you can only adjust voltage and current is the result, but with constant current drivers it's OK to think about it as setting a current, in which case you end up with a resultant voltage.

In other words, if you had a diode that ran at 500ma with 2V applied, and you wanted to run it at 1000ma with 1V, you'd have to change some other intrinsic property of the diode, in which case it would be a different diode. You can't just change the driver.
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