Can anyone direct me to a data sheet for the type of laser diode (or laser diode module) used in the really cheap laser pointers (the ones with < 1 mW output, no fancy current regulator or power output feedback...just a series current limiting resistor) ? My search efforts have not managed to find one.
Steve
You might try Lasermate, motto "The Friend of Laser."
John
Thanks, John. I wasn't aware of that company....but still, as far as I can tell, their lowest power diode is 5 mW and their modules all use feedback power control.
Steve
Yes, I have found many like this...but the type of module I am asking about does not use the power monitor for feedback.
something.
Actually it is more the lack of the use of the output monitor that scares me ! I am trying to understand how the manufacturers of such laser pointers get away with it, what the temperature constraints might be, etc.
It has just occurred to me that the cheap pointers may just be LABELLED as "< 1 mW" for the purpose of fooling customers and customs inspectors but may actually contain 5 mW diodes running at some unknown power that may or may not be under a milliwatt depending on temperature, state of batteries, etc. If this is the case then perhaps a typical 5 mW diode data sheet could be instructive.
Steve
Give them a call. They can usually find what you need.
John
something.
We use VCSEL lasers, about 1 mW fiber-coupled, with constant-current drive, and they work fine. We switch them on/off in a few hundred picoseconds, and leave them on/off for indefinite times, so feedback isn't feasible for us.
John
I direct you to this:
Hmmm- hopefully your application skills are better...if the output monitor scares you, then maybe you should take up stamp collecting or something.
Do the cheap laser pointers use photodiode feedback? They seem to work fine.
John
One model (which I acquired for the princely sum of CDN $1.95) consists of just three 1.5V cells, a switch, a 68 ohm resistor and a laser diode (all in series of course), as far as I can tell. I have wondered about holding in my hand for a few minutes and seeing if it goes out and then leaving it outside for an hour and seeing if it goes out....permanently ! Or has someone in China figured out how to make a less-temperature-sensitive diode ?
Steve
One model (which I acquired for the princely sum of CDN $1.95) consists of just three 1.5V cells, a switch, a 68 ohm resistor and a laser diode (all in series of course), as far as I can tell. I have wondered about holding in my hand for a few minutes and seeing if it goes out and then leaving it outside for an hour and seeing if it goes out....permanently ! Or has someone in China figured out how to make a less-temperature-sensitive diode ?
Steve
You can do this because with VCSELs the threshold current tends to be a much smaller fraction of the operating current. With visible laser diodes (VLDs) this is not generally the case. E.g. the threshold at
25'C might be 20mA, with 30mA destroying the device. But the threshold at 70'C might be 50mA...-- John Devereux
Apparently not, according to Steve.
The VLD's I have used increase the threshold current with temperature. So if you set the current to give the nominal output at
20'C, then they would just get dim or go out at high temperatures (or as they self-heat). But if it got too cold, then you might be in trouble!-- John Devereux
ElectronDepot website is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.