erratic output from green laser pointer

The KTP frequency-doubling crystal may be more temperature-sensitive than is normal. This is a known characteristic, but perhaps the crystal is damaged or improperly aligned.

It may be normal. Green pointers have no temperature control and the entire process is tempterature critical. So as various parts warm up, the efficiency changes and this can be significant. Some are worse than others but they all vary. At least yours is brightest when it's warm.

Much more in the Laser FAQ.

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Mine has a hang up when warm. There is a dim then bright effect. I measured mine close to 5 mw as advertised. Many are a lot less. I thought mine was a gonner one time. The dot had a strange display and was very dim. After I removed the lint it was fine. I suppose there are a few variables that are going to cause effects.

greg

More info: I put the pointer into the refrigerator to cool for a few hours. At that temperature, the green output is barely visible projected onto a surface a half inch from the end of the pointer. I measured the current drawn from the batteries (remove end cap, insert ammeter into the circuit), and it was about 270 mA - almost the same as when it is operating at its brightest. Current appeared to be steady too.

I also had the beam hitting a surface at a shallow angle, and I could see that as the output changed in intensity, the intensity profile across the beam changed a great deal. Looks like one of the lasers (I don't know whether the 800 nm or the 1060 nm one) was changing its mode mixture quickly.

Once fully warmed up, it was back to normal.

From this, I'd conclude that the electrical side of the pointer is fine: no intermittent connections, and the laser diode current regulator is working. But at least one of the optical components is extremely temperature sensitive. It seems that if this particular pointer is going to be useful for pointing out things in the sky on cold clear nights, it will have to be kept in an inside pocket between uses.

Thanks to everyone who commented.

Dave

Orion is very good about standing behind their products. I would check with them even if you aren't the original purchaser. They might agree to exchange it for free.

"If it sits in a cool room (say 15 degrees C) for a while before I use it, the inital brightness of the beam appears quite low - perhaps 10% or less of maximum output. If I keep it turned on, it will flicker - becoming brighter then dimmer again multiple times, remaining at one brightness for a fraction of a second to a couple of seconds before abruptly changing brightness again. After about a minute of operation, it seems to come to full brightness and remain there, without flickering."

Laser pointer needs to be preheated before pointing if the room temperature is lower than 25 degrees C.Usually you can hold the laser in hands tightly about 30 seconds before pointing. The low temperature might cause unstable and lower power pointing in operation.

My condo is unheated, and is currently around 60 degrees F. (It has been as low as the high 40s during this winter.) All the laser-optical devices in my condo work properly -- including the DVD players in my computers, the DVD player in my bedroom, the BD player in the living room, and even a 25-year-old LV player.

The idea that a semiconductor laser has to be at a minimum temperature to work strikes me as decidedly odd. I'd expect the pointer to work if it were dropped in liquid nitrogen (at least until the battery froze).

"5mw Green laser warmup - highter power trick"

The common green laser pointer starts with an 808 nm IR laser, which excites a crystal to produce 1064 nm light, which then feeds a frequency doubling crystal to produce green 532 nm. Both crystals are temperature sensitive.

I have an early model green pointer which I use to boresight align mountain top dish antennas. My personal best is 5 miles, although others have gone much further with high power green lasers.

The instructions didn't say anything about warming up the laser, so my first attempt on a 6400 ft mountain top in Smog Angeles failed due to lack of light output. I eventually figured it out and now have a small battery operated hand heater and temp controller to keep around room temperature.

--
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Hint: In a DPSS laser assembly, it isn't the semiconductor component that is the heat-sensitive factor.

work

dropped

One of the printed circuit boards we build for a local customer is a heater board for their green diode laser. The board is .090 thick, with silver plated traces. 4 wire wound resistors surround a hole where the laser diode goes.

These are for a outside, cold winter, application.

Paul

Thanx to Jeff and Mike for the clarifications.

Greetings William, When the green laser pointers first cam out I got curious, bought one, and read a lot about how they work. They use two crystals to get green. First one crystal takes the 808 nm IR light in and lases at

1064 nm. Then this light goes into a KTP (potassium titanyl phosphate) crystal which doubles the frequency and so 532 nm laser light comes out. This second crystal is quite sensitive to temperature and won't put out as much light if too cold or too hot. Also, especially in the cheaper laser pointers, the IR laser draws a lot of current when it first is powered, and some type of cheap current limiter then cuts the current, so when the laser is cold pressing the button will result in a short duration bright beam which then dims rapidly. I don't remember if the laser also needs to be up to a certain temp to lase well. I do know that if they get too hot their life is shortened. I also know that repeatedly pressing the button on a cold laser with a couple seconds between pushes will warm the laser faster and thus be brighter than just pressing and holding the button down. Another fault of some of the cheap pointers is the chrome plating on the threads of the battery compartment. The chrome plating develops a high resistance oxide coating very fast. So if the laser is dim after sitting around a few days unscrewing and screwing back together the two halves of the laser will abrade away this coating and the laser will be much brighter. I discovered this on pointers I had bought and I'm sure I'm not alone. Eric

operation.

Mine goes dim when warm, after trying to use it or a while.

Greg