Mode shift?

[Moptsp]

Well, I know it's normal for DPSS lasers to mode shift as it's just one of those things that go along with it. But what is acceptable and what isn't, I'm not too sure. Here is a video of my RPL-260. It's of the spot with the laser being about ~25ft back. The camera has a red filter to help clarify the spot. When you see the whole video dim and brighten, this is just the camera trying to adjust, it's not the laser bouncing in output. Just pay attention to the shape, and watch closely at about 0.06.

[Link rather than embed as the forum parser is acting weird right now]
YouTube - ‪Possible Mode Shift?‬‎

I was talking to Jack a week or two back about this, he said it's normal for the shape of the beam to change a bit as the temperature changes, but he said not for it to mode hop, I believe. Would this be mode hopping or more on a normal acceptable level? I don't notice it really when using the laser for burning or other close range applications. Though I have noticed once when shining the laser at very distant trees the spot looks to be more oval to rectangle like than circular.

I also have to note that sometimes it doesn't really do this and the spot looks real perdee. But as you see here, some times it does do weird things. So no, it's not a constant hopping machine, but it can do it enough that I catch it like this.

Side Note:
This was on the adjustable tail cap at level 8.

 

[Assainator75]

Well 'technically' lower quality DPSS lasers will tend to be modehopping quite a lot (usually TEM01 to TEM03). That's just how they work... even high quaility DPSS lasers may modehop during warmup or operating at an inefficient temperature. From what I've read and observed myself, DPSS will most definetely modehop on unstable power sources such as low batteries. Check to see if your battery is fully charged.

However, on a quality unit such as an RPL with superior heatsinking, there really shouldn't be much reason why it would be modehopping. Btw... modehopping is pretty clear if you are wearing goggles. If it's not one "dot" and looks like it's been split... then it's a mode shift. If it's not exactly perfect TEM00, but looks to be near circular (slightly oval) ... then it's acceptable. From the video... it 'appears' to look like TEM02 or 03 as you pointed out.

However, I thought I read about how the max setting on the tailcap isn't always 'max output'. If you had an LPM, it should be adjusted to the point where your laser is most efficient and no longer increasing in output otherwise modehops may occur due to crystals being oversaturated (power output can also drop due to inefficiency). Honestly I don't know your laser, but it could be best at setting 8. (every laser is different - Jack usually sets it at an optimal position though )

Just saying... quality DPSS lasers should NOT modehop when operated at optimal settings otherwise it may be a crystal misalignment/defects. Usually it's just the temperature (warmups & extreme temperatures), or the battery.

 

[Moptsp]

I was running it at level 8, the optimum current level that Jack stated. I do notice it seems to do it more on a lower battery. I guess I will have to perform this test on a full one.

Thanks man.