Why you need to research before buying parts...
I meant to build a laser rangefinder (see paper that drove this idea here).
I'd like to get away from having to frequency adjust the laser, so I run across an Erbium rod for $10. Even if it's too damaged to work, I'm not out much. Now, my research into Erbium is that it's used in eye-safe lasers with a wavelength of 1.5um. Wonderful. It's on order and shipped as I type this.
Unfortunately, there's two types of Erbium doped rods. One is Erbium:Glass, with a pinkish color. This does the 1.5um lasing. Then there's Erbium:YAG. More expensive, it does 2.9um (half the frequency). It's greenish. See the link above? Yep, it's greenish. Unless they have a different color, I think I was shot down before I even started. There goes my "simple laser pulse". I also ordered several spare supposedly laser optics and several displosable flash units. Guess that means I'll have $20 or so in hardware sitting in my parts boxes for a while.
Now, depending on if the lasing rod lucks out in damage, I COULD try and get the rest of the parts, but I suspect it'd be cheaper for me to track down an Er:Glass rod than to get the frequency doubling crystal (KTP or KTA perhaps? I need a good laser handbook).