Calculating Green Output on Commercially Available Pointers

[Wolfman29]

Hey all. I am curious as to what the average efficiency is of a green DPSS system.

The reason I ask is because I measured the tailcap current to my driver to be roughly 550mA, and I am looking for a way to figure out, within reason, what kind of output this thing will be putting out of green. It's been stated to be >200mW by Rayfoss, but I don't totally trust that, especially because I am pretty sure it's not IR filtered. See this link: www.rayfoss.com.

The thing takes 3V, and it is drawing .55A, meaning the driver should be outputting anywhere around 1.4W, assuming a decent efficiency on that thing (should be pretty good because I am pretty sure it's a buck driver).

Next, assuming 1.4W of input to the 808nm LD, what kind of output can we be expecting? 700mW of power?

Based off of some research, I gather that an 808nm LD may have Vf of roughly 2V, and has a W/A ratio of about one, meaning about 50% efficiency on this diode (not that surprising, I hear 808nm LDs are the most efficient out there). So, it's reasonable to say that 1.4W of input to the 808nm LD is roughly equal to 700mW of output power on the LD.

So, then what is the efficiency of the Nd:YAG or Nd:YVO4? I read on Wikipedia (see here: Diode-pumped solid-state laser - Wikipedia, the free encyclopedia) that a normal DPSS system has an efficiency of 20%, meaning that I am *probably* getting something like 130-140mW of power (chose a lower range so it's more realistic).

Is this a rough method for measuring the GREEN output power?

The method I used here is described simply:

1) Find "Working voltage" of your laser, may be on spec sheet of the laser.
2) Measure amperage at tailcap with a fully charged battery.
3) Find total wattage input to driver by multiplying these two; reduce by 20% for a lower average of driver efficiency to get output wattage of driver.
4) Divide driver output wattage in half, roughly the efficiency of a 808nm LD.
5) Divide that number by five (rough efficiency of DPSS system).
6) That's your power!

Math terms:

Vw*At*.08 = Po_532nm
(Vw = working voltage of laser, At = tailcap measured current)

What do you guys think?

 

[anselm]

sounds about right to me......
IF the crystals are perfectly aligned.
IF duty cycle is respected in passively cooled units.

 

[Wolfman29]

Well, hopefully my crystals are aligned because my duty cycle is respected

 

[Low-Q]

Well, hopefully my crystals are aligned because my duty cycle is respected

If the uncollimated green dot is quite circular, the focus of the 808nm diode are good. I have tested different distances, and the green dot becomes oval and dimmed when the 808nm focus isn't right.

The size of the chrystal and the cooling capacity of the surrounding brass is also a factor to take into account. Bad cooling on a undersized chrystal will give a bright beam for a short while before it dimms to a weaker beam.

Vidar

 

[Wolfman29]

Yeah. Although, interestingly, about a second after I turn it on, it switches to a higher mode and then back to TEM00.

 

[Wolfman29]

So if my new DIY LPM is calibrated correctly (which I hope to God it isn't, otherwise both my blu-ray and my 445nm are sucky diodes), I am getting 133mW or so on my green laser (must be IR filtered). So that's a pretty accurate prediction I made, and it turned out pretty close if my LPM is right.

It started out pretty low though (at around 75mW), but after about 30s-1min of on-time, it started rising much more rapidly.

 

[lasersbee]

The only way you will be sure of the accuracy of your DIY LPM
is to check your LPM against a known calibrated LPM...

Jerry

 

[Wolfman29]

Of course. However I can get rough estimations by assuming values for multiple lasers and calibrating so all three are close.