Hi:
I am trying to measure the shot-to-shot energy stability of a pulsed optical parametric oscillator. It produces 8ns, 125mJ pulses of 460nm light, which I measure with either a 1ns photodiode, or a pyroelectric "joulemeter" sensor which produces a several microsecond pulse whose peak amplitude is proportional to the laser energy.
In the PD case, I integrate the instantaneous power vs. time on a scope, then measure the peak-peak amplitude of the integral with statistics to get energy. In the pyro sensor case, I simply measure the amplitude with statistics.
My Agilent MSO7054 scope can do this, but has some deficiencies:
- It doesn't automatically compute relative standard deviation which is the important thing, so I have to type in the std.dev. / mean every time with my calculator to see the effect. Since the OPO average energy might change along with the std. deviation when a change is made, I can't just look at the absolute std. dev.. I need relative std. deviation.
- It does accumulating rather than moving average stats., so I have to press "reset statistics" to start a new accumulation every time I make a change to the optics to see what the effect was.
- Ideally I'd like a trend plot of the relative standard deviation as well.
I've been considering three other scope models, the Agilent 9000 series, Tek DPO7000, and Tek MSO4000.
Today I evaluated the Tek MSO4054 and Agilent 9000. The Tek can do a moving average statistic which is an improvement. But still no relative standard deviation. It doesn't allow one to write arbitrary expressions using the statistical measurements, only the built-in waveform measures, so there is no way to compute rel. std. dev. with its math expression feature.
The Agilent 9000 (I forget precisely which model) also had no way to compute rel. std. dev., and I couldn't figure out whether it was doing moving ave. or accumulating stats. I didn't spend a whole lot of time with it after being sure it wasn't an improvement over the MSO4054.
Tomorrow I will see a Tek DPO7000, but after studying the manual tonight, I'm convinced that it will also not be able to write math expressions using the stats. So I expect I will discover that it too can't do what I want.
A pal at work recently bought a LeCroy 104MXi-A which costs less, has more BW, more memory, and faster sampling than the 500MHz Tek and Agilent scopes that are about the $ limit my boss can handle.
He told me it can basically do everything I want! I will call LeCroy tomorrow and request a demo. They lent him one for 5 days to eval.
But many people swear "LeCroy sucks." Actually, I used one in college. It had statistical calculations at a time when this was unheard of. It made easy work of some physics research that we were doing on organic photo-refractive polymers.
So while the LeCroy's might not be the best electronic debugging tools (slower waveform update rate under some circumstances) for finding glitches, etc., they do seem to be superior laboratory data acquisition and analysis platforms, for a similar price class to Tek and Agilent.
I will hopefully discover the real truth in a few days.
Any comments will be appreciated!
Good day!