Re: laser pulse vs trigger pulse in oscilloscope

Why Thank You! But one should not forget e.g. Phil Hobbs, he can be quite knowledgeable sometimes too :) :)

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John Devereux

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Presumably the Q-switch is being driven by periodic signal - you get a burst of RF, then no RF, then another burst of RF in a pattern that repeats itself exactly.

The claim is that the laser pulse should appear when the RF has been switched off.

If the period being displayed on the oscilliscope screen is long enough to include two or more bursts of RF on one channel, the laser pulse being displayed from the other channel will show up between the two bursts of RF - the precise time relationship depends on how the Q- switch works.

This doesn't sound like the sort of question that needs anybody really smart to answer it. If the OP had given some detail about the laser system and the Q-switch, there might be more that could be said by someone sufficiently well-informed (though not necessarily all that smart).

-- Bill Sloman, Nijmegen

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No, the claim is that the laser pulse should appear when the trailing
edge of the Q-switch trigger happens.

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Would you care to specify the repetition rate of the RF pulses? And the gap between the "disappearance" of the RF pulse and the appearance of the laser pulse? The only time I had much to do with an argon ion laser, the natural period of the laser - set by the cavity length - was 80MHz, so the pulses would have appeared every 12.5nsec, but there was a Q-switch which allowed you to pick out single pulses from time to time. The 12.5 nsec corresponds to the time it takes for light to travel 12.5 feet, and you can can get that kind of signal propagation around a lash-up without trying very hard.

Since he hasn't put any numbers on his expectations, he obviously hasn't started thinking about what is going on. Since you haven't either, your "later than it is supposed to" represents a comparable failure to engage what brain you've got.

Sure. You've obviously failed that first step, since you haven't noticed that there wasn't a lot to understand.

-- Bill Sloman, Nijmegen

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What does all that crap have to do with anything?

The man stated that he could see both the square trigger pulse from
the Q-switch and the pulse from the photodiode, but that the pulse
from the photodiode was appearing, not at the end of the trigger
pulse, as expected, but later on.

He then asked if anyone could explain why that was happening.

You then posted the following:

>> >If the period being displayed on the oscilliscope screen is long
>> >enough to include two or more bursts of RF on one channel, the laser
>> >pulse being displayed from the other channel will show up between the
>> >two bursts of RF - the precise time relationship depends on how the Q-
>> >switch works.

which indicates that you didn't understand that he had already stated
that he could see both pulses and was asking for the reason why they
weren't temporally aligned in the way he expected.

There's no greater irony here than the spectacle of you, an insecure self-conscious low-brow, desperately trying to acquire an ounce of self-respect through repeated unprovoked attacks on Sloman. It's not working. Maybe you should go back to calling yourself "Professional Circuit Designer" or even "El Presidente", but then those didn't work either did they?

Quoting Shakespeare is just another bad idea. You may achieve more success if you simply avoid trusting your instincts and, like George Constanza, just do the opposite!

-- Joe

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Bully for you. Why did we need to know that?

-- Bill Sloman, Nijmegen

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Your reading comprehension has let you down again. I was reconstructing his observations in terms that suited the dieas that I was trying to get across.

Don't be stupid. Nothing starts "immediately". there are always propagation delays around the system, and if you get them wrong the laser pulse can show up on the screen before the end of the RF pulse which was supposed to have triggered it - but only if you've got a looong cable frpm the RF pulse gnerator to the scope

Don't be silly. You've invested a great deal in the idea that "immediately" means a picosecond precise alignement, when if you took thirty seconds to think about what you were you'd realise that this is nonsense.

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That may be your opinion. As usual, it hasn't got mucy to do with reality.

Who else?

Dram on, nitwit.

The real irony is that you won't have noticed that _your_ little hand- cannon blew up in _your_ face, as Joe Legris has - very kindly - taken the trouble to point out.

-- Bill Sloman, Nijmegen

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If you think they're unprovoked, then you're cut from the same cloth
he is and no doubt share the same delusions.

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"Very kindly" because he can't see through your bullshit, feels sorry
for you, and doesn't realize that you're getting your just deserts.

That loon seems to be cut from the same cloth you are, so his opinions
and technical competence are just as suspect as yours are.

BTW, I think I made my point well enough to make it clear that you
didn't understand the OP's post the first time around, so I'll just
leave it at that and leave you free to play your silly little evasive
games.

John Fields does catch my typos and feed them back to me. These are real - if trivial - errors, which, granting his problems with sentence comprehension, are more salient for him than they are to the rest of us.

Unfortunately, because he can't comprehend complex sentences, he often thinks I've said something wrong when in fact I haven't and indulges himself in quixotic campaigns to get me to achknowledge my - non- existent - error.

Quite how these demeneted campaigns feed his self-respect is left as an exercise for the reader. I've got very little idea of how his mind might work, beyond "badly".

Google groups makes it easy.

Charming as ever.

-- Bill Sloman, Nijmegen

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You may like to see it that way. It's not a point of view that anybody else is likely to share.

When measured against John Field's infallible expertise. Which mostly seems to concern the care an feeding of the 555, which most people stopped using around 1980.

Which is to say that John Fields hasn't yet come to terms with the fact that he can't reliably parse complex sentences.

-- Bill Sloman, Nijmegen

Here is an example of Sloman's unprovoked attacks. To an obviously forged message, no less:

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Subject: Re: Any Smart DumbAss in here knows How to Increase the Capacitance of Electrolyte Capacitor? Date: Sun, 9 Mar 2008 04:42:53 -0700 (PDT) From: snipped-for-privacy@ieee.org Organization:

Newsgroups: sci.electronics.components, sci.electronics.design, sci.electronics.repair References: 1

If you weren't quite the ill-informed idiot that you are, you'd know that the dielectric in an electrolytic capacitor is formed by the electrolytic oxidation of the surface of the aluminium foil the forms the plates of the capacitor.

If you reverse bias the capacitor you can reverse this process, making the dielectric thinner ( and more likely to break down). Sadly, the reverse process is unlikely to thin the oxide layer to exactly the same extent at every point, so you run the risk of lowering the breakdown voltage faster than you increase the capacitance.

As cheap goes, this about a poor and investment of your time as you could make - short of slandering me in this user group which however does seem to give you some kind of demented satisfaction - but do try it. You won't enjoy the process at all, but does that worry me?

-- Bill Sloman, Nijmegen

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--
Politicians should only get paid if the budget is balanced, and there is
enough left over to pay them.

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Dr.Sloman.

I didn't see the OP's post as jargon. He obviously hadn't reflected on the significance of what he was seeing - otherwise he would have told us the time delay between the end of the RF pulse to the Q-switch and the appearance of the laser pulse - but his description of what was going on was explicit enough, if not particulalry detailed.

If you have had the experience with optical signals that you claim, you should be able to find out the propagation delay (from photo- cathode to anode) of a fast linear-focussed photomultiplier tube, which might well be relevant to the OP's query.

-- Bill Sloman, Nijmegen

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Actually, comparing you to Dr. Hobbs leads to the inescapable
conclusion that 'Mr.' suits you better.

Thank you so much for your kind reply (john field and bill specially . bye the way please be friend with each other ). Let me clear the question actually the pulse width of the square shape pulse(trigger pulse ) is 1 micro second. The laser pulse width is 100 nanoseconds and the time when the laser pulse starts is 3.7 micro second from the start of the square pulse. The trigger pulse switches the RF signal which is sent to the qswitch by Rf -driver on and off. In the qswitch we have a quartz crystal when the RF passes through the crystal it deflect the light and we don=92t have pulse. When the RF is off we have laser pulse. So the pulse should be built in the interval when we don=92t have RF it means in the 1 micro second interval. But it has a delay. I guess that delay is because of crystal in qswitch. When the Rf apply to fused silica crystal in qswitch it takes a time for rf to propagate through the crystal.th rf speed in crystal is around 109ns/mm . so for our qswitch that have a 60 mm crystal it takes 30=D7109 ns for rf pulse to reach in the middle of the crystal which is around 3 micro second . and it is reasonable. Is my guess right. Thank you again.

Thank you so much for your kind reply (john field and bill specially . bye the way please be friend with each other ). Let me clear the question actually the pulse width of the square shape pulse(trigger pulse ) is 1 micro second. The laser pulse width is 100 nanoseconds and the time when the laser pulse starts is 3.7 micro second from the start of the square pulse. The trigger pulse switches the RF signal which is sent to the qswitch by Rf -driver on and off. In the qswitch we have a quartz crystal when the RF passes through the crystal it deflect the light and we don=92t have pulse. When the RF is off we have laser pulse. So the pulse should be built in the interval when we don=92t have RF it means in the 1 micro second interval. But it has a delay. I guess that delay is because of crystal in qswitch. When the Rf apply to fused silica crystal in qswitch it takes a time for rf to propagate through the crystal.th rf speed in crystal is around 109ns/mm . so for our qswitch that have a 60 mm crystal it takes 30=D7109 ns for rf pulse to reach in the middle of the crystal which is around 3 micro second . and it is reasonable. Is my guess right. Thank you again.

sorry the crystal is fused silica not quartz

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The Q-switch works by using the RF excitation to turn the block of fused silica into a diffraction grating. The RF excitation propagates a mechanical - acoustic - wave through the block of silica creating alternating layers of compressed and rarefied silica which interact with the photons travelling through the silica as a diffraction grating

and - in more detail - on page 520

The acoustic wave is generated on one side of the block and absorbed on the other, so you would seem to be correct in associating your delay with propagation of the acoustic wave through the block.

There are going to be other propagation delays in your system, but 3.7 microseconds is a couple of orders of magnitude longer than anything that I was thinking of.

The PAL TV system relies on the propagation of a similar acoustic wave through a crystal to generate a 64 usec delay in a compact device

This is a Dutch thesis, but the bulk of the text is written in English.

-- Bill Sloman, Nijmegen