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laser pulse vs trigger pulse in oscilloscope

Started by Ken S. Tucker October 25, 2010
This was posted in sci.physics.research.

On Oct 24, 3:12 pm, Abner Amber <amirg...@gmail.com> wrote:
> Dear Friends > I want to do some experiment in pulsed laser. I attached output of a > laser to one channel of oscilloscope via photodiode to see the shape > of the pulse. then I attach the one output of RF trigger of the > qswitch to the other channel of the oscilloscope to see the square > shape pulse of the Rf trigger till now everything is ok I can see > both pulses. But I can't interpret the relation between two pulses. To > my knowledge when we have RF we shouldn't have any laser pulse and > when the RF vanishes we should have laser pulse . it means that when > we compare two pulses in the oscilloscope as soon as the square shape > trigger pulse vanishes the laser pulse must be appear but it appears > later in the train of the pulse . what is the problem ? > Is the measuring equipment is poor or it has theoretical problem. > Thanks in advance
To start I'm reposting that to sci . electronics . design Regards Ken PS: One guys there is really smart, I don't know about the rest, of the others.
On Mon, 25 Oct 2010 08:36:51 -0700 (PDT), "Ken S. Tucker"
<dynamics@vianet.on.ca> wrote:

>This was posted in sci.physics.research. > >On Oct 24, 3:12 pm, Abner Amber <amirg...@gmail.com> wrote: >> Dear Friends >> I want to do some experiment in pulsed laser. I attached output of a >> laser to one channel of oscilloscope via photodiode to see the shape >> of the pulse. then I attach the one output of RF trigger of the >> qswitch to the other channel of the oscilloscope to see the square >> shape pulse of the Rf trigger till now everything is ok I can see >> both pulses. But I can't interpret the relation between two pulses. To >> my knowledge when we have RF we shouldn't have any laser pulse and >> when the RF vanishes we should have laser pulse . it means that when >> we compare two pulses in the oscilloscope as soon as the square shape >> trigger pulse vanishes the laser pulse must be appear but it appears >> later in the train of the pulse . what is the problem ? >> Is the measuring equipment is poor or it has theoretical problem. >> Thanks in advance > >To start I'm reposting that to >sci . electronics . design >Regards >Ken >PS: One guys there is really smart, I don't know about the rest, >of the others.
Post the oscilloscope shot somewhere, and maybe a better description of the optical setup. Is the q-switch an electro-acoustic modulator? John
"Ken S. Tucker" <dynamics@vianet.on.ca> writes:

> This was posted in sci.physics.research. > > On Oct 24, 3:12 pm, Abner Amber <amirg...@gmail.com> wrote: >> Dear Friends >> I want to do some experiment in pulsed laser. I attached output of a >> laser to one channel of oscilloscope via photodiode to see the shape >> of the pulse. then I attach the one output of RF trigger of the >> qswitch to the other channel of the oscilloscope to see the square >> shape pulse of the Rf trigger till now everything is ok I can see >> both pulses. But I can't interpret the relation between two pulses. To >> my knowledge when we have RF we shouldn't have any laser pulse and >> when the RF vanishes we should have laser pulse . it means that when >> we compare two pulses in the oscilloscope as soon as the square shape >> trigger pulse vanishes the laser pulse must be appear but it appears >> later in the train of the pulse . what is the problem ? >> Is the measuring equipment is poor or it has theoretical problem. >> Thanks in advance > > To start I'm reposting that to > sci . electronics . design > Regards > Ken > PS: One guys there is really smart, I don't know about the rest, > of the others.
Why Thank You! But one should not forget e.g. Phil Hobbs, he can be quite knowledgeable sometimes too :) :) -- John Devereux
On Oct 25, 5:36=A0pm, "Ken S. Tucker" <dynam...@vianet.on.ca> wrote:
> This was posted in sci.physics.research. > > On Oct 24, 3:12 pm, Abner Amber <amirg...@gmail.com> wrote: > > > Dear Friends > > =A0I want to do some experiment in pulsed laser. I attached output of a > > laser to one channel of oscilloscope via photodiode to see the shape > > of the pulse. then I attach the =A0one output of =A0RF trigger of the > > qswitch to the other channel of the oscilloscope =A0to see the =A0squar=
e
> > shape pulse =A0of the =A0Rf trigger till now everything is ok I can see > > both pulses. But I can't interpret the relation between two pulses. To > > my knowledge when we have RF we shouldn't have any laser pulse and > > when the RF vanishes we should have laser pulse . it means =A0 that whe=
n
> > we compare two pulses =A0in the oscilloscope as soon as the square shap=
e
> > trigger pulse vanishes the laser pulse must =A0be appear =A0but it appe=
ars
> > later in the train of the pulse . what is the problem ? > > Is the measuring equipment is poor or it has theoretical problem. > > Thanks in advance > > To start I'm reposting that to > sci . electronics . design > Regards > Ken > PS: One guys there is really smart, I don't know about the rest, > of the others.
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
On Oct 25, 9:02 am, John Devereux <j...@devereux.me.uk> wrote:
> "Ken S. Tucker" <dynam...@vianet.on.ca> writes: > > > > > This was posted in sci.physics.research. > > > On Oct 24, 3:12 pm, Abner Amber <amirg...@gmail.com> wrote: > >> Dear Friends > >> I want to do some experiment in pulsed laser. I attached output of a > >> laser to one channel of oscilloscope via photodiode to see the shape > >> of the pulse. then I attach the one output of RF trigger of the > >> qswitch to the other channel of the oscilloscope to see the square > >> shape pulse of the Rf trigger till now everything is ok I can see > >> both pulses. But I can't interpret the relation between two pulses. To > >> my knowledge when we have RF we shouldn't have any laser pulse and > >> when the RF vanishes we should have laser pulse . it means that when > >> we compare two pulses in the oscilloscope as soon as the square shape > >> trigger pulse vanishes the laser pulse must be appear but it appears > >> later in the train of the pulse . what is the problem ? > >> Is the measuring equipment is poor or it has theoretical problem. > >> Thanks in advance > > > To start I'm reposting that to > > sci . electronics . design > > Regards > > Ken > > PS: One guys there is really smart, I don't know about the rest, > > of the others. > > Why Thank You! But one should not forget e.g. Phil Hobbs, he can be > quite knowledgeable sometimes too :) :) > John Devereux
How did ya know I was thinking about a fella named John? This is a hallowed moment, 2 smart guys on a usenet group. Ken
On Mon, 25 Oct 2010 09:42:54 -0700 (PDT), Bill Sloman
<bill.sloman@ieee.org> wrote:

>On Oct 25, 5:36&#2013266080;pm, "Ken S. Tucker" <dynam...@vianet.on.ca> wrote: >> This was posted in sci.physics.research. >> >> On Oct 24, 3:12 pm, Abner Amber <amirg...@gmail.com> wrote: >> >> > Dear Friends >> > &#2013266080;I want to do some experiment in pulsed laser. I attached output of a >> > laser to one channel of oscilloscope via photodiode to see the shape >> > of the pulse. then I attach the &#2013266080;one output of &#2013266080;RF trigger of the >> > qswitch to the other channel of the oscilloscope &#2013266080;to see the &#2013266080;square >> > shape pulse &#2013266080;of the &#2013266080;Rf trigger till now everything is ok I can see >> > both pulses. But I can't interpret the relation between two pulses. To >> > my knowledge when we have RF we shouldn't have any laser pulse and >> > when the RF vanishes we should have laser pulse . it means &#2013266080; that when >> > we compare two pulses &#2013266080;in the oscilloscope as soon as the square shape >> > trigger pulse vanishes the laser pulse must &#2013266080;be appear &#2013266080;but it appears >> > later in the train of the pulse . what is the problem ? >> > Is the measuring equipment is poor or it has theoretical problem. >> > Thanks in advance >> >> To start I'm reposting that to >> sci . electronics . design >> Regards >> Ken >> PS: One guys there is really smart, I don't know about the rest, >> of the others. > >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.
--- No, the claim is that the laser pulse should appear when the trailing edge of the Q-switch trigger happens. ---
>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.
--- He has no trouble seeing both signals, his concern is with the laser pulse showing up later than it's supposed to. ---
>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).
--- First, one must learn to understand what he reads. --- JF
On Oct 25, 9:42 am, Bill Sloman <bill.slo...@ieee.org> wrote:
> On Oct 25, 5:36 pm, "Ken S. Tucker" <dynam...@vianet.on.ca> wrote: > > > > > This was posted in sci.physics.research. > > > On Oct 24, 3:12 pm, Abner Amber <amirg...@gmail.com> wrote: > > > > Dear Friends > > > I want to do some experiment in pulsed laser. I attached output of a > > > laser to one channel of oscilloscope via photodiode to see the shape > > > of the pulse. then I attach the one output of RF trigger of the > > > qswitch to the other channel of the oscilloscope to see the square > > > shape pulse of the Rf trigger till now everything is ok I can see > > > both pulses. But I can't interpret the relation between two pulses. To > > > my knowledge when we have RF we shouldn't have any laser pulse and > > > when the RF vanishes we should have laser pulse . it means that when > > > we compare two pulses in the oscilloscope as soon as the square shape > > > trigger pulse vanishes the laser pulse must be appear but it appears > > > later in the train of the pulse . what is the problem ? > > > Is the measuring equipment is poor or it has theoretical problem. > > > Thanks in advance > > > To start I'm reposting that to > > sci . electronics . design > > Regards > > Ken > > PS: One guys there is really smart, I don't know about the rest, > > of the others. > > 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
I single handidly invented the optical world! (had some help though). Back in 1980, we'd tweek a pulse down a fibre coil, maybe a km, watch the return on the scope, reckon dispersion, that's how the pulse base spread a bit, and from that 'ballpark' a max fequency, for that particular fibre media. Next thing we had to do was join and tap the fibre, cost was no object, except my pay. Obviously, I'm a bit rusty, so I posted this for those who might understand what the fella (OP from spr) is driving at. Thanks Ken
On Oct 25, 7:23=A0pm, John Fields <jfie...@austininstruments.com> wrote:
> On Mon, 25 Oct 2010 09:42:54 -0700 (PDT), Bill Sloman > > <bill.slo...@ieee.org> wrote: > >On Oct 25, 5:36=A0pm, "Ken S. Tucker" <dynam...@vianet.on.ca> wrote: > >> This was posted in sci.physics.research. > > >> On Oct 24, 3:12 pm, Abner Amber <amirg...@gmail.com> wrote: > > >> > Dear Friends > >> > =A0I want to do some experiment in pulsed laser. I attached output o=
f a
> >> > laser to one channel of oscilloscope via photodiode to see the shape > >> > of the pulse. then I attach the =A0one output of =A0RF trigger of th=
e
> >> > qswitch to the other channel of the oscilloscope =A0to see the =A0sq=
uare
> >> > shape pulse =A0of the =A0Rf trigger till now everything is ok I can =
see
> >> > both pulses. But I can't interpret the relation between two pulses. =
To
> >> > my knowledge when we have RF we shouldn't have any laser pulse and > >> > when the RF vanishes we should have laser pulse . it means =A0 that =
when
> >> > we compare two pulses =A0in the oscilloscope as soon as the square s=
hape
> >> > trigger pulse vanishes the laser pulse must =A0be appear =A0but it a=
ppears
> >> > later in the train of the pulse . what is the problem ? > >> > Is the measuring equipment is poor or it has theoretical problem. > >> > Thanks in advance > > >> To start I'm reposting that to > >> sci . electronics . design > >> Regards > >> Ken > >> PS: One guys there is really smart, I don't know about the rest, > >> of the others. > > >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. > > No, the claim is that the laser pulse should appear when the trailing > edge of the Q-switch trigger happens.
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.
> >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. > > He has no trouble seeing both signals, his concern is with the laser > pulse showing up later than it's supposed to.
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.
> >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). > > First, one must learn to understand what he reads.
Sure. You've obviously failed that first step, since you haven't noticed that there wasn't a lot to understand. -- Bill Sloman, Nijmegen
On Mon, 25 Oct 2010 16:22:22 -0700 (PDT), Bill Sloman
<bill.sloman@ieee.org> wrote:

>On Oct 25, 7:23&#2013266080;pm, John Fields <jfie...@austininstruments.com> wrote: >> On Mon, 25 Oct 2010 09:42:54 -0700 (PDT), Bill Sloman >> >> <bill.slo...@ieee.org> wrote: >> >On Oct 25, 5:36&#2013266080;pm, "Ken S. Tucker" <dynam...@vianet.on.ca> wrote: >> >> This was posted in sci.physics.research. >> >> >> On Oct 24, 3:12 pm, Abner Amber <amirg...@gmail.com> wrote: >> >> >> > Dear Friends >> >> > &#2013266080;I want to do some experiment in pulsed laser. I attached output of a >> >> > laser to one channel of oscilloscope via photodiode to see the shape >> >> > of the pulse. then I attach the &#2013266080;one output of &#2013266080;RF trigger of the >> >> > qswitch to the other channel of the oscilloscope &#2013266080;to see the &#2013266080;square >> >> > shape pulse &#2013266080;of the &#2013266080;Rf trigger till now everything is ok I can see >> >> > both pulses. But I can't interpret the relation between two pulses. To >> >> > my knowledge when we have RF we shouldn't have any laser pulse and >> >> > when the RF vanishes we should have laser pulse . it means &#2013266080; that when >> >> > we compare two pulses &#2013266080;in the oscilloscope as soon as the square shape >> >> > trigger pulse vanishes the laser pulse must &#2013266080;be appear &#2013266080;but it appears >> >> > later in the train of the pulse . what is the problem ? >> >> > Is the measuring equipment is poor or it has theoretical problem. >> >> > Thanks in advance >> >> >> To start I'm reposting that to >> >> sci . electronics . design >> >> Regards >> >> Ken >> >> PS: One guys there is really smart, I don't know about the rest, >> >> of the others. >> >> >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. >> >> No, the claim is that the laser pulse should appear when the trailing >> edge of the Q-switch trigger happens. > >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.
--- 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. ---
>> He has no trouble seeing both signals, his concern is with the laser >> pulse showing up later than it's supposed to. > >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.
--- Since the premise is that the laser pulse should start _immediately_ following the termination of the trigger pulse, there are no numbers required since the timing is inherent in the statement. Since you don't aseem to be able to understand a string of words all that well, here's a picture: -->|<--dT = 0 ____ TRIG____________| |_____________________ _ PD___________________| |___________________ As usual, when you're wrong, instead of just admitting it and getting on with your life you thrash around and hurl unwarranted invective in a vain attempt to muddy the water and move the finger that's pointing at you to point at something else. Cheater. ---
>> >This doesn't sound like the sort of question that needs anybody really >> >smart to answer it.
--- Perhaps not, but since you couldn't answer it it would have to be someone smarter than you. ---
>> >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).
--- Yeah, right, blame it on the OP. ---
>> First, one must learn to understand what he reads. > >Sure. You've obviously failed that first step, since you haven't >noticed that there wasn't a lot to understand.
--- Since you didn't even get what little there was, it seems you've hoisted yourself with your own petard in a deliciously ironic way. Or as Shakespeare had Hamlet say: "For 'tis the sport to have the enginer / Hoist with his owne petar" -- Hamlet III iv. --- JF
On Oct 26, 7:36=A0am, John Fields <jfie...@austininstruments.com> wrote:

> Since you didn't even get what little there was, it seems you've > hoisted yourself with your own petard in a deliciously ironic way. > > Or as Shakespeare had Hamlet say: > > "For 'tis the sport to have the enginer / Hoist with his owne > petar" -- Hamlet III iv. >
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