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Would it be a gross oversimplification to think of the 2p effect as
analogous to rogue waves on the sea? Those occur when multiple waves
temporarily match vector and frequency and their amplitudes add together.
The sea wave analogy may help to explain why 2p is so nonlinear, as a
DeepSee or Cameleon always produces a range of wavelengths yet two waves
need to precisely match in space, vector and wavelength in order to go
rogue.
I know that quantum mechanics has a lot more going on than sea waves
sloshing around a Newtonian world and tipping the Poseidon over, but I
wonder how deep this discussion needs to go.
When teaching (elementary) FRET I always talk about what physicists
understand but practitioners do not necessarily need to memorize
themselves. e.g., deriving the sixth power law or explaining what exactly
gets transferredč if not a photon. And if it is not a photon they why
does polarization still work? What did space look like before the big
bang? And so on down a hole chasing a rabbit with a pocket watch. Note
that I am not trying to sidetrack the thread, I just want to suggest that
we specify how far down we want-slash-need to go. Allowing of course that
folks have different needs.
Cheers,
TF
Timothy Feinstein, Ph.D. | Confocal Manager
333 Bostwick Ave., N.E., Grand Rapids, Michigan 49503
Phone: 616-234-5819 | Email: [log in to unmask]
On 4/7/14, 10:20 AM, "Smith, Benjamin E." <[log in to unmask]> wrote:
>*****
>To join, leave or search the confocal microscopy listserv, go to:
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>8ogAJZQ&u=http%3a%2f%2flists%2eumn%2eedu%2fcgi-bin%2fwa%3fA0%3dconfocalmic
>roscopy
>Post images on
>http://scanmail.trustwave.com/?c=129&d=zbTC0zpLoupwLE6t2HWM55ZZjbebwN5SDBZ
>98ApdNQ&u=http%3a%2f%2fwww%2eimgur%2ecom and include the link in your
>posting.
>*****
>
>I find Paul Falstad's simulation helpful in visualizing energy state
>transitions. The model shows how quantum state transitions can be
>thought of as continuous:
>http://scanmail.trustwave.com/?c=129&d=zbTC0zpLoupwLE6t2HWM55ZZjbebwN5SDEw
>s8g8KPA&u=http%3a%2f%2fwww%2efalstad%2ecom%2fqmatomrad%2f
>
>Since virtual states are unmeasurable, two photon excitation can be
>thought of as a coupling process between the two photons and the induced
>dipole:
>http://scanmail.trustwave.com/?c=129&d=zbTC0zpLoupwLE6t2HWM55ZZjbebwN5SDBV
>4oQwLPA&u=http%3a%2f%2fresearchspace%2eauckland%2eac%2enz%2fbitstream%2f22
>92%2f433%2f2%2f02whole%2epdf
>
>The way I imagine it is as two separate yet simultaneous steps. The
>first photon induces a dipole oscillation to a virtual state.
>Effectively simultaneously, a second photon also induces a further dipole
>oscillation kicking the dipole all the way up to an observable energy
>state. The key is that both photons need to act on the molecule
>simultaneously, or the "virtual state" dipole disappears before the next
>photon can induce any further energy.
>
>An analogy would be trying to roll a boulder up onto a log. Two people
>of equal strength set about the task of rolling over a boulder up onto a
>log. Both people have enough strength to get the boulder to rock back
>and forth, but neither can get it up onto the log by themselves. If one
>person tries to move the boulder, the boulder will rock back and forth,
>but the moment they stop, the boulder will come to a rest as though
>nothing had been done to it. The rocking boulder can be thought of as a
>virtual state, where the boulder will drop back to its "ground state" the
>moment someone stops rocking it.
>
>However, two people decide to work together (this is like the coupling
>model). They time their rocking together, and by doubling their effort,
>they are able to roll the boulder all the way over to the meta-stable
>state of being on top of the log. The boulder will then reside atop the
>log for some time before dropping back down, emitting energy equal to
>both people's contribution, minus some energy due to friction an noise
>(just like two-photon emission).
>
>The reason why two photon excitation needs to be thought of as a coupling
>process, is let's think about a third scenario. Person A starts to rock
>the boulder. Then, person A lets go of the boulder and then person B
>immediately continues rocking the boulder. Then end result of this
>effort would be a rocking boulder, however, since A and B aren't acting
>on the boulder at the same time, they won't ever be able to transition
>the boulder up onto the log.
>
>Finally, let's imagine a world where the boulder can only be measured
>based on it's height of the ground. Rocking neither raises nor lowers
>the boulder, so it wouldn't be an observable state. However, we know
>that the boulder would have had to have been rocked back and forth to get
>it up onto the log, so while we can't observe it, we know it must exist.
>
>Hope this helps,
> Ben Smith
>
>Benjamin E. Smith, Ph.D.
>Samuel Roberts Noble Microscopy Laboratory
>Research Scientist II
>University of Oklahoma
>Norman, OK 73019
>E-mail: [log in to unmask]
>Voice 405-325-4391
>FAX 405-325-7619
>http://scanmail.trustwave.com/?c=129&d=zbTC0zpLoupwLE6t2HWM55ZZjbebwN5SDBF
>59QAMNg&u=http%3a%2f%2fwww%2emicroscopy%2eou%2eedu%2f
>
>
>________________________________________
>From: Confocal Microscopy List [[log in to unmask]] on
>behalf of John Oreopoulos [[log in to unmask]]
>Sent: Monday, April 07, 2014 8:06 AM
>To: [log in to unmask]
>Subject: Re: two-photon absorption
>
>*****
>To join, leave or search the confocal microscopy listserv, go to:
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>roscopy
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>http://scanmail.trustwave.com/?c=129&d=zbTC0zpLoupwLE6t2HWM55ZZjbebwN5SDBZ
>98ApdNQ&u=http%3a%2f%2fwww%2eimgur%2ecom and include the link in your
>posting.
>*****
>
>If you're into quantum mechanical calculations, there is actually a
>fairly good derivation of the 2-photon process here at this link:
>
>http://scanmail.trustwave.com/?c=129&d=zbTC0zpLoupwLE6t2HWM55ZZjbebwN5SDEE
>roVoOPA&u=http%3a%2f%2fchemwiki%2eucdavis%2eedu%2fPhysical%5fChemistry%2fS
>pectroscopy%2fElectronic%5fSpectroscopy%2fTwo-photon%5fabsorption
>
>Cheers,
>
>
>John Oreopoulos
>Staff Scientist
>Spectral Applied Research Inc.
>A Division of Andor Technology
>Richmond Hill, Ontario
>Canada
>http://scanmail.trustwave.com/?c=129&d=zbTC0zpLoupwLE6t2HWM55ZZjbebwN5SDEx
>5pVtaZw&u=http%3a%2f%2fwww%2espectral%2eca
>
>On 2014-04-07, at 8:35 AM, Chen, De (NIH/NCI) [C] wrote:
>
>> *****
>> To join, leave or search the confocal microscopy listserv, go to:
>>
>>http://scanmail.trustwave.com/?c=129&d=zbTC0zpLoupwLE6t2HWM55ZZjbebwN5SDE
>>N8ogAJZQ&u=http%3a%2f%2flists%2eumn%2eedu%2fcgi-bin%2fwa%3fA0%3dconfocalm
>>icroscopy
>> Post images on
>>http://scanmail.trustwave.com/?c=129&d=zbTC0zpLoupwLE6t2HWM55ZZjbebwN5SDB
>>Z98ApdNQ&u=http%3a%2f%2fwww%2eimgur%2ecom and include the link in your
>>posting.
>> *****
>>
>> To my knowledge, one photon excitation is linear optical process
>>(dipole excitation, which is proportional to light intensity I), while
>>two photon excitation is nonlinear (quadrupole excitation, proportional
>>to I^2) ; In two photon absorption, an intermittent energy level close
>>to one photon resonance will enhance the two photon excitation depending
>>on the offset from the resonance energy level. Two photon excitation
>>requires high laser power to excite. Short pulsed laser can provide the
>>required high enough peak power to excite with two photon. Forbidden in
>>dipole excitation is allowed in quadrupole excitation.
>>
>> Reference:
>> "The Principles of Nonlinear Optics" Y. R. Shen, 1984 | ISBN-10:
>>0471889989 | ISBN-13: 9780471889984
>>
>> ________________________________________
>> From: Marcus Knopp [[log in to unmask]]
>> Sent: Monday, April 07, 2014 5:53 AM
>> To: [log in to unmask]
>> Subject: Re: two-photon absorption
>>
>> *****
>> To join, leave or search the confocal microscopy listserv, go to:
>>
>>http://scanmail.trustwave.com/?c=129&d=zbTC0zpLoupwLE6t2HWM55ZZjbebwN5SDE
>>N8ogAJZQ&u=http%3a%2f%2flists%2eumn%2eedu%2fcgi-bin%2fwa%3fA0%3dconfocalm
>>icroscopy
>> Post images on
>>http://scanmail.trustwave.com/?c=129&d=zbTC0zpLoupwLE6t2HWM55ZZjbebwN5SDB
>>Z98ApdNQ&u=http%3a%2f%2fwww%2eimgur%2ecom and include the link in your
>>posting.
>> *****
>>
>> As far as I know, the effect, on the one hand, depends on the timing of
>>the subsequent photons to be absorbed. They have to reach a fluorophore
>>within a short time interval of sub-femtoseconds to a few femtoseconds,
>>i.e. quasi simultaneously. On the other hand, it depends on the symmetry
>>of a fluorophore, which, I think, determines the transition matrix
>>between energy levels. Then it all comes down to whether a transition is
>>allowed or not by the selection rules, which constrain transition for
>>example by the need to conserve an electron's angular momentum. What
>>exactly is going on, I don't know (does anybody?), but one
>>interpretation is indeed, that the first photon induces a transition
>>from the ground state to a virtual excited state at an intermediate
>>energy level (what's wrong with that? It's just a model). This is
>>thought to be close to a real state that can be occupied according to
>>the selection rules. The second photon carries the system from the
>>virtual state to the final state, that originally might have been
>>forbidden.
>>
>> Best,
>> Marcus
>>
>>
>> -----Original Message-----
>> From: Confocal Microscopy List
>>[mailto:[log in to unmask]] On Behalf Of Martin Wessendorf
>> Sent: Monday, April 07, 2014 4:24 AM
>> To: [log in to unmask]
>> Subject: two-photon absorption
>>
>> *****
>> To join, leave or search the confocal microscopy listserv, go to:
>>
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>>icroscopy
>> Post images on
>>http://scanmail.trustwave.com/?c=129&d=zrTC0wJ3Btfng3o6Ki8VL3Twis07aGkKBN
>>munjcFqA&u=http%3a%2f%2fwww%2eimgur%2ecom and include the link in your
>>posting.
>> *****
>>
>> Dear List--
>>
>> Is there a physicist out there who can offer an intuitive explanation
>>of how 2-photon absorption occurs? I expect we all know that it isn't
>>that there isn't any half-excited state that allows one photon to boost
>>an electron half-way to the excited state, and the next photon to finish
>>the job. My sense is that it has to do with time-energy uncertainty (a
>>la Heisenberg) but my quantum mechanics is elementary-school level.
>>
>> Thanks!
>>
>> Martin Wessendorf
>>
>> --
>> Martin Wessendorf, Ph.D. office: (612) 626-0145
>> Assoc Prof, Dept Neuroscience lab: (612) 624-2991
>> University of Minnesota Preferred FAX: (612) 624-8118
>> 6-145 Jackson Hall, 321 Church St. SE Dept Fax: (612) 626-5009
>> Minneapolis, MN 55455 e-mail: [log in to unmask]
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