by Din » Fri Mar 25, 2016 1:46 pm
BobH wrote:"Pulsed" and "CW" refer to the excitation mechanism, not the output beam. The first CW lasers were RF excited.
Yes, I know. But, the pump radiation is not "continuous", it starts when you turn on the laser and stops when you turn it off. Also, the pump radiation is also quantised, since lasing itself is a quantum phenomenon, and so, it cannot be "continuous", since continuity of any physical phenomena is essentially classical.
The problem with such strict semantics is that it very quickly leads you down a lexicographic rabbit hole. I think it's just best to accept whatever the accepted verbiage is, rather than get overly pedantic. For example LASER is an acronym, not a word per se, except that it's accepted to use it as a word. If, however, acronyms are words in and of themselves, by virtue of usage, what about AIDS (Acquired Immuno Deficiency Syndrome) or that up-and-coming bio technique CRISPR (Clustered Regularly-Interspaced Short Palindromic Repeats)
This is what's playing out between those who call theses projection techniques "holography" and those (holographers) who think it's a "Pepper's Ghost". It's actually not a Pepper's Ghost because Pepper's Ghost refers to the reflection in a mirror of an actual physical object, not the projection of an image (or sequence of images) on a semi-transparent screen. If projection on a semi-transparent screen is the criteria for determining whether or not something is a "Pepper's Ghost", then every movie house in the world is showing a "Pepper's Ghost" since all media on which projections occur are semi-transparent to some extent. Alternatively, I can always back-project a scene onto a transparent screen while filming something in front of that screen, a la
https://www.youtube.com/watch?v=MDgH_Z8438w which is either a "Pepper's Ghost" from 1948, or just a back projection. I maintain, it's simply a back-projection.
Unfortunately, some "expert" in the holographic community declared that these were "Pepper's Ghost", and the entire holographic community followed suit, Pied Piper-like. All that's been accomplished is the replacement of one unknown word, hologram, by another unknown word, Pepper's Ghost, without defining or justifying either one (except of course, by an "expert"
!)
By the way, I used to get into a lot of these pedantic arguments when I was in college - it seemed the staple of any Physics department! - and then later during MENSA meetings - it seemed to be a staple of justifying another unknown quantity of "intelligence" whatever the heck that means!
[quote="BobH"]"Pulsed" and "CW" refer to the excitation mechanism, not the output beam. The first CW lasers were RF excited.[/quote]
Yes, I know. But, the pump radiation is not "continuous", it starts when you turn on the laser and stops when you turn it off. Also, the pump radiation is also quantised, since lasing itself is a quantum phenomenon, and so, it cannot be "continuous", since continuity of any physical phenomena is essentially classical.
The problem with such strict semantics is that it very quickly leads you down a lexicographic rabbit hole. I think it's just best to accept whatever the accepted verbiage is, rather than get overly pedantic. For example LASER is an acronym, not a word per se, except that it's accepted to use it as a word. If, however, acronyms are words in and of themselves, by virtue of usage, what about AIDS (Acquired Immuno Deficiency Syndrome) or that up-and-coming bio technique CRISPR (Clustered Regularly-Interspaced Short Palindromic Repeats)
This is what's playing out between those who call theses projection techniques "holography" and those (holographers) who think it's a "Pepper's Ghost". It's actually not a Pepper's Ghost because Pepper's Ghost refers to the reflection in a mirror of an actual physical object, not the projection of an image (or sequence of images) on a semi-transparent screen. If projection on a semi-transparent screen is the criteria for determining whether or not something is a "Pepper's Ghost", then every movie house in the world is showing a "Pepper's Ghost" since all media on which projections occur are semi-transparent to some extent. Alternatively, I can always back-project a scene onto a transparent screen while filming something in front of that screen, a la https://www.youtube.com/watch?v=MDgH_Z8438w which is either a "Pepper's Ghost" from 1948, or just a back projection. I maintain, it's simply a back-projection.
Unfortunately, some "expert" in the holographic community declared that these were "Pepper's Ghost", and the entire holographic community followed suit, Pied Piper-like. All that's been accomplished is the replacement of one unknown word, hologram, by another unknown word, Pepper's Ghost, without defining or justifying either one (except of course, by an "expert" :D !)
By the way, I used to get into a lot of these pedantic arguments when I was in college - it seemed the staple of any Physics department! - and then later during MENSA meetings - it seemed to be a staple of justifying another unknown quantity of "intelligence" whatever the heck that means!