Lloyd wrote:LASER ACTION IN STELLAR ENVELOPES
* Thanks to Upriver for these papers. They seem to show what kinds of stars are likely to emit laser light. Does anyone have time to read these papers and see if they have anything else interesting to mention?
http://laserstars.org/pdf/1976Ap&SS..45...87V.pdf
Y. P. VARSHNI and C. S. LAM
Department of Physics, University of Ottawa, Canada
(Received 19 January, 1976)
Abstract. It is shown that in high-temperature stars in which high speed mass loss is occurring, the rapidly recombining plasma in the stellar envelope can act as an amplifying medium. Model calculations for laser action in He II λ4686, using the collisional-radiative model, are presented. Menzel's hypothesis of laser action in distended stellar atmospheres is shown to be fully substantiated. The relevance of these results in resolving the problem of intensity anomalies in the spectra of Wolf-Rayet stars is pointed out.
http://laserstars.org/pdf/1986Ap&SS.125..341V.pdf
Y. P. VARSHNI and R. M. NASSER
Department of Physics, Universiiy of Ottawa, Canada KIN6N5
(Received 26 March, 1986)
Abstract. Model calculations for laser action in He1 are carried out, when helium plasma is rapidly cooled by expansion. Results are presented for four transitions, two of which, 3^1 S+2^1 P^0 (λ7281) and 3^1 D -> 2^1 P^0 (λ6678), show strong population inversion. Available observational evidence for possible laser action in these two lines in Wolf-Rayet and emission-line stars is summarized and discussed.
I sure had some research fun with that.
But I guess I’m having some problems with this one so I’d appreciate anyone helping me understand what I’m missing. I took a look at those papers Lloyd has linked as well as the article(s) from Quantauniverse. I also took a look at what is apparently the website of Y.P. Varshni and J. Talbot called
Laser Stars.org.
The “
Summary” of the Laser Stars website has a graphic representation depicting the range of the ‘stellar envelope’ that qualifies as undergoing the “laser action” which is the specific term that is used in both the papers that Lloyd cited. That term, “laser action” seems to refer more so to the quantum mechanical interpretation of the way normal laser light is emitted by way of electrons undergoing stimulated or amplified emission of photons as a process.
One of the key principles, or criteria, that seem to be pointed to in Varshni’s theory is the occurrence of “population inversion” which means that:
Quantum mechanically speaking; the electrons, atoms, molecules of a given species and for a given system are normally at some “rest state”, or “ground state”. Under normal “at rest” circumstances a small random percentage, a very few, of the electrons - for said population of said species, may be in an excited state. One can take such system and “pump” it (stimulate) via some given means providing energy to the system. The “pumped” energy input would then result in an increase in the number of excited electrons in the species now exceeding the number of electrons at rest or in the “ground state”. When the number of electrons in the excited state exceeds the number of electrons in the “ground state” the subsequent nature of the population compared to the initial state of the species has become “inverted”; thus the term “population inversion”.
The reasoning occurs with relation to normal lasers positing that, likewise, in order to keep the necessary “population inversion” going so that your laser continuously emits light “a certain minimum power” must be provided as a “pump” i.e. energy must be continuously supplied to the system. The author of the following video lecture mentions electrically “pumping” the system and coverage of “population inversion” occurs a@ 8:30 secs.
Lecture 5 part 1 (Lasers, stimulated emission, population inversion)
Now, these energetically “pumped” electrons, atoms, or molecules can undergo “spontaneous emission” over time all by themselves or one can ‘enhance’ and/or induce emission via “recombination” (“ion with an electron with the simultaneous transfer of kinetic and binding energy to a third particle (usually another electron”, “
optical pumping” (injecting light aka “photon bombardment”)) etc. One of the papers aims to clear up some confusion with the naming conventions here:
6. Terminlogy
Finally we would like to add some remarks as regards the terminology. The phenomenon that we have discussed is known, more specifically, as supperradiance (Bloom, 1968) or supperradiant emission (Lengyel, 1971; siegman, 1971) in the literature of laser physics. Some authors (Allen and Peters, 1970; Allen, 1973) prefer the phrase amplified spontaneous emission. This helps to distinguish it from Dike’s supperradiance and avoid the semantic confusion surrounding the word supperradiance. We have, however, used the more general term laser action to describe the phenomenon, because it is better known to astrophysicists and because Menzel has used it in the same sense. Also, the term maser action in the contest of interstellar molecules is used in the same sense. –
Laser Action in Stellar Envelopes
Consider Population Inversion again because we need to be clear on what it means:
This scheme is capable of generating intense laser action and it is known as the plasma laser or recombination laser. (…) the recombination occurs preferentially into the upper excited states of the ion, which then decay by radiative and/or collisional cascade to the ground state. Within the cascade from the upper excited from the upper excited states, population inversions may form among the excited states depending on the relative transition probabilities. –
Laser Action in Stellar envelopes
So, that means lots more jucied -trons closer to the source outnumbering the sober -trons who've lost their buzz having 'collided' with the cold interstellar medium cop and rapidly cooled. So saying "laser action" seems more so a reference to the quantum mechanical processes or activities; not necessarily literal laser light or laser beams. This is where I'm having the problem needing help understanding. That, being said there is more of interest. The "Terminology" section of the above quoted paper states that
“In the astrophysical context, the term laser action actually means amplified spontaneous emission…”
With “amplified spontaneous emission”: a process where spontaneously emitted radiation (luminescence) is amplified”, the thing that is interesting is the “Gain Media”. Some of these are called “Gas Lasers” which means that they consist of “Noble Gasses” such as Helium-Neon Lasers and Argon i.e. plasma. Why is that a problem? – because generally speaking 99% of the observable universe is in the plasma state. Considering that as such it is also a problem because of the way that, in order to achieve consistent emission of photons by way of “population inversion”, the system must be “pumped”:
As the gain medium adds energy to the amplified light, it must itself receive some energy through a process called pumping, which
may typically involve electrical currents (electrical pumping) or some light inputs (→ optical pumping), typically at a wavelength which is shorter than the signal wavelength. –
Gain Media
And from the Laser Stars page on the inefficiency of
Photon Pumping one reads:
For this reason, most laboratory ion or atomic vapour lasers aren't photo-pumped with flashlamps or arclamps, they are instead excited by electron bombardment from a discharge.
So, instead of using photo-pumped methods for their vapor lasers the energy supplied for the continuation of “population inversion” is met with … ELECTRIC DISCHARGES.
Which then, by way of the Laser Stars link contained in that very sentence specifically leads to:
The Spectra of Gas Discharges
Hence, we’re basically right back to square one with turn of the century ‘electrical discharges in gasses’ (which we know to be (plasma), something that has been the bane of modern day astrophysics. I'm not saying that that is what Vashni et are saying but that certainly is a curious development as you read their website. I'm just pondering the implications of electrically pumped plasma lasers on our terrestrial sphere and the quantum mechanical interpretation of "population inversion" with excited electrons outnumbering lower energy electrons which excite the plasma into glow mode obviously from an astrophysical perspective as relates starlight from *some* stars. I didn't see anything in Vashni
et al that went that far but the implication is highly interesting don't you think?
However, the second technique, electrical pumping, is practical for lasers. If the laser medium is placed in an electron beam, the electrons can create a population inversion by transferring their energy to the atoms when they collide. Several types of high-power gas lasers are pumped this way. More common is another technique of electrical pumping; the direct discharge … an electric discharge is created in a tube containing the gaseous laser medium, similar to the discharge in a fluorescent lamp. A population inversion is created in the ions or atoms to the discharge when they absorb energy from the current. –
Introduction to Laser Technology: 7.5. Pumping Mechanisms
Precious. But it doesn't seem to infer lasers, or laser light, as normally perceived but more so an application of the interpretive quantum mechanical process.
"Our laws of force tend to be applied in the Newtonian sense in that for every action there is an equal reaction, and yet, in the real world, where many-body gravitational effects or electrodynamic actions prevail, we do not have every action paired with an equal reaction." — Harold Aspden
