Scholieren.com forum - De helium neon laser

Ok, het is in het engels, en je zult het zonder al de diagrammen en grafieken moeten doen.

Ik kan het niet inscannen, want ik heb zo'n 1 waarbij je het papier er doorheen moet halen.(daarnaast heb ik problemen met mijn pc)

The Helium-Neon Gas Laser.

The fist succesful gas laser was put into operation by Javan, Bennet and Harriot in 1961. Since that time many different gas lasers, using gases of many kinds and mixtures, have been put into operation. Because it is inexpensive, unusually stable, and emits continuously, the He-Ne laser is widely used in optics and physics laboratories the world over.
And early form of He-Ne laser is shown in Fig. 30G (sowwy http://forum.scholieren.com/wink.gif) It is composed of a glass tube nearly 1 m long and contains helium at a pressure of approximately 1 torr and neon at a pressure of approximately 1/10 torr.(1 torr= 1 mmHg pressure.) The highly reflecting mirrors at the ends are precission-adjusted and made parralel to a high degree of accuracy.
A high voltage, such as that obtained from a step-up transformer or a Tesla coil, is supplied by means of sealed-in electrodes or by metal bands around the ends and middle.
Although there are 10 times as many helium atoms present in such a mixture as there are neon atoms, the orange color of the gaseous discharge is characteristic of neon atoms. The visible spectrum of helium contains strong lines in the red, yellow, green and blue, so the discharge appears as white light. The spectrum of neon, on the other hand, has so many strong lines in the orange and red and has so few in the green, blue and violet, that iss gaseous discharge appears to be orange-red[see fig 21H(e) and (ƒ)]. The neon spectrum also contains a large number of lines near infrared.
All the lower energy levels for helium and neon are given in Table 30A, and an energy level diagram for the same states is given in figure. 30H.
THe normal state of helium is a 1^So(otje omlaag) lever arising from the two valence electrons in 1s orbits. The excitation of either one of these electrons to the 2s orbit finds atom in a 1^So or a 3^S1 state, both quite metastable, since transitions to the normal state are forbidden by selection rules[see equation 29o].
Neon with Z = 10 has electrons in the normal state and is represented by the configuration 1s^2 2s^2 2p^6. When one of the six 2p electrons is excited tot the 3s, 3p, 3d, 4s, 4p, 4f, 5s etc., orbit, triplet and singlet energy levels arise. A subshel like 2p^5, lacking only one electron from a closed subshell, behaves though it were a subshell containing one 2p electron. The number and designations of the levels produced are therefore the same as for two electrons, all triplets and singlets.
As free electrons collide with helium atoms during the electric discharge, one of the two bound electrons may be excited to 2s orbits, i.e., tot the 3^S1 or 1^So states. Since downward transitions are forbidden by radiation rules, these are metastable states and the number of excited atoms increase. We therefore have optical pumping, out of the ground state 1^So and into the metastable states 3^S1 and 1^So.
When a metastable helium atom collids with a neon atom in its ground state, there is a high probability that the excitation energy will be transfered to the neon, raising it to one of the 1^P1 or 3^Po or 3^P2 levels of 2p^5 5s. The small excess energy is converted into kinetic energy of the colliding atoms.
In this process each helium atom returns to the ground state as each colliding neon atom is excited tot the upperlevel of corresponding energy. The propability of a neon atom being raised to the 2p^5 3s or 2p^5 3p levels by collision is extremely small because of the large energy mismatch. The collision transfer therefore selectively increases the population of the upperlevel neon.
Since selection rules permit transitions from these levels downward to the 10 levels of 2p^5 3p and these in turn to the 4 levels of 2p^5 3s, stimulated emissions can speed up the process of lasing. Lasing requires only that the 4s and 5s levels of neon be more densely populated than the 3p levels, Since 3p levels are only sparsely populated, lasing can be initiated without pumping a majority of the atoms out of the ground state.
Light waves emitted within the laser at wavelengths such as 6328, 11.177 and 11.523 Å will occasionally be omitted parallel to the tube axis. Bouncing back and forth between the end mirrors, these waves will stimulate emission of the same frequency from other excited neon atoms, and the initial wave with the stimulated wave will travel parallel to the axis. Most amplified radiation emerging from the ends of the He-Ne gas laser are in the near infrared region of the spectrum, between 10.000 and 35.000 Å. A photograph of an inexpensive laboratory type of He-Ne gas laser is shown in fig. 301. Methods for operating such lasers at one wavelength will be presented in Sec. 30.7.

Nou, dat was de He-Ne laser.

En wat zeggen we dan??? http://forum.scholieren.com/wink.gif http://forum.scholieren.com/biggrin.gif

Groetjes
Ben(die goedheid zelve is http://forum.scholieren.com/biggrin.gif http://forum.scholieren.com/tongue.gif