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Three and Four Level Laser Schemes
We have said that the two level scheme is not generally feasible for laser action. There are two main reasons for this. The first reason is that the energy being used to pump the particles into the upper laser state has an equal probability of stimulating them back down. Thus it is not possible to get nore than half of the particles into the excited state. The three level scheme gets around this problem by first exciting the particles to an excited state higher in energy than the upper laser state.(See figure below) The particles then quickly decay down into the upper laser state. It is important for the pumped state to have a short lifetime for spontaneous emission compared to the upper laser state. The upper laser state should have as long a lifetime (for spontaneous emission) as possible, so that the particles live long enough to be stimulated and thus contribute to the gain.
The four level laser scheme goes one step further and also depopulates the lower laser level by a fast decay process.(see figure below) This greatly decreases the loss of laser photons (v2) by stimulated absorption processes since the particles in the lower laser level have a short life-time for spontaneous emission.
What else can I help you with?
Why two level pumping scheme is not suitable for laser action?
Actually two level scheme has serious difficulty. In two level upward (level 1 to 2)transition and downward transitions(2 to 1) occurs. In steady state, the population inversion not obtain. (population inversion Means the numbers of atom at level 2 is greater than level 1)
Why focusing of laser light is better than ordinary light?
Focusing laser light is more effective than ordinary light because laser light is coherent and monochromatic, allowing it to be tightly focused into a small beam with minimal divergence. This concentrated beam of laser light enables more precise control and greater intensity, making it ideal for applications such as surgery, cutting, and communications.
How far can a laser beam travel?
It depends on what colour it is, the type of laser it is, the output level, the quality of the optics and the media it's travelling through. In a perfect vacuum, they'll travel much longer than through atmosphere. For example, green lasers travel further than red or blue. Class 1 and 2 lasers have an output power level of <5mW. Class 3 can go up to 100mW. See related link.
Is potential energy negative in any physical system?
In some physical systems, potential energy can be negative. This occurs when the reference point for measuring potential energy is set at a higher level than the actual energy level of the system.
Why are laser beams more powerful than natural light?
Laser beams are more powerful than natural light because they are coherent, focused, and monochromatic. These characteristics allow laser beams to carry a high intensity of energy and be directed in a precise manner, making them more concentrated and powerful than the diffused and mixed wavelengths of natural light.
How is he-ne laser superior to ruby laser?
Helium neon laser is better than ruby laser or most of the four level lasers are better than three level lasers due to the following reasons: The laser output is continuous in the case of helium-neon laser. But it is in the form of pulse in the ruby laser. Ruby laser requires high power pumping source, whereas Helium-neon laser requires low power pumping source like electric discharge. Efficiency of helium-neon laser is more than ruby laser. The defects due to crystalline imperfections are also present in the ruby laser. But it is not so in the helium-neon laser.
Why a four level laser system is more efficient than three level system?
Achieving population inversion in a two-level atomis not very practical. Such a task would require a very strong pumping transition that would send any decaying atom back into its excited state. This would be similar to reversing the flow of water in a water fall. It can be done, but is very energy costly and inefficient. In a sense, the pumping transition would have to work against the lasing transition.
Can a two level system can be used for production of laser?
Yes, a two-level system can theoretically be used for laser production, but it is highly inefficient in practice. In a two-level system, the population inversion required for stimulated emission is difficult to achieve because any excitation of atoms or molecules to the upper energy level will quickly return to the ground state, leading to rapid thermalization rather than sustained lasing. Instead, most lasers utilize three-level or four-level systems, which facilitate a more effective population inversion and more efficient laser action.
Is laser printing better than inkjet for high volume printing?
Laser printers are better prepared to handle high-volume print jobs.Inkjets still do a better job than lasers of blending colors smoothly. Bottom line, laser printers are more cost effective.
Is the picture quality of a Laser TV better than normal HDTV?
A normal HDTV has better picture quality than a Laser TV. A laser TV basically looks like projector, whereas the normal HDTV has HD quality picture screen for your taste.
Which is better, electrolysis or laser hair removal?
Laser hair removal is much better than electrolysis. The reason is the result is more durable and if done right, it should be permanent.
What is the advantage to laser leveling?
Laser leveling, when properly done, provides a much more accurate means of measurement than typical "bubble" type levels. Laser levels can often be used hands-free and project/provide a level line much farther than a typical bubble level.
What is better than ink jet or ribbon in computer printers?
In my opinion, a laser printer is better than an inkjet or ribbon (dot matrix?) printer.
Are laxer jet cartridges better than inkjet?
"On almost every level, laser jet printer cartridges are superior to inkjet. They have longer life, they produce better images. The biggest drawback is their price, which can be 5 to 10 times greater."
What is the difference between ink jet and laser computer printers?
A laser printer makes a better quality print than a ink jet printer. An ink jet printer sprays the ink onto the paper and is sometimes blurry, whereas a laser printer is a pin point printing system.
How is a marking system better than a grading system?
marking system is better than grading system because for intell students
Is a class 3 laser better than a class 2?
It is not a question of Class 3 being "better" or "worse" than Class 2. Different classes are more suited than others for different applications. A Class 3 Laser is more powerful than a Class 2 laser, and so offers more opportunities to cause injury while being used.
