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Traction is the laser linewidth and frequency to the laser characteristics. Line width is due to the presence of spontaneous emission, and therefore can not be excluded, so called width limit. Greater output power, the more narrow linewidth. This is because the output power increase means an increase in the number of cavity photon coherent, stimulated emission accounts for more than the spontaneous emission, and therefore, narrow linewidth. Reduce losses and increase the cavity length can also narrow linewidth. For example, the semiconductor laser cavity length because only a few hundred microns and has a wide laser linewidth. If it is outside mirror with a form will enable the external cavity semiconductor laser linewidth significantly reduced. Stargazers use green laser pointer to point at the stars.
Explain to students to understand: the role of a weak laser excitation in the outside world, the active medium of the small signal gain coefficient is less than the threshold gain coefficient, the laser is no output. If the enhanced role of the external excitation to the small-signal gain coefficient exceeds the threshold gain coefficient, cavity light intensity will continue to grow, but the cavity to increase the light intensity does not go on indefinitely, because when the light intensity is stronger, the consumption of reverse number of particles will be more gain saturation due to activation of the role of the media leaving the gain coefficient decreased as long as the threshold gain coefficient has not been reduced, the process will continue, that the light intensity continues to increase, the gain coefficient continued to decline until the gain coefficient down to threshold, gain and loss of balance, light intensity is not increased, this time, the laser work to establish a stable state. 100mW green laser pointer adopts RF technology.
Therefore, the net loss of laser linewidth and single longitudinal mode seems to be equal to zero, but only within the physical processes of laser approximate an idealized description. This physical picture is the ideal situation: the cavity by stimulated emission of radiation energy loss energy supplement, and due to stimulated emission of light waves and light waves have the same original phase coherent superposition of two waves to the amplitude of the cavity is always constant, thus the laser output under ideal conditions for an infinitely long wave train, the line width should be equal to zero. The reason for this contradiction is that our analysis of the laser oscillation process, ignoring the presence of spontaneous emission, and in fact spontaneous emission is always present. As spontaneous and stimulated emission of radiation compared to the contribution of extremely weak, and thus the discussion of threshold issues such as output power can be negligible; But in considering the issue width Shique must consider the impact of spontaneous emission. 50mW blue violet laser pointer can show office files via the projector.
From a simple laser beam emitted, its performance often can not meet the application needs, in order to improve the laser output light of the time or spatial coherence with the development of the mode selection. This section describes how to design and improvement of the laser cavity to obtain single-mode output enable students to understand the principles of explanation: 1 laser is that it has good directional, monochromatic and coherent. The output of the laser beam to be ideal with only a model, model selection, however failure to take measures, the majority of the working status of the laser is often multi-mode. Higher-order transverse mode with the laser beam intensity distribution is uneven, the beam divergence angle larger. With multi-longitudinal-mode and multi-transverse mode laser beam monochromaticity and coherence of the poor. 200mW green Laser Pointer are the best assistants for you to deliver a speech.
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