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Advanced Physics
1. Consider a laser beam initially having a flat phase front. After the propagation time of To, the maximum phase offset is 1/3, what is
the coherent time of this laser beam? What is the corresponding coherent length? Additional info: in practice, what matters the
most is the statistical property of the laser beam and thus the maximum phase offset is not as important as the standard deviation.
2. Describe the Electric Dipole Approximation. When can we use it? Why do we need to use it?
3. Consider a molecular beam moving with a constant velocity v away from the observer and making an angle between the velocity v
and the vector connecting the observer and the molecule. What is the observed resonant frequency, considering the actual
resonance frequency of o?
4. Show that population inversion is impossible in a two-level system. Show that population inversion is possible in a three-level
system. Show that four-level system is the easiest to achieve population inversion.
5. What is the similarity between a fiber laser and a semiconductor laser? Please explain why the flash lamps are more likely suitable
for pumping solid-state media and not gas media. What is more suitable for gas media as a pumping source?​

Answer 1

Answer:

Time remaining: 00:06:54 Advanced Physics 1. Consider a laser beam initially having a flat phase front. After the ... What is the corresponding coherent length?

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