3
$\begingroup$

Wikipedia states that Spatial coherence in lasers allows them to be focused to a tight spot and also allows a laser beam to stay narrow over great distances. About temporal coherent laser it states that temporal coherence allows them to emit light with a very narrow spectrum. I know what temporal and spatial coherence is but i don't understand how the laser formed by them have different properties. What is underlying physics of characteristics shown by above mentioned two laser types?

$\endgroup$
  • $\begingroup$ Your question - not clear. Are you asking what mechanisms are required in laser design to achieve spatial and temporal coherence? $\endgroup$ – docscience Dec 20 '16 at 19:39
3
$\begingroup$

Your question is not very clear at the moment, so let me give some practical ideas.

  • Spatial coherence means that all portions of the laser beam have all the same phase. When you want to focus this laser (for instance with a lens), the light close to the focus is a combination of all the portions of the initial beam, added constructively. If one portion is out of phase, it may contribute destructively. On the other hand, the light far from the focus is also a combination, but the contributions of different portions add destructively. If one portion is out of phase, it may contribute constructively. In consequence, when a portion is out of phase, it will not contribute in the focus, but it may contribute ouside => it destroys the quality of the focusing.

  • Temporal coherence means the laser stays in phase compared to the phase it had some time ago. If the phase slowly shifts, it means that the oscillations of the wave have become slightly longer or shorter at some point. In other words, the light wavelength also shifts slowly. This means that the spectrum of the laser is not composed of only one wavelength, but of a bunch of slightly different wavelengths.

| cite | improve this answer | |
$\endgroup$
0
$\begingroup$

temporal coherence is a measure of the correlation of the phase of the light wave at different points along the direction of propagation .It tells us how monochromatic a source is

Spatial coherence is the beam of light specifically a laser to a tight spot and also allow a laser beam to stay narrow over a large distance.

| cite | improve this answer | |
$\endgroup$

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.