Interference of two identical laser source Do two identical but separate laser sources cancel out each other when point on the same spot? By the way both light will be coming from same direction. And of course, they will have a phase difference of PI. Is there a video or documentation of such an experiment (or a similar one)?
 A: For two perfect laser sources without noise (infinite narrow linewidth) and of same amplitude, you could achieve this when both sources have the same frequency and same polarization. You need to control the length of one pathway to control the relative phase to $\phi_0=\pi$:
$E=E_1+E_2=E_0 (sin(\omega t)+sin(\omega t+\phi_0))$
The problem in general will be that your source is subject to phase noise (neglecting amplitude noise at this place):
$E_1=E_0 sin(\omega t+\varphi_1(t))$
When you use independent lasers, these noise processes $\varphi_1(t)$ and $\varphi_2(t)$ are uncorrelated and won't cancel out:
$E=2 E_0 \cdot sin(\omega t)\cdot cos(\varphi_1(t)-\varphi_2(t)-\phi_0)$
If the two lasers had very little noise, this could work for some time. To synchronize the lasers, you would try to relate both laser noises (phase-locking).
A: The simple answer is no, but that's because two separate laser beams cannot directly "com(ing) from same direction". Any two beams from separate sources which shine on a target with the centers aligned will have slightly different angles, and the distances from the emitter (and therefor the relative phase) will vary with location on the target. It's true that you can combine two beams with a beamsplitter, and theoretically get perfectly merged beams. In fact, this is the idea behind the Michelson interferometer, which splits a single beam into two, then recombines them. The reason you normally see a fringe pattern on such an interferometer is one of practicality. As the Wiki article states, 

If there is perfect spatial alignment between the returning beams,
  then there will not be any such pattern but rather a constant
  intensity over the beam dependent on the differential pathlength; this
  is difficult, requiring very precise control of the beam paths.

Since the alignment is so critical, it's just not worth taking the trouble for most setups. Also, with a standard fringe display you can see the effect of motion of the variable path length by observing the direction of motion of the fringes; a perfectly aligned system loses this information.
With that said, it is actually pretty easy to get effectively perfect alignment of an interferometer: use a retroreflector instead of a plane mirror for the moving target. Alignment accuracy of a few seconds of arc are fairly common, which is much better than is convenient with flat mirrors. Such retroreflectors are the heart of most laser distance measurement systems, but the apparent loss of motion direction information requires added complexity in the system to recover it. See this paper for a good overview.
A: It depends, if the frequency is identical and the waves are in the same phase, they do not cancel out. Only when the phase is exactly 1/2 out of phase, they will completely cancel out.(if you point them from the exact same location)
!http://cns-alumni.bu.edu/~slehar/PhaseConjugate/PhaseConjugate_files/image009.jpg
You can take a look here. This aren't two lasers, but i hope you understand what will happen if we change it too two lasers.
http://www.physicsclassroom.com/class/light/Lesson-1/Two-Point-Source-Interference
