# Laser ray composition

Hello,
I am kindly asking for some help with following theoretical problem.

Imagine at least two lasers emitting light at certain wavelength, each from different angle. Imagine that the rays cross at some point.

Is is possible to observe at the crossing point light of different wavelength than the wavelength of each laser? In other words, is it possible to achieve light of higher energy while combining two lower energy lasers at the point of their contact?

Thank you for clarification and/or sources.

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blue_leaf77
Homework Helper
Is is possible to observe at the crossing point light of different wavelength than the wavelength of each laser?
No, it's not possible. You are not creating new photons with different energy by combining two laser beams, instead they will only produce interference pattern (provided the two lasers have a good correlation between them, which is not likely the case when the interfering beams come from separate lasers).
In other words, is it possible to achieve light of higher energy while combining two lower energy lasers at the point of their contact?
Not either, the reason of which is explained above.

tech99
Gold Member
No, it's not possible. You are not creating new photons with different energy by combining two laser beams, instead they will only produce interference pattern (provided the two lasers have a good correlation between them, which is not likely the case when the interfering beams come from separate lasers).

Not either, the reason of which is explained above.
I would have expected the common volume to have "power in" equal to "power out". But in a general case I would also expect to find a moving beat pattern in the common volume. Where crests of the two waves meet, I would expect the E-field to be doubled and the power flux density to be quadrupled.

blue_leaf77
Homework Helper
The beat pattern is nothing but an interference pattern between the two beams.
I would expect the E-field to be doubled and the power flux density to be quadrupled.
That's true, which is a result from interference. Anyway, no new photons with different energy from those of the laser are generated, as asked by the OP.

Redbelly98
Staff Emeritus
Homework Helper
Where crests of the two waves meet, I would expect the E-field to be doubled and the power flux density to be quadrupled.
If the two laser beams have the same energy, yes -- and where the two waves destructively interfere, the power flux density would be zero. So on average, it is doubled in the region of overlap, as is the total overall power. No surprise there -- the total power is simply the sum of the powers in the two beams, or twice the power in one beam. Energy Conservation holds.

Andy Resnick
Hello,
I am kindly asking for some help with following theoretical problem.

Imagine at least two lasers emitting light at certain wavelength, each from different angle. Imagine that the rays cross at some point.

Is is possible to observe at the crossing point light of different wavelength than the wavelength of each laser? In other words, is it possible to achieve light of higher energy while combining two lower energy lasers at the point of their contact?

Thank you for clarification and/or sources.
Only for very high laser powers- when the matter-light interaction becomes nonlinear. Then you can observe sum and difference frequency generation (and many other effects). This lasers also need to be mutually coherent, IIRC. See, for example, Boyd's 'Nonlinear Optics".

sophiecentaur