# How to convert m meter into recoils

1. Aug 19, 2008

### texophist

Hi
as the single photon recoil is p=hbar k
and k=2pi/lambda

2. Aug 19, 2008

### Redbelly98

Staff Emeritus
What is it you want to know? The velocity change of an atom that absorbs or emits a photon?

Single-photon recoil can be expressed as a momentum or as a velocity. It doesn't make sense to express it as a distance (as your implying by asking about meters). Can you explain some more about what you wish to know?

3. Aug 19, 2008

### texophist

yes yu are right,
I just wanna calculate the width of a velocity distribution in recoils.
if e.g 1 pixel=2 micro meter, which is the width in pixel or microns,
how ca we express this width in recoils.
thanx

4. Aug 20, 2008

### Redbelly98

Staff Emeritus
Here is a "3-step program":

1. Divide the recoil momentum by the atom's (or molecule's) mass. This gives you the recoil velocity:
vrec = hbar k / M

2. Express the width of the velocity distribution in velocity units, such as m/s. (Not in pixels or micro meters, that is not making sense to me.)

3. With the recoil velocity and velocity width expressed in the same velocity units, take their ratio:

[width in recoils] = vwidth / vrec

5. Aug 20, 2008

Thanx alot