# Atomic Physics: Optical molasses

• Niles
In summary, the conversation is about the force used in Optical Molasses, which is given by a formula involving the saturation parameter and the atom's excited state lifetime. The force saturates to half of its maximum value, which is explained by the fact that an atom can only absorb and emit a photon twice during its excited state lifetime. However, the question arises as to where the factor of 1/2 comes from in this interpretation of the force.
Niles

## Homework Statement

Hi

I have a question regarding the force that it used in Optical Molasses. The force is generally given by
$$F = \frac{\hbar k}{2} \frac{s_0}{1 + s_0+ (2\delta/\Gamma)^2}$$
where s0 is the saturation parameter. The force saturates to
$$F = \frac{\hbar k}{2}$$
It is normally said that this result is a consequence of the fact that the atom can only absorb and subsequently emit a photon twice during its excited state lifetime. However this latter statement does not make sense to me intuitively. I would say that once the atom has absorbed a photon, then -- on average -- it takes a time $1/\Gamma$ to emit it. So the remaining factor 1/2, where does this come in when looking at the problem like this?Niles.

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Just to clarify, my question is the following: The intuitive picture often presented is that when an atom absorbs a photon, on average a time $\tau=1/\Gamma$ passes by until the atom emits the photon again. So the force is (under the condition that the atom is in resonance with the light so that the probability of absorbing a photon is maximal)
$$F = \frac{\Delta p}{\Delta t} = \frac{\hbar k }{\tau} = \hbar k \Gamma$$
But we know that the maximum force is given by (see my OP)
$$F = \hbar k \frac{\Gamma }{2}$$
So my question is, where does the factor of 1/2 come from, when this framework is used to interpret the force?Niles.

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## 1. What is atomic physics?

Atomic physics is the branch of physics that studies the behavior and properties of atoms, including their structure, interactions, and energy levels.

## 2. What is optical molasses?

Optical molasses is a technique used in atomic physics to cool and trap atoms using lasers. By shining multiple laser beams at the atoms, they are slowed down and confined in a small space, allowing for more precise measurements and control of their behavior.

## 3. How does optical molasses work?

Optical molasses works by using laser beams to create a standing wave of light, which exerts a force on the atoms. This force counteracts the random thermal motion of the atoms, causing them to slow down and be confined in the center of the standing wave.

## 4. What are the applications of optical molasses?

Optical molasses has a wide range of applications in atomic physics, including atomic clocks, quantum computing, and precision measurements of atomic properties. It is also used in the production of Bose-Einstein condensates, a state of matter with unique quantum properties.

## 5. Are there any limitations to optical molasses?

While optical molasses is a powerful tool in atomic physics, it does have some limitations. It is most effective for cooling and trapping atoms with low mass and high scattering cross-sections, such as alkali metals. Additionally, it is limited by the type and power of lasers available for use.

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