Laser detuning

[1] This technique is essential in many AMO physics experiments and associated technologies, as it allows the manipulation of light-matter interactions with high precision.

Detuning has use cases in research fields including quantum optics, laser cooling, and spectroscopy.

By adjusting the detuning, researchers and engineers can control absorption, emission, and scattering processes, making it a versatile tool in both fundamental and applied physics.

The laser detuning is important for a resonant system such as a cavity because it determines the phase (modulo 2

The probability of a stimulated emission or absorption event depends on the strength of the detuning and is represented by a Lorentzian profile:

Engineering the laser detuning in this way to a specific red shifted value is the basis for Doppler cooling.

For high-intensity lasers, power broadening occurs, altering the effective linewidth.

quantifies the strength of the atom-laser coupling and is related to detuning by the generalized Rabi formula:

One of the earliest examples of high-impact work demonstrating the practical uses of laser detuning was Arthur Ashkin’s research in the 1970s, resulting in the first optical trapping demonstrations for which he was awarded the 2018 Nobel Prize in Physics.

[3] Another fundamental advancement in laser physics utilizing detuning was Steven Chu's development of Doppler cooling in the 1980s, demonstrating the role of red-detuned lasers in reducing atomic velocities, for which he was awarded the 1997 Nobel Prize in Physics.

Rubidium, caesium, and other alkali atoms are common examples, with cooling light tuned near their

When extended to three-dimensions, the Doppler cooling technique is often referred to as optical molasses.

In such an arrangement, three orthogonal pairs of red-detuned lasers create a viscous “molasses” that slows the motion of the trapped atoms in all three spatial dimensions.

The magnetic field induces a spatially varying Zeeman shift, that when coupled with proper molasses beam red-detuning, preferentially pushes the atoms towards the center of the trap.

In high-resolution spectroscopy, detuning enhances the ability to distinguish closely spaced energy levels.

One specific use case is two-photon spectroscopy, which is when a laser is detuned away from intermediate states to allow access to higher-energy states without populating the lower levels, reducing background noise.

Another example is isotope-selective spectroscopy, which is when laser detuning is adjusted to enable selective excitation of isotopes with slightly shifted transition frequencies.

Similar to the laser cooling of atoms, the sign of the detuning plays an important part in optomechanical applications.

[5][6] In the red detuned regime, the optomechanical system undergoes cooling and coherent energy transfer between the light and the mechanical mode (a "beam splitter").

In the blue-detuned regime, it undergoes heating, mechanical amplification and possibly squeezing and entanglement.

The on-resonance case when the laser detuning is zero, can be used for very sensitive detection of mechanical motion, such as used in LIGO.

[7] PDH locking utilizes phase-modulated sidebands detuned red and blue detuned from the carrier frequency to stabilize the laser frequency relative to a stable optical reference such as a high-finesse optical cavity, resonator, or atomic spectroscopy.

The cavity transmission is sent to a high-speed photodetector and when the laser frequency is resonant with the system, the power is minimized.

Atomic clocks utilize laser detuning to probe specific and spectrally narrow hyperfine transitions in rubidium, caesium, strontium, and other elements.

[8] Optical tweezers[3] utilize red and blue laser detuning to trap particles for analysis from the sub-nanometer to micron scale, enabling advancements in many fields including biology and medicine.

Laser detuning does not have to be static and can be dynamically varied in advanced techniques to achieve specific effects.

This is used in stimulated Raman adiabatic passage to enable smooth transitions between quantum states, which can be used for qubit control.