Laser Detuning on:
[Wikipedia]
[Google]
[Amazon]
In
Similar to the laser cooling of atoms, the sign of the detuning plays an important part in Optomechanical applications. 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
optical physics
Atomic, molecular, and optical physics (AMO) is the study of matter-matter and light-matter interactions; at the scale of one or a few atoms and energy scales around several electron volts. The three areas are closely interrelated. AMO theory in ...
, laser detuning is the tuning of a laser
A laser is a device that emits light through a process of optical amplification based on the stimulated emission of electromagnetic radiation. The word "laser" is an acronym for "light amplification by stimulated emission of radiation". The fi ...
to a frequency
Frequency is the number of occurrences of a repeating event per unit of time. It is also occasionally referred to as ''temporal frequency'' for clarity, and is distinct from ''angular frequency''. Frequency is measured in hertz (Hz) which is eq ...
that is slightly off from a quantum system
Quantum mechanics is a fundamental theory in physics that provides a description of the physical properties of nature at the scale of atoms and subatomic particles. It is the foundation of all quantum physics including quantum chemistry, ...
's resonant frequency. When used as a noun, the laser detuning is the difference between the resonance frequency
Frequency is the number of occurrences of a repeating event per unit of time. It is also occasionally referred to as ''temporal frequency'' for clarity, and is distinct from ''angular frequency''. Frequency is measured in hertz (Hz) which is eq ...
of the system and the laser's optical frequency (or wavelength
In physics, the wavelength is the spatial period of a periodic wave—the distance over which the wave's shape repeats.
It is the distance between consecutive corresponding points of the same phase on the wave, such as two adjacent crests, t ...
). Lasers tuned to a frequency below the resonant frequency are called ''red-detuned'', and lasers tuned above resonance are called ''blue-detuned''.
Illustration
Consider a system with a resonance frequency in the optical frequency range of theelectromagnetic spectrum
The electromagnetic spectrum is the range of frequencies (the spectrum) of electromagnetic radiation and their respective wavelengths and photon energies.
The electromagnetic spectrum covers electromagnetic waves with frequencies ranging fro ...
, i.e. with frequency of a few THz to a few PHz, or equivalently with a wavelength in the range of 10 nm to 100 μm. If this system is excited by a laser with a frequency close to this value, the laser detuning is then defined as:The most common examples of such resonant systems in the optical frequency range are optical cavities (free-space, fiber or microcavities), atoms, and dielectrics or semiconductors.
The laser detuning is important for a resonant system such as a cavity because it determines the phase (modulo 2π) acquired by the laser field per roundtrip. This is important for linear optical processes such as interference and scattering, and extremely important for nonlinear optical
Nonlinear optics (NLO) is the branch of optics that describes the behaviour of light in ''nonlinear media'', that is, media in which the polarization density P responds non-linearly to the electric field E of the light. The non-linearity is typic ...
processes because it affects the phase-matching
Nonlinear optics (NLO) is the branch of optics that describes the behaviour of light in ''nonlinear media'', that is, media in which the polarization density P responds non-linearly to the electric field E of the light. The non-linearity is typica ...
condition.
Applications
Laser cooling of atoms
Lasers can be detuned in thelab frame
In theoretical physics, a local reference frame (local frame) refers to a coordinate system or frame of reference that is only expected to function over a small region or a restricted region of space or spacetime.
The term is most often used in t ...
so that they are Doppler shifted to the resonant frequency in a moving system, which allows lasers to affect only atoms moving at a specific speed or in a specific direction and makes laser detuning a central tool of laser cooling
Laser cooling includes a number of techniques in which atoms, molecules, and small mechanical systems are cooled, often approaching temperatures near absolute zero. Laser cooling techniques rely on the fact that when an object (usually an atom) a ...
and magneto-optical trap
A magneto-optical trap (MOT) is an apparatus which uses laser cooling and a spatially-varying magnetic field to create a trap which can produce samples of cold, trapped, neutral atoms. Temperatures achieved in a MOT can be as low as several micro ...
s.
Optomechanics
Similar to the laser cooling of atoms, the sign of the detuning plays an important part in Optomechanical applications. 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
The Laser Interferometer Gravitational-Wave Observatory (LIGO) is a large-scale physics experiment and observatory designed to detect cosmic gravitational waves and to develop gravitational-wave observations as an astronomical tool. Two large ...
.
References