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<title>Laser cooling</title>

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<span id="openzim-page-title" class="mw-page-title-main"><span class="mw-page-title-main">Laser cooling</span></span>

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<p><b>Laser cooling</b> includes several techniques where <a href="Atom" title="Atom">atoms</a>, <a href="Molecule" title="Molecule">molecules</a>, and small mechanical systems are cooled with <a href="Laser" title="Laser">laser</a> light. The directed energy of lasers is often associated with heating materials, e.g. <a href="Laser_cutting" title="Laser cutting">laser cutting</a>, so it can be counterintuitive that laser cooling often results in sample <a href="Temperature" title="Temperature">temperatures</a> approaching <a href="Absolute_zero" title="Absolute zero">absolute zero</a>. It is a routinely used in atomic physics experiments where the laser-cooled atoms are manipulated and measured, or in technologies, such as atom-based quantum computing architectures.

</p><p>Laser cooling reduces the random motion of particles or the random vibrations of mechanical systems. For atoms and molecules this reduces Doppler shifts in spectroscopy, allowing for high precision measurements and instruments such as <a href="Optical_clock" title="Optical clock">optical clocks</a>. The reduction in thermal energy also allows for efficient loading of atoms and molecules into traps where they can be used in experiments or atom-based devices for longer periods of time.

</p><p>Laser cooling relies on the momentum change when an object, such as an atom, absorbs and re-emits a <a href="Photon" title="Photon">photon</a> (a particle of light). Atoms will be cooled in one dimension if they are illuminated by a pair of counter-propagating laser beams that are detuned below an atomic transition. The laser light will be preferentially absorbed from the laser beam that counter-propagates with respect to the atom's motion due to the <a href="Doppler_effect" title="Doppler effect">Doppler effect</a>. The absorbed light is re-emitted by the atom in a random direction. After this process is repeated the random motion of the atoms will be reduced along the laser cooling axis. With three pairs of counter-propagating laser beams along all three axes a warm cloud of atoms will be cooled in three dimensions. The atom cloud will expand more slowly because of the decrease in the cloud's velocity distribution, which corresponds to a lower temperature and therefore colder atoms. For an ensemble of particles, their <a href="Thermodynamic_temperature" title="Thermodynamic temperature">thermodynamic temperature</a> is proportional to the <a href="Variance" title="Variance">variance</a> in their velocity, therefore the lower the distribution of velocities, the lower the temperature of the particles.

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<div class="mw-heading mw-heading2"><h2 id="History">History</h2></div>

<div class="mw-heading mw-heading3"><h3 id="Radiation_pressure">Radiation pressure</h3></div>

<p><a href="Radiation_pressure" title="Radiation pressure">Radiation pressure</a> is the force that electromagnetic radiation exerts on matter. In 1873 Maxwell published his treatise on <a href="Electromagnetism" title="Electromagnetism">electromagnetism</a> in which he predicted radiation pressure.<sup id="cite_ref-Maxwell1873_1-0" class="reference"><a href="#cite_note-Maxwell1873-1"><span class="cite-bracket">[</span>1<span class="cite-bracket">]</span></a></sup> The force was experimentally demonstrated for the first time by <a href="Pyotr_Lebedev" title="Pyotr Lebedev">Lebedev</a> and reported at a conference in Paris in 1900,<sup id="cite_ref-Lebedev1900_2-0" class="reference"><a href="#cite_note-Lebedev1900-2"><span class="cite-bracket">[</span>2<span class="cite-bracket">]</span></a></sup> and later published in more detail in 1901.<sup id="cite_ref-Lebedew1901_3-0" class="reference"><a href="#cite_note-Lebedew1901-3"><span class="cite-bracket">[</span>3<span class="cite-bracket">]</span></a></sup> Following Lebedev's measurements <a href="Ernest_Fox_Nichols" title="Ernest Fox Nichols">Nichols</a> and <a href="Gordon_Ferrie_Hull" title="Gordon Ferrie Hull">Hull</a> also demonstrated the force of radiation pressure in 1901,<sup id="cite_ref-Nichols1901_4-0" class="reference"><a href="#cite_note-Nichols1901-4"><span class="cite-bracket">[</span>4<span class="cite-bracket">]</span></a></sup> with a refined measurement reported in 1903.<sup id="cite_ref-Nichols1_5-0" class="reference"><a href="#cite_note-Nichols1-5"><span class="cite-bracket">[</span>5<span class="cite-bracket">]</span></a></sup><sup id="cite_ref-Nichols2_6-0" class="reference"><a href="#cite_note-Nichols2-6"><span class="cite-bracket">[</span>6<span class="cite-bracket">]</span></a></sup>

</p><p>Atoms and molecules have bound states and transitions can occur between these states in the presence of light that is near the transition frequency. Sodium is historically notable because it has a strong transition at 589 nm, a wavelength which is close to the peak sensitivity of the human eye. This made it relatively easy to see the interaction of light with sodium atoms. In 1933, <a href="Otto_Frisch" class="mw-redirect" title="Otto Frisch">Otto Frisch</a> deflected an atomic beam of sodium atoms with light.<sup id="cite_ref-Frisch_7-0" class="reference"><a href="#cite_note-Frisch-7"><span class="cite-bracket">[</span>7<span class="cite-bracket">]</span></a></sup>

This was the first realization of radiation pressure acting on an atom or molecule.

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<div class="mw-heading mw-heading3"><h3 id="Laser_cooling_proposals">Laser cooling proposals</h3></div>

<p>The introduction of <a href="Laser" title="Laser">lasers</a> in atomic physics experiments was the precursor to the laser cooling proposals in the mid 1970s. Laser cooling was proposed separately in 1975 by two different research groups: <a href="Theodor_W._H%C3%A4nsch" title="Theodor W. Hänsch">Hänsch</a> and <a href="Arthur_Leonard_Schawlow" title="Arthur Leonard Schawlow">Schawlow</a>,<sup id="cite_ref-Hänsch1975_8-0" class="reference"><a href="#cite_note-Hänsch1975-8"><span class="cite-bracket">[</span>8<span class="cite-bracket">]</span></a></sup> and <a href="David_Wineland" class="mw-redirect" title="David Wineland">Wineland</a> and <a href="Hans_Georg_Dehmelt" title="Hans Georg Dehmelt">Dehmelt</a>.<sup id="cite_ref-9" class="reference"><a href="#cite_note-9"><span class="cite-bracket">[</span>9<span class="cite-bracket">]</span></a></sup> Both proposals outlined the simplest laser cooling process, known as <a href="Doppler_cooling" title="Doppler cooling">Doppler cooling</a>, where laser light tuned below an atom's resonant frequency is preferentially absorbed by atoms moving towards the laser and after absorption a photon is emitted in a random direction. This process is repeated many times and in a configuration with counterpropagating laser cooling light the velocity distribution of the atoms is reduced.<sup id="cite_ref-:0_10-0" class="reference"><a href="#cite_note-:0-10"><span class="cite-bracket">[</span>10<span class="cite-bracket">]</span></a></sup>

</p><p>In 1977 <a href="Arthur_Ashkin" title="Arthur Ashkin">Ashkin</a> submitted a paper which describes how Doppler cooling could be used to provide the necessary damping to load atoms into an optical trap.<sup id="cite_ref-11" class="reference"><a href="#cite_note-11"><span class="cite-bracket">[</span>11<span class="cite-bracket">]</span></a></sup> In this work he emphasized how this could allow for long <a href="Spectroscopy" title="Spectroscopy">spectroscopic</a> measurements which would increase precision because the atoms would be held in place. He also discussed overlapping <a href="Optical_tweezers" title="Optical tweezers">optical traps</a> to study interactions between different atoms.

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<div class="mw-heading mw-heading3"><h3 id="Initial_realizations">Initial realizations</h3></div>

<p>Following the laser cooling proposals, in 1978 two research groups that Wineland, Drullinger and Walls of NIST, and Neuhauser, Hohenstatt, Toscheck and Dehmelt of the University of Washington succeeded in laser cooling atoms. The NIST group wanted to reduce the effect of Doppler broadening on spectroscopy. They cooled magnesium ions in a Penning trap to below 40 K. The Washington group cooled barium ions.

</p><p>Influenced by the Wineland's work on laser cooling ions, <a href="William_Daniel_Phillips" title="William Daniel Phillips">William Phillips</a> applied the same principles to laser cool neutral atoms. In 1982, he published the first paper where neutral atoms were laser cooled.<sup id="cite_ref-12" class="reference"><a href="#cite_note-12"><span class="cite-bracket">[</span>12<span class="cite-bracket">]</span></a></sup> The process used is now known as the <a href="Zeeman_slower" title="Zeeman slower">Zeeman slower</a> and is a standard technique for slowing an atomic beam.

</p><p>The 1997 <a href="Nobel_Prize_in_Physics" title="Nobel Prize in Physics">Nobel Prize in Physics</a> was awarded to <a href="Claude_Cohen-Tannoudji" title="Claude Cohen-Tannoudji">Claude Cohen-Tannoudji</a>, <a href="Steven_Chu" title="Steven Chu">Steven Chu</a>, and <a href="William_Daniel_Phillips" title="William Daniel Phillips">William Daniel Phillips</a> "for development of methods to cool and trap atoms with laser light".<sup id="cite_ref-13" class="reference"><a href="#cite_note-13"><span class="cite-bracket">[</span>13<span class="cite-bracket">]</span></a></sup>

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<div class="mw-heading mw-heading3"><h3 id="Modern_advances">Modern advances</h3></div>

<div class="mw-heading mw-heading4"><h4 id="Atoms">Atoms</h4></div>

<p>The Doppler cooling limit for electric dipole transitions is typically in the hundreds of microkelvins. In the 1980s this limit was seen as the lowest achievable temperature. It was a surprise then when sodium atoms were cooled to 43 microkelvins when their Doppler cooling limit is 240 microkelvins,<sup id="cite_ref-14" class="reference"><a href="#cite_note-14"><span class="cite-bracket">[</span>14<span class="cite-bracket">]</span></a></sup> this unforeseen low temperature was explained by considering the interaction of polarized laser light with more atomic states and transitions. Previous conceptions of laser cooling were decided to have been too simplistic.<sup id="cite_ref-:1_15-0" class="reference"><a href="#cite_note-:1-15"><span class="cite-bracket">[</span>15<span class="cite-bracket">]</span></a></sup> The major laser cooling breakthroughs in the 70s and 80s led to several improvements to preexisting technology and new discoveries with temperatures just above <a href="Absolute_zero" title="Absolute zero">absolute zero</a>. The cooling processes were utilized to make <a href="Atomic_clock" title="Atomic clock">atomic clocks</a> more accurate and to improve spectroscopic measurements, and led to the observation of a new <a href="State_of_matter" title="State of matter">state of matter</a> at ultracold temperatures.<sup id="cite_ref-:2_16-0" class="reference"><a href="#cite_note-:2-16"><span class="cite-bracket">[</span>16<span class="cite-bracket">]</span></a></sup><sup id="cite_ref-:1_15-1" class="reference"><a href="#cite_note-:1-15"><span class="cite-bracket">[</span>15<span class="cite-bracket">]</span></a></sup> The new state of matter, the <a href="Bose%E2%80%93Einstein_condensate" title="Bose–Einstein condensate">Bose–Einstein condensate</a>, was observed in 1995 by <a href="Eric_Allin_Cornell" title="Eric Allin Cornell">Eric Cornell</a>, <a href="Carl_Wieman" title="Carl Wieman">Carl Wieman</a>, and <a href="Wolfgang_Ketterle" title="Wolfgang Ketterle">Wolfgang Ketterle</a>.<sup id="cite_ref-17" class="reference"><a href="#cite_note-17"><span class="cite-bracket">[</span>17<span class="cite-bracket">]</span></a></sup>

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<div class="mw-heading mw-heading4"><h4 id="Exotic_Atoms">Exotic Atoms</h4></div>

<p>Most laser cooling experiments bring the atoms close to at rest in the laboratory frame, but cooling of relativistic atoms has also been achieved, where the effect of cooling manifests as a narrowing of the velocity distribution. In 1990, a group at <a href="Johannes_Gutenberg-Universit%C3%A4t_Mainz" class="mw-redirect" title="Johannes Gutenberg-Universität Mainz">JGU</a> successfully laser-cooled a beam of <sup>7</sup>Li<sup>+</sup> at <span class="nowrap">13.3 MeV</span> in a storage ring <sup id="cite_ref-18" class="reference"><a href="#cite_note-18"><span class="cite-bracket">[</span>18<span class="cite-bracket">]</span></a></sup> from <span class="nowrap">260 K</span> to lower than <span class="nowrap">2.9 K</span>, using two counter-propagating lasers addressing the same transition, but at <span class="nowrap">514.5 nm</span> and <span class="nowrap">584.8 nm</span>, respectively, to compensate for the large <a href="Doppler_effect" title="Doppler effect">Doppler shift</a>.

</p><p>Laser cooling of antimatter has also been demonstrated, first in 2021 by the <a href="ALPHA_experiment" title="ALPHA experiment">ALPHA</a> collaboration on antihydrogen atoms.<sup id="cite_ref-19" class="reference"><a href="#cite_note-19"><span class="cite-bracket">[</span>19<span class="cite-bracket">]</span></a></sup> In 2024, <a href="Positronium" title="Positronium">positronium</a>, made up of an electron and a positron, was laser cooled to about 1K.<sup id="cite_ref-20" class="reference"><a href="#cite_note-20"><span class="cite-bracket">[</span>20<span class="cite-bracket">]</span></a></sup>

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<div class="mw-heading mw-heading4"><h4 id="Molecules">Molecules</h4></div>

<p>Molecules are significantly more challenging to laser cool than atoms because molecules have vibrational and rotational degrees of freedom. These extra degrees of freedom result in more energy levels that can be populated from excited state decays, requiring more lasers compared to atoms to address the more complex level structure. Vibrational decays are particularly challenging because there are no symmetry rules that restrict the vibrational states that can be populated.

</p><p>In 2010, at team at Yale led by <a href="David_DeMille" title="David DeMille">Dave DeMille</a> successfully laser-cooled a <a href="Diatomic_molecule" title="Diatomic molecule">diatomic molecule</a>.<sup id="cite_ref-21" class="reference"><a href="#cite_note-21"><span class="cite-bracket">[</span>21<span class="cite-bracket">]</span></a></sup> In 2016, a group at <a href="Max-Planck-Institut_f%C3%BCr_Quantenoptik" class="mw-redirect" title="Max-Planck-Institut für Quantenoptik">MPQ</a> successfully cooled <a href="Formaldehyde" title="Formaldehyde">formaldehyde</a> to <span class="nowrap">420 μK</span> via optoelectric Sisyphus cooling.<sup id="cite_ref-22" class="reference"><a href="#cite_note-22"><span class="cite-bracket">[</span>22<span class="cite-bracket">]</span></a></sup> In 2022, a group at Harvard successfully laser cooled and trapped CaOH to <span class="nowrap">720(40) μK</span> in a <a href="Magneto-optical_trap" title="Magneto-optical trap">magneto-optical trap</a>.<sup id="cite_ref-23" class="reference"><a href="#cite_note-23"><span class="cite-bracket">[</span>23<span class="cite-bracket">]</span></a></sup>

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<div class="mw-heading mw-heading4"><h4 id="Mechanical_systems">Mechanical systems</h4></div>

<p>Starting in the 2000s, laser cooling was applied to <a href="Cavity_optomechanics" title="Cavity optomechanics">small mechanical systems</a>, ranging from small cantilevers to the mirrors used in the <a href="LIGO" title="LIGO">LIGO</a> observatory. These devices are connected to a larger substrate, such as a mechanical membrane attached to a frame, or they are held in optical traps, in both cases the mechanical system is a harmonic oscillator. Laser cooling reduces the random vibrations of the mechanical oscillator, removing thermal phonons from the system.

</p><p>In 2007, an MIT team successfully laser-cooled a macro-scale (1 gram) object to 0.8 K.<sup id="cite_ref-24" class="reference"><a href="#cite_note-24"><span class="cite-bracket">[</span>24<span class="cite-bracket">]</span></a></sup> In 2011, a team from the California Institute of Technology and the University of Vienna became the first to laser-cool a (10 μm × 1 μm) mechanical object to its quantum ground state.<sup id="cite_ref-25" class="reference"><a href="#cite_note-25"><span class="cite-bracket">[</span>25<span class="cite-bracket">]</span></a></sup>

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<div class="mw-heading mw-heading2"><h2 id="Methods">Methods</h2></div>

<p>The first realization of laser cooling and the most ubiquitous method for cooling atoms and molecules (so much so that it is often referred to simply as 'laser cooling'), is <a href="Doppler_cooling" title="Doppler cooling">Doppler cooling</a>.

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<div class="mw-heading mw-heading3"><h3 id="Doppler_cooling">Doppler cooling</h3></div>

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</style><div role="note" class="hatnote navigation-not-searchable">Main article: <a href="Doppler_cooling" title="Doppler cooling">Doppler cooling</a></div>

<p>Doppler cooling is by far the most common method of laser cooling. It is used to cool low density gases down to the <a href="Doppler_cooling_limit" class="mw-redirect" title="Doppler cooling limit">Doppler cooling limit</a>, which for <a href="Rubidium" title="Rubidium">rubidium</a> (a popular choice in the field of atomic physics) is around 150 <a href="https://en.wiktionary.org/wiki/microkelvin" class="extiw external" title="wiktionary:microkelvin">microkelvin</a>. It is often often combined with a magnetic field gradient to realize a <a href="Magneto-optical_trap" title="Magneto-optical trap">magneto-optical trap</a>.

</p><p>In Doppler cooling, initially, the frequency of light is tuned slightly below an <a href="Electronic_transition" class="mw-redirect" title="Electronic transition">electronic transition</a> in the <a href="Atom" title="Atom">atom</a>. Because the light is <a href="Laser_detuning" title="Laser detuning">detuned</a> to the "red" (i.e., at lower frequency) of the transition, the atoms will absorb more <a href="Photon" title="Photon">photons</a> if they move towards the light source, due to the <a href="Doppler_effect" title="Doppler effect">Doppler effect</a>. Thus if one applies light from two opposite directions, the atoms will always scatter more photons from the laser beam pointing opposite to their direction of motion. In each scattering event the atom loses a <a href="Momentum" title="Momentum">momentum</a> equal to the momentum of the photon. If the atom, which is now in the excited state, then emits a photon spontaneously, it will be kicked by the same amount of momentum, but in a random direction. Since the initial momentum change is a pure loss (opposing the direction of motion), while the subsequent change is random, the probable result of the absorption and emission process is to reduce the momentum of the atom, and therefore its <a href="Speed" title="Speed">speed</a>—provided its initial speed was larger than the recoil speed from scattering a single photon. If the absorption and emission are repeated many times, the average speed, and therefore the <a href="Kinetic_energy" title="Kinetic energy">kinetic energy</a> of the atom, will be reduced. Since the <a href="Temperature" title="Temperature">temperature</a> of a group of atoms is a measure of the average random internal kinetic energy, this is equivalent to cooling the atoms.

</p><p>When atoms are Doppler cooled in three dimensions, traditionally by 6 counter-propagating red-detuned laser beams, this is called <a href="Optical_molasses" title="Optical molasses">optical molasses</a> because the atoms move slowly, as if they are moving through molasses.

</p>

<div class="mw-heading mw-heading3"><h3 id="Sub-Doppler_cooling">Sub-Doppler cooling</h3></div>

<p>After Doppler cooling it is often helpful to cool atoms (or molecules) below their Doppler limit. This is accomplished with a variety sub-Doppler cooling techniques. Different atomic structures are amenable to different sub-Doppler cooling techniques. For example, <a href="Gray_molasses" title="Gray molasses">gray molasses</a> is used with lithium and potassium because they have unresolved hyperfine structure in their excited states where <a href="Polarization_gradient_cooling" title="Polarization gradient cooling">polarization gradient cooling</a> would not work.

</p><p>Sub-Doppler cooling methods include:

</p>

<ul><li><a href="Sisyphus_cooling" title="Sisyphus cooling">Sisyphus cooling</a><sup id="cite_ref-26" class="reference"><a href="#cite_note-26"><span class="cite-bracket">[</span>26<span class="cite-bracket">]</span></a></sup></li>

<li><a href="Polarization_gradient_cooling" title="Polarization gradient cooling">Polarization gradient cooling</a></li>

<li><a href="Resolved_sideband_cooling" title="Resolved sideband cooling">Resolved sideband cooling</a></li>

<li><a href="Raman_cooling" title="Raman cooling">Raman sideband cooling</a></li>

<li>Velocity selective coherent population trapping (VSCPT)<sup id="cite_ref-27" class="reference"><a href="#cite_note-27"><span class="cite-bracket">[</span>27<span class="cite-bracket">]</span></a></sup></li>

<li><a href="Gray_molasses" title="Gray molasses">Gray molasses</a></li>

<li><a href="Electromagnetically_induced_transparency" title="Electromagnetically induced transparency">Electromagnetically induced transparency (EIT)</a> cooling<sup id="cite_ref-28" class="reference"><a href="#cite_note-28"><span class="cite-bracket">[</span>28<span class="cite-bracket">]</span></a></sup></li></ul>

<div class="mw-heading mw-heading3"><h3 id="Other_methods">Other methods</h3></div>

<p>Other laser cooling methods include:

</p>

<ul><li>Cavity-mediated cooling<sup id="cite_ref-29" class="reference"><a href="#cite_note-29"><span class="cite-bracket">[</span>29<span class="cite-bracket">]</span></a></sup></li>

<li><a href="Anti-Stokes_cooling" title="Anti-Stokes cooling">Anti-Stokes cooling</a> in solids</li>

<li>Photonic cooling – It is under development as a spot cooling system that can target areas of hundreds of microns in diameter. The laser(s) cool a plate less than one millimeter thick, made largely of <a href="Gallium_arsenide" title="Gallium arsenide">gallium arsenide</a>.<sup id="cite_ref-:3_30-0" class="reference"><a href="#cite_note-:3-30"><span class="cite-bracket">[</span>30<span class="cite-bracket">]</span></a></sup></li></ul>

<div class="mw-heading mw-heading2"><h2 id="Applications">Applications</h2></div>

<p>Laser cooling is ubiquitous in the field of atomic physics. Reducing the random motion of atoms has several benefits, including the ability to trap atoms with optical or magnetic fields. Spectroscopic measurements of a cold atomic sample will also have reduced systematic uncertainties due to thermal motion.

</p><p>Often multiple laser cooling techniques are used in a single experiment to prepare a cold sample of atoms, which is then subsequently manipulated and measured. In a representative experiment a vapor of strontium atoms is generated in a hot oven that exit the oven as an atomic beam. After leaving the oven the atoms are Doppler cooled in two dimensions transverse to their motion to reduce loss of atoms due to divergence of the atomic beam. The atomic beam is then slowed and cooled with a Zeeman slower to optimize the atom loading efficiency into a magneto-optical trap (MOT), which Doppler cools the atoms, that operates on the <span class="nowrap"><sup>1</sup>S<sub>0</sub> → <sup>1</sup>P<sub>1</sub></span> with lasers at 461 nm. The MOT transitions from using light at 461 nm to using light at 689 nm to drive the <span class="nowrap"><sup>1</sup>S<sub>0</sub> → <sup>3</sup>P<sub>1</sub></span>, which is a narrow transition, to realize even colder atoms. The atoms are then transferred into an optical dipole trap where evaporative cooling gets them to temperatures where they can be effectively loaded into an optical lattice.

</p><p>Laser cooling is important for quantum computing efforts based on neutral atoms and trapped atomic ions. In an <a href="Ion_trap" title="Ion trap">ion trap</a> Doppler cooling reduces the random motion of the ions so they form a well-ordered crystal structure in the trap. After Doppler cooling the ions are often cooled to their motional ground state to reduce decoherence during quantum gates between ions.

</p><p>Photonic cooling is under development for use to cool chip hotspots in data centers.<sup id="cite_ref-:3_30-1" class="reference"><a href="#cite_note-:3-30"><span class="cite-bracket">[</span>30<span class="cite-bracket">]</span></a></sup>

</p>

<div class="mw-heading mw-heading2"><h2 id="Equipment">Equipment</h2></div>

<p>Laser cooling atoms requires scientific equipment that when assembled forms a cold atom machine. Such machines consist of two parts: a vacuum chamber which houses the laser cooled atoms and the laser systems used for cooling, as well as for preparing and manipulating atomic states and detecting the atoms. Laser cooling molecules generally requires more lasers and optical modulators (such as electro-optic and acousto-optic) to address the more complex molecular structure. Mechanical systems also need a vacuum system as the damping from background gases quickly equilibrates them with the gas's temperature. Mechanical systems usually need only one laser which is chosen for its reliability and coherence time, such as <a href="Nd%3AYAG_laser" title="Nd:YAG laser">Nd:YAG lasers</a> or <a href="Fiber_laser" title="Fiber laser">Fiber lasers</a>, as the mechanical devices are reflective over a very wide range of wavelengths.

</p>

<div class="mw-heading mw-heading3"><h3 id="Vacuum_system">Vacuum system</h3></div>

<p>In order for atoms to be laser cooled, the atoms cannot collide with room temperature background gas particles. Such collisions will drastically heat the atoms, and knock them out of weak traps. Acceptable collision rates for cold atom machines typically require vacuum pressures at 10<sup>−9</sup> Torr, and very often hundreds or even thousands of times lower pressures are necessary. To achieve these low pressures, a vacuum chamber is needed. The vacuum chamber typically includes windows so that the atoms can be addressed with lasers (e.g. for laser cooling) and light emitted by the atoms or absorption of light be the atoms can be detected. The vacuum chamber also requires an atomic source for the atom(s) to be laser cooled. The atomic source is generally heated to produce thermal atoms that can be laser cooled. For ion trapping experiments the vacuum system must also hold the ion trap, with the appropriate electric feedthroughs for the trap. Neutral atom systems very often employ a <a href="Magneto-optical_trap" title="Magneto-optical trap">Magneto-optical trap</a> (MOT) as one of the early stages in collecting and cooling atoms. For a MOT typically magnetic field coils are placed outside of the vacuum chamber to generate magnetic field gradients for the MOT.

</p>

<div class="mw-heading mw-heading3"><h3 id="Lasers">Lasers</h3></div>

<p>The <a href="Laser" title="Laser">laser</a> required for cold atom machines are entirely dependent on the choice of atom. Each atom has unique electronic transitions at very distinct wavelengths that must be driven for the atom to be laser cooled. Rubidium, for example is a very commonly used atom which requires driving two transitions with laser light at 780 nm that are separated by a few GHz. The light for rubidium can be generated from a signal laser at 780 nm and an <a href="Electro-optic_modulator" title="Electro-optic modulator">Electro-optic modulator</a>. Generally tens of mW (and often hundreds of mW to cool significantly more atoms) is used to cool neutral atoms. Trapped ions on the other hand require microwatts of optical power, as they are generally tightly confined and the laser light can be focused to a small spot size. The strontium ion, for example requires light at both 422 nm and 1092 nm in order to be Doppler cooled. Because of the small Doppler shifts involved with laser cooling, very narrow lasers, order of a few MHz, are required for laser cooling. Such lasers are generally stabilized to spectroscopy reference cells, optical cavities, or sometimes wavemeters so the laser light can be precisely tuned relative to the atomic transitions.

</p>

<ul><li><a href="List_of_laser_articles" title="List of laser articles">List of laser articles</a></li>

<li><a href="Optical_tweezers" title="Optical tweezers">Optical tweezers</a> – Scientific instruments</li>

<li><a href="Zeeman_slower" title="Zeeman slower">Zeeman Slower</a> – Instrument for slowing and cooling a beam of hot atoms</li>

<li><a href="Atomic_clock" title="Atomic clock">Atomic clock</a></li>

<li><a href="Timeline_of_low-temperature_technology" class="mw-redirect" title="Timeline of low-temperature technology">Timeline of low-temperature technology</a></li>

<li><a href="Particle_beam_cooling" title="Particle beam cooling">Particle beam cooling</a></li>

<li><a href="Quantum_refrigerators" class="mw-redirect" title="Quantum refrigerators">Quantum refrigerators</a></li>

<li><a href="M%C3%B6ssbauer_effect" title="Mössbauer effect">Mössbauer effect</a> – Resonant and recoil-free emission and absorption of gamma radiation by atomic nuclei</li>

<li><a href="M%C3%B6ssbauer_spectroscopy" title="Mössbauer spectroscopy">Mössbauer spectroscopy</a> – Spectroscopic technique</li></ul>

<div class="mw-heading mw-heading2"><h2 id="References">References</h2></div>

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<div class="mw-heading mw-heading2"><h2 id="Additional_sources">Additional sources</h2></div>

<ul><li><cite id="CITEREFMetcalfvan_der_Straten1999" class="citation book cs1">Metcalf, H. J.; van der Straten, P. (1999). <i>Laser Cooling and Trapping</i>. <a href="Springer-Verlag" class="mw-redirect" title="Springer-Verlag">Springer-Verlag</a>. <a href="ISBN_(identifier)" class="mw-redirect" title="ISBN (identifier)">ISBN</a> <bdi>978-0-387-98728-6</bdi>.</cite></li>

<li><cite id="CITEREFFoot2005" class="citation book cs1">Foot, C. J. (2005). <i>Atomic Physics</i>. Oxford University Press. <a href="ISBN_(identifier)" class="mw-redirect" title="ISBN (identifier)">ISBN</a> <bdi>978-0-19-850695-9</bdi>.</cite></li>

<li><cite id="CITEREFCohen-TannoudjiGuéry-Odelin2011" class="citation book cs1">Cohen-Tannoudji, Claude; Guéry-Odelin, David (2011). <i>Advances in Atomic Physics</i>. <a href="Doi_(identifier)" class="mw-redirect" title="Doi (identifier)">doi</a>:<a rel="nofollow" class="external text" href="https://doi.org/10.1142%2F6631">10.1142/6631</a>. <a href="ISBN_(identifier)" class="mw-redirect" title="ISBN (identifier)">ISBN</a> <bdi>978-981-277-496-5</bdi>.</cite></li>

<li><cite id="CITEREFBowleyCopeland,_Ed2010" class="citation web cs1">Bowley, Roger; Copeland, Ed (2010). <a rel="nofollow" class="external text" href="http://www.sixtysymbols.com/videos/lasercooling.htm">"Laser Cooling"</a>. <i>Sixty Symbols</i>. <a href="Brady_Haran" title="Brady Haran">Brady Haran</a> for the <a href="University_of_Nottingham" title="University of Nottingham">University of Nottingham</a>.</cite></li>

<li>PhysicsWorld series of articles by <a href="Chad_Orzel" title="Chad Orzel">Chad Orzel</a>:

<ul><li><a rel="nofollow" class="external text" href="https://physicsworld.com/a/cold-how-physicists-learned-to-manipulate-and-move-particles-with-laser-cooling/">Cold: how physicists learned to manipulate and move particles with laser cooling</a></li>

<li><a rel="nofollow" class="external text" href="https://physicsworld.com/a/colder-how-physicists-beat-the-theoretical-limit-for-laser-cooling-and-laid-the-foundations-for-a-quantum-revolution/">Colder: how physicists beat the theoretical limit for laser cooling and laid the foundations for a quantum revolution</a></li>

<li><a rel="nofollow" class="external text" href="https://physicsworld.com/a/coldest-how-a-letter-to-einstein-and-advances-in-laser-cooling-technology-led-physicists-to-new-quantum-states-of-matter/">Coldest: how a letter to Einstein and advances in laser-cooling technology led physicists to new quantum states of matter</a></li></ul></li></ul>

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</style><div id="Lasers281" style="font-size:114%;margin:0 4em"><a href="Laser" title="Laser">Lasers</a></div></th></tr><tr><td class="navbox-abovebelow" colspan="2"><div>

<ul><li><a href="List_of_laser_articles" title="List of laser articles">List of laser articles</a></li>

<li><a href="List_of_laser_types" title="List of laser types">List of laser types</a></li>

<li><a href="List_of_laser_applications" title="List of laser applications">List of laser applications</a></li>

<li><a href="Laser_acronyms" title="Laser acronyms">Laser acronyms</a></li></ul>

</div></td></tr><tr><th scope="row" class="navbox-group" style="width:1%">Types of lasers</th><td class="navbox-list-with-group navbox-list navbox-odd" style="width:100%;padding:0"><div style="padding:0 0.25em">

<ul><li><a href="Chemical_laser" title="Chemical laser">Chemical laser</a></li>

<li><a href="Dye_laser" title="Dye laser">Dye laser</a>

<ul><li><a href="Bubble_laser" title="Bubble laser">Bubble</a></li>

<li><a href="Liquid-crystal_laser" title="Liquid-crystal laser">Liquid-crystal</a></li></ul></li>

<li><a href="Gas_laser" title="Gas laser">Gas laser</a>

<ul><li><a href="Carbon_dioxide_laser" class="mw-redirect" title="Carbon dioxide laser">Carbon dioxide</a></li>

<li><a href="Excimer_laser" title="Excimer laser">Excimer</a></li>

<li><a href="Helium%E2%80%93neon_laser" title="Helium–neon laser">Helium–neon</a></li>

<li><a href="Nitrogen_laser" title="Nitrogen laser">Nitrogen</a></li></ul></li>

<li><a href="Free-electron_laser" title="Free-electron laser">Free-electron laser</a></li>

<li><a href="Laser_diode" title="Laser diode">Laser diode</a></li>

<li><a href="Solid-state_laser" title="Solid-state laser">Solid-state laser</a>

<li><a href="Raman_laser" title="Raman laser">Raman</a></li>

<li><a href="Ti-sapphire_laser" class="mw-redirect" title="Ti-sapphire laser">Ti-sapphire</a></li></ul></li>

<li><a href="X-ray_laser" title="X-ray laser">X-ray laser</a></li></ul>

</div></td></tr><tr><th scope="row" class="navbox-group" style="width:1%"><a href="Laser_science" title="Laser science">Laser physics</a></th><td class="navbox-list-with-group navbox-list navbox-even" style="width:100%;padding:0"><div style="padding:0 0.25em">

<ul><li><a href="Active_laser_medium" title="Active laser medium">Active laser medium</a></li>

<li><a href="Amplified_spontaneous_emission" title="Amplified spontaneous emission">Amplified spontaneous emission</a></li>

<li><a href="Continuous_wave" title="Continuous wave">Continuous wave</a></li>

<li><a href="Laser_ablation" title="Laser ablation">Laser ablation</a></li>

<li><a href="Laser_linewidth" title="Laser linewidth">Laser linewidth</a></li>

<li><a href="Lasing_threshold" title="Lasing threshold">Lasing threshold</a></li>

<li><a href="Population_inversion" title="Population inversion">Population inversion</a></li>

<li><a href="Ultrashort_pulse_laser" title="Ultrashort pulse laser">Ultrashort pulse</a></li></ul>

</div></td></tr><tr><th scope="row" class="navbox-group" style="width:1%">Laser optics</th><td class="navbox-list-with-group navbox-list navbox-odd" style="width:100%;padding:0"><div style="padding:0 0.25em">

<ul><li><a href="Beam_expander" title="Beam expander">Beam expander</a></li>

<li><a href="Beam_homogenizer" title="Beam homogenizer">Beam homogenizer</a></li>

<li><a href="Chirped_pulse_amplification" title="Chirped pulse amplification">Chirped pulse amplification</a></li>

<li><a href="Gain-switching" title="Gain-switching">Gain-switching</a></li>

<li><a href="Gaussian_beam" title="Gaussian beam">Gaussian beam</a></li>

<li><a href="Injection_seeder" title="Injection seeder">Injection seeder</a></li>

<li><a href="Laser_beam_profiler" title="Laser beam profiler">Laser beam profiler</a></li>

<li><a href="M_squared" title="M squared">M squared</a></li>

<li><a href="Mode_locking" title="Mode locking">Mode locking</a></li>

<li><a href="Multiple-prism_grating_laser_oscillator" title="Multiple-prism grating laser oscillator">Multiple-prism grating laser oscillator</a></li>

<li><a href="Optical_amplifier" title="Optical amplifier">Optical amplifier</a></li>

<li><a href="Optical_cavity" title="Optical cavity">Optical cavity</a></li>

<li><a href="Optical_isolator" title="Optical isolator">Optical isolator</a></li>

<li><a href="Output_coupler" title="Output coupler">Output coupler</a></li>

<li><a href="Q-switching" title="Q-switching">Q-switching</a></li></ul>

</div></td></tr><tr><td class="navbox-abovebelow" colspan="2" style="font-weight: bold;"><div>

<ul><li><span class="noviewer" typeof="mw:File"><span title="Category"></span></span> Category</li></ul>

</div></td></tr></tbody></table></div>

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</style></div><div role="navigation" class="navbox authority-control" aria-labelledby="Authority_control_databases_frameless&#124;text-top&#124;10px&#124;alt=Edit_this_at_Wikidata&#124;link=https&#58;//www.wikidata.org/wiki/Q163117#identifiers&#124;class=noprint&#124;Edit_this_at_Wikidata1017" style="padding:3px"><table class="nowraplinks hlist mw-collapsible autocollapse navbox-inner" style="border-spacing:0;background:transparent;color:inherit"><tbody><tr><th scope="col" class="navbox-title" colspan="2"><div id="Authority_control_databases_frameless&#124;text-top&#124;10px&#124;alt=Edit_this_at_Wikidata&#124;link=https&#58;//www.wikidata.org/wiki/Q163117#identifiers&#124;class=noprint&#124;Edit_this_at_Wikidata1017" style="font-size:114%;margin:0 4em">Authority control databases </div></th></tr><tr><th scope="row" class="navbox-group" style="width:1%">National</th><td class="navbox-list-with-group navbox-list navbox-odd" style="width:100%;padding:0"><div style="padding:0 0.25em"><ul><li><span class="uid"><span class="rt-commentedText tooltip tooltip-dotted" title="Laserkühlung"><a rel="nofollow" class="external text" href="https://d-nb.info/gnd/4297488-4">Germany</a></span></span></li><li><span class="uid"><span class="rt-commentedText tooltip tooltip-dotted" title="Laser cooling"><a rel="nofollow" class="external text" href="https://id.loc.gov/authorities/sh93000679">United States</a></span></span></li><li><span class="uid"><a rel="nofollow" class="external text" href="https://www.nli.org.il/en/authorities/987007546626205171">Israel</a></span></li></ul></div></td></tr><tr><th scope="row" class="navbox-group" style="width:1%">Other</th><td class="navbox-list-with-group navbox-list navbox-even" style="width:100%;padding:0"><div style="padding:0 0.25em"><ul><li><span class="uid"><a rel="nofollow" class="external text" href="https://lux.collections.yale.edu/view/concept/ff848958-655d-456c-a6db-23a41e173fd8">Yale LUX</a></span></li></ul></div></td></tr></tbody></table></div></div><div><div class="zim-footer">

This article is issued from <a class="external text" title="Last edited on 2025-07-05" href="https://en.wikipedia.org/wiki/?title=Laser_cooling&oldid=1298845932">Wikipedia</a>. The text is available under <a class="external text" href="https://creativecommons.org/licenses/by-sa/4.0/deed.en">Creative Commons Attribution-Share Alike 4.0</a> unless otherwise noted. Additional terms may apply for the media files.

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