DOCSLIB.ORG

Three-Dimensional Laser Cooling at the Doppler Limit R

Total Page：16

File Type：pdf, Size：1020Kb

Download full-text PDF Read full-text
Three-Dimensional Laser Cooling at the Doppler Limit R Three-dimensional laser cooling at the Doppler limit R. Chang, A. L. Hoendervanger, Q. Bouton, Y. Fang, T. Klafka, K. Audo, Alain Aspect, C. I. Westbrook, D. Clément To cite this version: R. Chang, A. L. Hoendervanger, Q. Bouton, Y. Fang, T. Klafka, et al.. Three-dimensional laser cooling at the Doppler limit. Physical Review A, American Physical Society, 2014, 90 (6), pp.063407. 10.1103/PhysRevA.90.063407. hal-01068704 HAL Id: hal-01068704 https://hal.archives-ouvertes.fr/hal-01068704 Submitted on 22 Feb 2015 HAL is a multi-disciplinary open access L’archive ouverte pluridisciplinaire HAL, est archive for the deposit and dissemination of sci- destinée au dépôt et à la diffusion de documents entific research documents, whether they are pub- scientifiques de niveau recherche, publiés ou non, lished or not. The documents may come from émanant des établissements d’enseignement et de teaching and research institutions in France or recherche français ou étrangers, des laboratoires abroad, or from public or private research centers. publics ou privés. Copyright Three-Dimensional Laser Cooling at the Doppler limit R. Chang,1 A. L. Hoendervanger,1 Q. Bouton,1 Y. Fang,1, 2 T. Klafka,1 K. Audo,1 A. Aspect,1 C. I. Westbrook,1 and D. Cl´ement1 1Laboratoire Charles Fabry, Institut d'Optique, CNRS, Univ. Paris Sud, 2 Avenue Augustin Fresnel 91127 PALAISEAU cedex, France 2Quantum Institute for Light and Atoms, Department of Physics, State Key Laboratory of Precision Spectroscopy, East China Normal University, Shanghai, 200241, China Many predictions of Doppler cooling theory of two-level atoms have never been verified in a three- dimensional geometry, including the celebrated minimum achievable temperature ~Γ=2kB , where Γ is the transition linewidth. Here, we show that, despite their degenerate level structure, we can use Helium-4 atoms to achieve a situation in which these predictions can be verified. We make measurements of atomic temperatures, magneto-optical trap sizes, and the sensitivity of optical molasses to a power imbalance in the laser beams, finding excellent agreement with Doppler theory. We show that the special properties of Helium, particularly its small mass and narrow transition linewidth, prevent effective sub-Doppler cooling with red-detuned optical molasses. I. INTRODUCTION 35 30 The seminal proposals for Doppler cooling in 1975 [1,2] 25 prompted the realization of the first optical molasses in D the 1980's [3], a major landmark in the field of laser cool- [ T ] 20 ing and trapping of atoms [4{6]. The physical concepts behind the Doppler cooling mechanism are both simple 15 10 MOT temperature and elegant, and predict the achievement of very low tem- Temperature peratures. They remain to this day the starting point of Molasses temperature Doppler theory I=I most courses on laser cooling and degenerate gases [7]. It 5 MOT Doppler theory I=IMOL is thus ironic that not only, to our knowledge, quantita- 0 tive predictions of this simple model have not been exper- -30 -25 -20 -15 -10 -5 0 Detuning [ Γ ] imentally validated, but moreover, experimental studies have found results quantitatively and even qualitatively 4.0 different from the predictions of the model [8{11]. Today, it is well known that for most atoms with a 3.5 degenerate ground state manifold, the complex multi- D 3.0 level structure gives rise to new mechanisms which come [ T ] to dominate the cooling process, yielding ultimate tem- 2.5 peratures far below those predicted by Doppler theory [7, 12, 13]. Accounting for these sub-Doppler mecha- 2.0 nisms allows one to understand the qualitative and quan- Temperature titative experimental observations. In contrast, three- 1.5 dimensional laser cooling of an atomic sample in agree- 1.0 ment with the celebrated Doppler model is still lack- -2.0 -1.5 -1.0 -0.5 0.0 ing [14]. Recent work with alkaline-earth and rare-earth Detuning [ Γ ] atoms, which exhibit a non-degenerate ground state, have provided natural candidates to study cooling in a purely FIG. 1. Temperature in magneto-optical trap and optical Doppler regime. Yet, to our knowledge, all experiments molasses as a function of the detuning of the laser cooling with these atoms have found temperatures above the ex- beams. Temperatures are extracted from monitoring time-of- pected Doppler limit in magneto-optical traps (MOTs) flight expansion of the gas. Error bars (one standard de- [16{28]. This discrepancy has been attributed to the viation) reflect the error from fitting. The total intensity presence of additional heating mechanism [29, 30]. (sum of the six beams) used in the experiment are respec- Here we report the three-dimensional laser cooling of tively IMOT = 100 Isat and IMOL = Isat=10. The lines are the metastable Helium-4 gases in the Doppler regime. We results of Doppler theory of Eq.7, for intensities IMOT (solid line) and I (dashed line). monitor the temperature of the gas as a function of MOL the laser detuning δ, as shown in Fig.1, finding excel- lent agreement with Doppler theory. The temperature reaches a minimum for a detuning δ = −Γ=2 (where Γ is the transition linewidth), while increasing with jδj at val- ues jδj Γ, in contrast with sub-Doppler molasses. In 2 addition, the drift velocities of optical molasses with un- the temperature of a 3D molasses formed by three or- balanced power between counter-propagating beams are thogonal pairs of counter-propagating laser beams is, far larger than those expected of sub-Doppler molasses 3 3 Γ 1 + I =I + (2δ=Γ)2 [9]. We use the 2 S1 ! 2 P2 transition of Helium-4, ~ tot sat kBT2level = ; (3) which allows in principle for sub-Doppler cooling, and 2 4jδj=Γ yet our results show no evidence for such effects. We where the I = 6I is the total intensity resulting from present a physical argument showing that the special tot all six laser beams. In the Doppler regime, the minimum properties of metastable Helium (4He*) strongly inhibit possible temperature is achieved for a detuning δ = −Γ=2 sub-Doppler cooling in the experimental configuration we and vanishing intensity. This minimum is commonly re- probe. ferred to as the Doppler limit, TD = ~Γ=2kB . We now turn the discussion to an atom with sev- II. THEORETICAL CONSIDERATIONS eral ground-state levels where sub-Doppler mechanisms of cooling may be involved [9, 10, 12]. For this discussion we restrict ourselves to the atomic structure of the 4He* A. Laser cooling mechanisms 3 3 atom on the 2 S1 ! 2 P2 transition (see Fig.2a), and the laser configuration used in the experiment: counter- Laser cooling of an atomic gas relies upon the ex- propagating laser beams with opposite circular polariza- change of momentum between the atoms and the near- tion (configuration σ+ −σ−) along three orthogonal axes. resonant light field, resulting in a mechanical force F on Consider first a single axis of the system. Following the atoms. For small velocities, the equilibrium temper- the derivation from [31] an explicit formulation of the ature T of these cooling schemes is given by the ratio of a semi-classical force F on a moving atom can be obtained. momentum-space diffusion constant D (given by the fluc- This approach takes into account atomic coherence ef- tuations of the force) to the velocity-damping coefficient fects up to second-order in absorption-emission processes. α. In the following we will first recall the main theoreti- In Fig.2 we plot this force F along with that exerted on cal results for laser Doppler cooling of a two-level atom, a two-level atom F2level. In the low-velocity region (see then proceeding to discuss a multi-level atom where sub- Fig.2c) the cooling force on the multi-level atom ex- Doppler mechanisms may appear. hibits a sharp feature with an associated damping coeffi- The mechanical interaction of a near-resonant light cient α significantly larger than that of a two-level atom. beam (frequency !) with a two-level atom (atomic reso- This feature arises from the presence of atomic coher- nance frequency !0) is dominated by the radiation pres- ences and two-photon processes, and is the signature of sure effect and its associated force [9]. This light-matter sub-Doppler cooling mechanisms. Since the momentum- interaction is characterised by the laser detuning from space diffusion coefficient hardly changes, the new damp- resonance δ = ! − !0, the laser intensity I, the natural ing coefficient would lead one to expect sub-Doppler cool- linewidth of the transition Γ, and the saturation intensity ing. of the transition Isat. A convenient physical quantity is In this configuration, the additional cooling results the generalized saturation parameter from a motion-induced population difference between the s ground-state levels, and is referred to as σ+ − σ− polar- s = 0 ; (1) 1 + 4δ2=Γ2 ization gradient cooling. In a 3D configuration, it is well known that Sisyphus cooling can also occur due to spa- which characterizes the excited state population in a 2- tially dependent light shifts of the atomic ground-state 2 2 level atom, s=2(1 + s). Here s0 = I=Isat = 2Ω =Γ is the levels. The electric field from laser beams along orthog- on-resonance saturation parameter, and Ω is the Rabi onal axes interfere, resulting in a modulation of the in- frequency. tensity, which in turn may lead to Sisyphus cooling as At low saturation of the atomic transition s 1 and in a one-dimensional lin ? lin configuration. Within the small velocities jkvj jδj, the average force acting on parameter range of interest (jδj ∼ Γ), both sub-Doppler a two-level atom moving at velocity v takes the form effects result in similar velocity capture ranges and equi- F2level = −α2levelv with librium temperatures [9, 10, 12].
Load more

Recommended publications
  • Graduate Studies in Nuclear Physics At
    Graduate Studies in Atomic, Molecular, and Optical Physics at The College of William and Mary Atomic, Molecular, and Optical Group: General Information: Experimental Faculty: 4 The College of William and Mary (W&M), chartered in 1693, Theoretical Faculty: 1 is the second oldest university in the US. It boasts four US Graduate Students: 14 presidents, supreme court justices and Jon Stewart as alumni. Female Students: 5 W&M is a liberal arts university with a strong research focus. Our 7,800 students (2,000 of them graduate students) enjoy a Rankings (US News and World Report): low student-to-faculty ratio, state-of-the-art facilities, and a beautiful campus. W&M ranked 6th amongst public US universities Located in Williamsburg, Virginia, W&M is in the heart of Physics Department Statistics: colonial American history and is adjacent to Colonial Average annual number of Ph. D. recipients: 8 Williamsburg, a historic recreation of 18th century colonial Average time to Ph. D.: 5 years life. While much of the campus has been restored to its 18th- century appearance, the physics department is housed in a Departmental Website: newly refurbished and expanded building that provides http://www.wm.edu/physics outstanding teaching and research space. http://www.wm.edu/as/physics/research/index.php The William and Mary physics department benefits Graduate Admissions: enormously from close ties with both Thomas Jefferson http://www.wm.edu/as/physics/grad/index.php National Accelerator Facility (JLab) and NASA Langley Application deadline: Feb 1st Research Center in nearby Newport News (thirty minutes from the W&M campus).
    [Show full text]
  • Laser Cooling and Trapping Lecture 1 Light Forces Lecture 2 Doppler
    Laser cooling and trapping Lecture 1 Light forces Lecture 2 Doppler cooling Lecture 3 Sub-Doppler cooling Lecture 4 Magneto-optical trap Evaporative cooling How cold? 100 K 1 mK 77 K Liquid N2 10 K 100 µK 4 K Liquid 4He Laser cooling 1 K 10 µK 1 µK 100 mK 30 mK Dilution Bose – Einstein 10 mk refrigerator 100 nK condensate (Record : 500 pK) (Very…) short history Sub-Doppler cooling Beam slowing 1982 1988 Sub-recoil cooling 1980 1985 1990 1997 Optical molasses 1975 Hänsch, Schalow Demhelt, Wineland 1980 S. Chu W. Phillips C. Cohen- Gordon, Ashkin Tannoudji Zeeman slowing Slowed atoms Initial distribution Phillips, PRL 48, p. 596 (1982) Crossed dipole trap – crystal of light Optical lattices 1 - d 2 - d 3 - d (M. Greiner) Optical tweezers: trapping in 3 D High field seekers ω < ω0 Gaussian beam ~ ~ α Diffraction limited optics w ~ λ Trapping volume ~ π λ3 NA = sin α Ex: 1 mW on 1 µm w ~ λ/NA Trap depth = 1 mK Detecting a single atom CCD 5 µm 12 8 4 counts / ms 0 0 5 10 15 20 25 time (sec) Institut d’Optique, France Guiding an atom laser Institut d’Optique, France Bouncing atoms on a surface Institut d’Optique, 1996 3D optical molasses Chu (1985) Laser cooling and Maxwell Boltzman distribution Lett et al., JOSA B 11, p. 2024 (1989) The results of Phillips et al. (1988) Time-of-flight measurement Doppler theory For Na, TD = 240 µK Lett, PRL 61, p. 169 (1988) Laser cooled atoms (2010) Laser cooled atoms (2010) Discovery of sub-Doppler cooling (1988) Time-of-flight measurement Doppler theory For Na, TD = 240 µK Lett, PRL 61, p.
    [Show full text]
  • Direct Frequency Comb Laser Cooling and Trapping
    Selected for a Viewpoint in Physics PHYSICAL REVIEW X 6, 041004 (2016) Direct Frequency Comb Laser Cooling and Trapping A. M. Jayich,* X. Long, and W. C. Campbell Department of Physics and Astronomy, University of California, Los Angeles, Los Angeles, California 90095, USA and California Institute for Quantum Emulation, Santa Barbara, California 93106, USA (Received 11 May 2016; published 10 October 2016) Ultracold atoms, produced by laser cooling and trapping, have led to recent advances in quantum information, quantum chemistry, and quantum sensors. A lack of ultraviolet narrow-band lasers precludes laser cooling of prevalent atoms such as hydrogen, carbon, oxygen, and nitrogen. Broadband pulsed lasers can produce high power in the ultraviolet, and we demonstrate that the entire spectrum of an optical frequency comb can cool atoms when used to drive a narrow two-photon transition. This multiphoton optical force is also used to make a magneto-optical trap. These techniques may provide a route to ultracold samples of nature’s most abundant building blocks for studies of pure-state chemistry and precision measurement. DOI: 10.1103/PhysRevX.6.041004 Subject Areas: Atomic and Molecular Physics I. INTRODUCTION ultraviolet means that laser cooling and trapping is not currently available for the most prevalent atoms in organic High-precision physical measurements are often under- chemistry: hydrogen, carbon, oxygen, and nitrogen. taken close to absolute zero temperature to minimize Because of their simplicity and abundance, these species, thermal fluctuations. For example, the measurable proper- with the addition of antihydrogen, likewise play prominent ties of a room temperature chemical reaction (rate, roles in other scientific fields such as astrophysics [11] and product branching, etc.) include a thermally induced precision measurement [12], where the production of average over a large number of reactant and product cold samples could help answer fundamental outstanding quantum states, which masks the unique details of questions [13–15].
    [Show full text]
  • Laser Cooling of Two Trapped Ions: Sideband Cooling Beyond the Lamb-Dicke Limit
    PHYSICAL REVIEW A VOLUME 59, NUMBER 5 MAY 1999 Laser cooling of two trapped ions: Sideband cooling beyond the Lamb-Dicke limit G. Morigi,1 J. Eschner,2 J. I. Cirac,1 and P. Zoller1 1Institut fu¨r Theoretische Physik, Universita¨t Innsbruck, A-6020 Innsbruck, Austria 2Institut fu¨r Experimentalphysik, Universita¨t Innsbruck, A-6020 Innsbruck, Austria ~Received 8 December 1998! We study laser cooling of two ions that are trapped in a harmonic potential and interact by Coulomb repulsion. Sideband cooling in the Lamb-Dicke regime is shown to work analogously to sideband cooling of a single ion. Outside the Lamb-Dicke regime, the incommensurable frequencies of the two vibrational modes result in a quasicontinuous energy spectrum that significantly alters the cooling dynamics. The cooling time decreases nonlinearly with the linewidth of the cooling transition, and the effect of dark states which may slow down the cooling is considerably reduced. We show that cooling to the ground state is also possible outside the Lamb-Dicke regime. We develop the model and use quantum Monte Carlo calculations for specific examples. We show that a rate equation treatment is a good approximation in all cases. @S1050-2947~99!11605-6# PACS number~s!: 32.80.Pj, 42.50.Vk, 03.67.Lx I. INTRODUCTION sideband cooling of two ions to the ground state has been achieved in a Paul trap that operates in the Lamb-Dicke limit The emergence of schemes that utilize trapped ions or @11#. However in this experiment the Lamb-Dicke regime atoms for quantum information, and the interest in quantum required such a high trap frequency that the distance between statistics of ultracold atoms, have provided renewed interest the ions does not allow their individual addressing with a and applications for laser cooling techniques @1#.
    [Show full text]
  • Laser Cooling Yb + Ions with an Optical Frequency Comb
    UNIVERSITY OF CALIFORNIA Los Angeles Laser cooling Yb+ ions with optical frequency comb A dissertation submitted in partial satisfaction of the requirements for the degree Doctor of Philosophy in Physics by Michael Ip 2018 c Copyright by Michael Ip 2018 ABSTRACT OF THE DISSERTATION Laser cooling Yb+ ions with optical frequency comb by Michael Ip Doctor of Philosophy in Physics University of California, Los Angeles, 2018 Professor Wesley C. Campbell, Chair Trapped atomic ions are a multifaceted platform that can serve as a quan- tum information processor, precision measurement tool and sensor. How- ever, in order to perform these experiments, the trapped ions need to be cooled substantially below room temperature. Doppler cooling has been a tremendous work horse in the ion trapping community. Hydrogen-like ions are good candidates because they have typically have a simple closed cycling transition that requires only a few lasers to Doppler cool. The 2S to 2P transition for these ions however typically lies in the UV to deep UV regime which makes buying a standard CW laser difficult as optical power here is hard to come by. Rather using a CW laser, which requires frequency stabilization and produces low optical power, this thesis explores how a mode-locked laser in the comb regime Doppler cools Yb ions. This thesis explores how a mode-locked laser is able to laser cool trapped ions and the consequences of using a broad spectrum light source. I will first give an overview of the architecture of our oblate Paul trap. Then I will discuss how a 10 picosecond optical pulse with a repetition rate of 80 MHz 2 2 interacts with a 20 MHz linewidth S1=2 to P1=2 transition.
    [Show full text]
  • Infrared Comb Spectroscopy of Buffer-Gas-Cooled Molecules: Toward Absolute Frequency Metrology of Cold Acetylene
    International Journal of Molecular Sciences Review Infrared Comb Spectroscopy of Buffer-Gas-Cooled Molecules: Toward Absolute Frequency Metrology of Cold Acetylene Luigi Santamaria 1 , Valentina Di Sarno 2,3, Roberto Aiello 2,3, Maurizio De Rosa 2,3, Iolanda Ricciardi 2,3, Paolo De Natale 4,5 and Pasquale Maddaloni 2,3,* 1 Agenzia Spaziale Italiana, Contrada Terlecchia, 75100 Matera, Italy; [email protected] 2 Consiglio Nazionale delle Ricerche-Istituto Nazionale di Ottica, Via Campi Flegrei 34, 80078 Pozzuoli, Italy; [email protected] (V.D.S.); [email protected] (R.A.); [email protected] (M.D.R.); [email protected] (I.R.) 3 Istituto Nazionale di Fisica Nucleare, Sez. di Napoli, Complesso Universitario di M.S. Angelo, Via Cintia, 80126 Napoli, Italy 4 Consiglio Nazionale delle Ricerche-Istituto Nazionale di Ottica, Largo E. Fermi 6, 50125 Firenze, Italy; [email protected] 5 Istituto Nazionale di Fisica Nucleare, Sez. di Firenze, Via G. Sansone 1, 50019 Sesto Fiorentino, Italy * Correspondence: [email protected] Abstract: We review the recent developments in precision ro-vibrational spectroscopy of buffer-gas- cooled neutral molecules, obtained using infrared frequency combs either as direct probe sources or as ultra-accurate optical rulers. In particular, we show how coherent broadband spectroscopy of complex molecules especially benefits from drastic simplification of the spectra brought about by cooling of internal temperatures. Moreover, cooling the translational motion allows longer light-molecule interaction times and hence reduced transit-time broadening effects, crucial for high- precision spectroscopy on simple molecules.
    [Show full text]
  • Redalyc.Interferometry with Large Molecules: Exploration Of
    Brazilian Journal of Physics ISSN: 0103-9733 [email protected] Sociedade Brasileira de Física Brasil Arndt, Markus; Hackermüller, Lucia; Reiger, Elisabeth Interferometry with large molecules: Exploration of coherence, decoherence and novel beam methods Brazilian Journal of Physics, vol. 35, núm. 2A, june, 2005, pp. 216-223 Sociedade Brasileira de Física Sâo Paulo, Brasil Available in: http://www.redalyc.org/articulo.oa?id=46435204 How to cite Complete issue Scientific Information System More information about this article Network of Scientific Journals from Latin America, the Caribbean, Spain and Portugal Journal's homepage in redalyc.org Non-profit academic project, developed under the open access initiative 216 Brazilian Journal of Physics, vol. 35, no. 2A, June, 2005 Interferometry with Large Molecules: Exploration of Coherence, Decoherence and Novel Beam Methods Markus Arndt, Lucia Hackermuller,¨ and Elisabeth Reiger Institut fur¨ Experimentalphysik, Universitat¨ Wien, Boltzmanngasse 5 Received on 25 January, 2005 Quantum experiments with complex objects are of fundamental interest as they allow to quantitatively trace the quantum-to-classical transition under the influence of various interactions between the quantum object and its environment. We briefly review the present status of matter wave interferometry and decoherence studies with large molecules and focus in particular on the challenges for novel beam methods for molecular quantum optics with clusters, macromolecules or nanocrystals. I. INTRODUCTION a) Slitsource Diffraction Scanning array grating mask Recent years have seen tremendous progress in experiments demonstrating the very foundations of quantum physics with systems of rather large size and complexity. The present arti- G G G cle focuses on matter wave interferometry, which clearly vi- 1 2 3 sualizes the essence of the quantum superposition principle b) Collisionswith for position states of massive particles.
    [Show full text]
  • Advances in Laser Slowing, Cooling, and Trapping Using Narrow Linewidth Optical Transitions
    Advances in Laser Slowing, Cooling, and Trapping using Narrow Linewidth Optical Transitions by John Patrick Bartolotta B.S., University of Connecticut, 2014 M.S., University of Connecticut, 2016 A thesis submitted to the Faculty of the Graduate School of the University of Colorado in partial fulfillment of the requirements for the degree of Doctor of Philosophy Department of Physics 2021 ii Bartolotta, John Patrick (Ph.D., Physics) Advances in Laser Slowing, Cooling, and Trapping using Narrow Linewidth Optical Transitions Thesis directed by Prof. Murray J. Holland Laser light in combination with electromagnetic traps has been used ubiquitously throughout the last three decades to control atoms and molecules at the quantum level. Many approaches with varying degrees of reliance on dissipative processes have been discovered, investigated, and implemented in both academic and industrial settings. In this thesis, we theoretically investigate and propose three practical techniques which have the capacity to slow, cool, and trap particles with narrow linewidth optical transitions. Each of these methods emphasizes a high degree of coherent control over quantum states, which lends their operation a reduced reliance on spontaneous emission and thus makes them appealing candidates for application to systems that lack closed cycling transitions. In a more general setting, we also study the transfer of entropy from a quantum system to a classically-behaved coherent light field, and therefore advance our understanding of the role of dissipative processes in optical pumping and laser cooling. First, we describe theoretically a cooling technique named \sawtooth wave adiabatic passage cooling," or \SWAP cooling," which was discovered experimentally at JILA and has since been implemented elsewhere with various atomic species.
    [Show full text]
  • Millikelvin Cooling of an Optically Trapped Microsphere in Vacuum
    Millikelvin cooling of an optically trapped microsphere in vacuum Tongcang Li, Simon Kheifets, and Mark G. Raizen Center for Nonlinear Dynamics and Department of Physics, The University of Texas at Austin, Austin, TX 78712, USA The apparent conflict between general relativity and quantum mechanics remains one of the unresolved mysteries of the physical world1,2. According to recent theories2-4, this conflict results in gravity-induced quantum state reduction of “Schrödinger cats”, quantum superpositions of macroscopic observables. In recent years, great progress has been made in cooling micromechanical resonators towards their quantum mechanical ground state5-12. This work is an important step towards the creation of Schrödinger cats in the laboratory, and the study of their destruction by decoherence. A direct test of the gravity-induced state reduction scenario may therefore be within reach. However, a recent analysis shows that for all systems reported to date, quantum superpositions are destroyed by environmental decoherence long before gravitational state reduction takes effect13. Here we report optical trapping of glass microspheres in vacuum with high oscillation frequencies, and cooling of the center-of-mass motion from room temperature to a minimum temperature of 1.5 mK. This new system eliminates the physical contact inherent to clamped cantilevers, and can allow ground-state cooling from room temperature14-20. After cooling, the optical trap can be switched off, allowing a microsphere to undergo free-fall in vacuum20. During free-fall, light scattering and other sources of environmental decoherence are absent, so this system is ideal for studying gravitational state reduction21. A cooled optically trapped object in vacuum can also be used to search for non-Newtonian gravity forces at small scales22, measure the impact of a single air molecule19, and even produce Schrödinger cats of living organisms14.
    [Show full text]
  • Cool Things You Can Do with Lasers
    Cool Things you can do with Lasers Aidan Arnold A thesis submitted for the degree of Master of Science at the University of Otago, Dunedin, New Zealand August 19, 1996 i Abstract Theoretical and experimental investigations into a variety of laser cooling phenomena are presented. An overview of the history of laser cooling is followed by an in-depth study of analytic Doppler theory, as applied to both MOTs and optical molasses. The 3D distributions of Gajda et al. [27] are generalised, allowing the inclusion of both intensity and frequency imbalances. Forces arising from reradiation and absorption are then added to the description, with particular em- phasis on the non-conservative absorptive force. Constant-temperature solutions do not appear to exist for the di®erential equations which arise in such a regime, raising questions about the validity of commonly used density relations based on this assumption. Possible errors in the formalism are covered, as well as their means of recti¯cation. Work on the theoretical Doppler forces involved in ring-shaped MOT structures is reviewed, and possible solutions to the present discrepancy between theoretical and experimental studies in this ¯eld are discussed in the context of reradiation. Analytic theory as well as a Doppler Monte Carlo simulation are employed. A brief description of sub-Doppler theory is succeeded by a theoretical study of the 3D standing waves in laser cooling apparatus, focusing on the relative phases of the laser beams. Properties of various laser polarisation con¯gurations are discussed with respect to the Sisyphus parameter p; of Steane et al.
    [Show full text]
  • Laser Cooling and Trapping of Neutral Calcium Atoms
    Laser Cooling and Trapping of Neutral Calcium Atoms Ian Norris A thesis presented in partial fulfillment of the requirements for the degree of Doctor of Philosophy Department of Physics University of Strathclyde August 2009 This thesis is the result of the author's original research. It has been composed by the author and has not been previously submitted for examination which has lead to the award of a degree. The copyright of this thesis belongs to the author under the terms of the United Kingdom Copyright Acts as qualified by University of Strathclyde Reg- ulation 3.50. Due acknowledgement must always be made of the use of any material contained in, or derived from, this thesis. Signed: Date: Laser Cooling and Trapping of Neutral Calcium Atoms Ian Norris Abstract This thesis presents details on the design and construction of a compact magneto- optical trap (MOT) for neutral calcium atoms. All of the apparatus required to successfully cool and trap ∼106 40Ca atoms to a temperature of ∼3 mK are described in detail. A new technique has been developed for obtaining dispersive saturated ab- sorption signal using a hollow-cathode lamp. The technique is sensitive enough to detect signals produced by isotopes of calcium with abundances of less than 0.2 %. A compact Zeeman slower has been used to reduce the velocity of a thermal beam of calcium atoms to around 60 m/s, which are then deflected into a MOT using resonant light. A discussion on the characterisation and optimisation of the Zeeman slower and deflection stage is also given.
    [Show full text]
  • ECE 493-Lasers
    Lasers L.A.S.E.R. LIGHT AMPLIFICATION by STIMULATED EMISSION of RADIATION History of Lasers and Related Discoveries 1917 Stimulated emission proposed by Einstein 1947 Holography (Gabor, Physics Nobel Prize 1971) 1954 MASER (Townes, Basov, Prokhorov, Physics Nobel Prize 1964) but 1 st maser constructed by Maiman in 1960 1958 LASER: optical maser (Laser spectroscopy by Schawlow, Bloembergen, Physics Nobel Prize 1981) 1960 Ruby Laser: 1 st laser 1963 Semiconductor heterostructures (Alferov, Kroemer, Physics Nobel Prize 2000) 1970 Corning glass (optical fiber) 1980 Laser cooling of atoms (Chu, Cohen-Tannoudki, Phillips, Physics Nobel Prize 1997) Applications of Lasers CD Countermeasures DVD Dazzler Blu-Ray Surgery Bar code Laser welding Internet Engraving Laser pointer Curing (dentistry) Laser sight (targeting) Optical tweezer Speed measurement Laser printing Laser distance meter Alignment LIDAR (light detection and Holography ranging) Laser bonding Projection display Free space communications Spectroscopy (Raman, PL…) Microscopy WHAT ELSE, WHAT CAN YOU Laser cooling ADD TO THE LIST? … Nuclear fusion Spectral Range of Existing Lasers Types of Lasers Gas Lasers (1 m) Solid State Lasers (1 cm) Semiconductor (Diode) Lasers (1 µm) Types of Lasers Continuous Wave Operation Pulse Mode Operation Pout Pout Pulse width Ppeak 0t 0 t Period • Higher peak powers • Duty cycle (%) • Average powers Green Laser Pointer • Green light is from frequency doubling (2 photons combine energy into 1) • More generally: non linear optical effects i.e. add or subtract frequencies How a CD/DVD Laser Works http://micro.magnet.fsu.edu/primer/java/lasers/compactdisk/index.html Fundamentals of Lasers Consider a two-level system (excited level state and ground level state).
    [Show full text]