Compact laser system for atom interferometry

Abstract

C om piled Septem ber 7,2016 W e describe an optical bench in w hich w e lock the relative frequencies or phases of a set of three lasers in order to use them in a cold atom s interferom etry experim ent. A s a new feature, the sam e tw o lasers serve alternately to cool atom s and to realize the atom ic interferom eter. T his requires a fast change of the optical frequencies over a few G H z. T he num ber of required independent laser sources is then only 3, w hich enables the construction of the w hole laser system on a single transportable optical bench. R ecent results obtained w ith this opticalsetup are also presented. c 2016 O pticalSociety ofA m erica O C IS codes: 140. 3320,120.3180,140.3550,120.3930. W i thi n the l ast decades,atom i nterferom eters have devel oped i nto a hi ghl y com peti ti ve tool for preci si on m easurem ents. 1 A tom i c fountai ns used as atom i c cl ocks are the best real i zati on of the ti m e uni t. 2 A tom i nterferom etry al so prom i sessensorsto be hi ghl y sensi ti ve to i nerti alforces. 3{6 T he use of sti m ul ated R am an transiti ons to m ani pul ate the atom i c wave packet has proven to be an e ci entway to obtai n hi gh accuracy devi ces. 5,6 In thi s l etter,we descri be a robust,com pact and versati l e l aser system for atom i nterferom eters usi ng alkal iatom s.Such experi m ents basi cal l y need two di erentopti calfrequenci es,w hose di erence rem ai nscl oseto the hyper ne transi ti on frequency.W hen they are tuned cl ose to the D 2 transi ti ons, they are used to cool and repum p the atom s i n a m agneto-opti cal trap (M O T ). W hen far detuned,and phase l ocked,they are used to i nduce sti m ul ated R am an transi ti onsforthe i nterferometer. 7 Si nce l asers are not used si m ul taneousl y for trappi ng and R am an transi ti ons, we have i m pl em ented a techni que to use the sam e two l asers for both functi ons on ourgravi m eter. 8 Ital l owed usto bui l d the w hol el aser setup on a 60 90 cm 2 opti calbench.O url asersetup i sshow n i n gure 1.A rstl aserL1 i s l ocked on an atom i c transi ti on,usi ng FM -spectroscopy 9 on a saturated absorpti on si gnal .T hi s l aser consti tutes an opti calfrequency reference and i s used i n our experi m ent to detect or push the atom s.A second l aser L2 i s al ternatel y used asrepum per orasm asterR am an l aser. Part ofthe outputs ofL1 and L2 are superi m posed on a fast photodetector (PD 12 ) (H am am atsu G 4176) and the frequency ofthe beatnote i sservo l ocked by usi ng a frequency to vol tage converter.A thi rd l aser L3 i s used al ternatel y as cool i ng or as sl ave R am an l aser.T he frequency di erence between L2 and L3 i s m easured w i th a second opti cal beat note on PD 23 . Fi nal l y, both L2 and L3 beam s are superi m posed and di rected through an acousto-opti calm odul atorei therto a m agneto-opti cal trap or to an atom i c i nterferom eter.B oth frequency l ocks of L2 and L3 use the sam e schem e w hi ch i sshow n i n gure 2.T he opti calbeatnote i ssued from the photode...

Influence of lasers propagation delay on the sensitivity of atom interferometers

“…The intensity of the lasers is then adiabatically decreased to drop the atoms, and we detune both the repumper and cooling lasers from the atomic transitions by about 1 GHz to obtain the two off-resonant Raman lasers. A description of the compact and agile laser system that we developed can be found in [24]. The preparation sequence ends with the selection of a narrow velocity distribution (σ v ≤ v r = 5.9mm/s) in the |F = 1, m F = 0 state, using a combination of microwave and optical pulses.…”

“…Indeed, the PLL noise contributes for 2.1 mrad/shot [26], the various frequency references for 1.6 mrad/shot [24], and the propagation in the optical fiber for 1.0 mrad/shot. All these noise sources are independent, so the frequency noise of the Raman lasers represents a total contribution of σ Φ = 3.7 mrad/shot to the interferometer phase sensitivity.…”

Double diffraction in an atomic gravimeter

“…The experiment was carried out in the gravimeter setup described in detail in [3,19]. In this compact experimental set-up, cold 87 Rb atoms are first trapped in a 3D MOT during 300 ms. With respect to [3] where a 2D MOT was used, atoms are loaded directly from a background Rb vapor.…”

Off-resonant Raman transition impact in an atom interferometer

“…This effect thus depends on the actual trajectories of the atoms, so that a precise control of the initial position, velocity and temperature of the atomic clouds is required [12,13]. A convenient technique to reduce this bias is to minimize the number of optical components in the shaping of the two Raman laser beams and by implementing them in a retro-reflected geometry [1,3,14]. Indeed, as long as the two beams travel together, wave-front aberrations are identical for the two beams and thus have no influence on their phase difference.…”