Atom Interferometry with Mg Beams

Transcription

1 Laser Physics, Vol. 11, No. 11, 21, pp Original Text Copyright 21 by Astro, Ltd. Copyright 21 by MAIK Nauka /Interperiodica (Russia). ATOMIC INTERFEROMETRY AND LITOGRAPHY, CAVITY QED Atom Interferometry with Mg Beams S. N. Bagayev, V. I. Baraulia, A. E. Bonert, A. N. Goncharov, M. R. Seydaliev, and A. S. Tychkov Institute of Laser Physics, Siberian Division, Russian Academy of Sciences, pr. Lavrent eva 13/3, Novosibirsk, 639 Russia Received April 1, 21 Abstract We developed the laser system at 457 nm based on cw ring Ti:Sap laser and enhanced cavity SHG in LBO and KN crystals with linewidth <3 khz for interferometry experiments with Mg atomic beam. For laser cooling and deflection of Mg beam the laser system at 285 nm based on ring R6G cw dye laser and SHG in BBO nonlinear crystal has been realized. The results of Mg interferometry experiments in four-beam Bordé geometry are presented as well as the results of Zeeman cooling experiments in transverse magnetic field. The zero order interference fringes correspondent to the recoil doublet were detected with the resolution of ~3 khz. The Mg beam with the flux of ~1 11 atoms/s, the mean velocity of ~2 m/s and the width of velocity distribution of ~5 m/s (FWHM) was produced. INTRODUCTION The key problem for building up the real atom interferometer was the difficulties to create optical elements like mirrors and splitters for atoms. Last decade fast progress in nanofabrication technology and atom optics results in the development of such elements for atoms based both on diffraction gratings (slits) and coherent interaction between light and atoms. As a result, macroscopic atomic and molecular interferometers were built up at the beginning of the 199s (for overview of atom interferometry see [1]). The most promising applications of an atom interferometry are high precision studies of atomic and molecular properties and weak interactions of atoms (molecules) with environment fields, other atoms, molecules and surfaces. Precision tests of physical theories and precise determination of the fundamental constants are possible with high sensitive atomic interferometers. Atomic interferometers based on cooled atoms are very promising as high sensitive inertial sensors for measurements of acceleration, rotation and gravity. The present paper is dealing with the atom interferometer based on resonant laser light splitter and recombiner. This type of an interferometer directly connected with ultrahigh resolution laser spectroscopy in separated fields [2]. For the first time three standing wave separated fields geometry of an atom interferometer was proposed in [3]. If the coherent interaction between atoms and resonant laser light are used in order to split and recombine an atomic wave then the phase of interference patterns depends strongly on the light frequency. This type of an interferometer is very promising for new type of optical frequency standards and precise measurements of fundamental constants we are interested in. In 1989 Ch. Borde proposed the geometry of an atom interferometer consisted of two pairs of running laser fields [4] advanced in better its physical interpretation as well as higher contrast of interference patterns in comparison with three standing wave geometry. The scheme of this so called Borde interferometer is shown in Fig. 1. Here we assume two levels atoms (a-lower level, b-upper level) interacting with resonant laser fields at frequency ν ω ab /2π. First beam serves as coherent splitter for an atomic wave. Atom can absorb photon with probability depending on the power of the laser beam, the duration of the interaction and detuning of the laser frequency from ω ab. This interaction changes not only the internal state of an atom but also transfers the momentum equal to 1 (in the units of k) in the direction of the laser beam due to the recoil effect. So, between the first and the second beams an atom is in the coherent superposition of two states (a, ) and (b, 1). The second laser beam acts as a mirror for atomic wave an atom in (b, 1) state can coherently irradiate a Laser beams z x Laser beams b, 1 Atomic a, a, a, beam d b, 1 b, 1 a, Fig. 1. Schematic diagram of four-beam Bordé interferometer. 1178

2 ATOM INTERFEROMETRY WITH Mg BEAMS 1179 photon when interacts with the second beam and return back to the state (a, ). Note that to keep the coherency of this process the time of flight T between the laser beams has to be shorter then life time of the state b. The third and the fourth laser beams act as a mirror and recombiner for atomic wave. The closed area between two arms may be treated as Mach Zehnder atom interferometer. For simplicity, only one of two possible closed area interferometers is depicted in Fig. 1. Because of a de Broglie wavelength (a few tens of picometers) is much shorter than a wavelength of light the diffraction angle of an atom is rather small (a few microradians). Usually an interferometer arms separation in the space (a few micron) is smaller then an atomic beam diameter. Nevertheless, one can observe an interferometry patterns due to the internal state labeling of an interferometer outputs that is the advantage of this interferometer type. As space resolution of interferometer arms is very important to carry out some principal experiments and because of an interferometer sensitivity increases with it s square, the spatial resolution of interferometer s arms as well as the enlargement of arm s separation are the key questions for atom interferometry. The arm s separation limit is equal to d τh/λm, where τ is the life time of an atom upper state, h is the Plank constant, λ is the wavelength of light used in the interferometer, m is the mass of the atom. In order to have large area of an interferometer and macroscopic arm s separation it s better to use narrow optical transitions of light atoms in the visible and ultraviolet ranges. The level schemes of light alkaline earth elements as Mg and Ca are promising for frequency standards [5] and atom interferometry. The intercombination narrow transitions 1 S 3 P 1 are very useful for atomic wave splitters and recombiners as well as fast 1 S P 1 transitions may be used for laser cooling of an atomic beams. The interferometer with Ca atoms was developed in 1991 [6] as well as Mg interferometer was built up in 1992 [7] (see also [1, pp ]). Mg has some advantages in comparison to Ca resulting in 2 times larger arm s separation and 1 times narrower 1 S 3 P 1 transition. The schematic diagram of Mg lower levels is shown in Fig. 2. We want to emphasize the following advantages of Mg 24 atoms for atom interferometry. With Mg atoms macroscopic arm s separation up to.18 mm is possible. Due to the absence of Mg 24,26 ground state hyperfine structure the 1 S 1 P 1 transition is ideal for laser cooling. Very narrow natural line width (γ/2π 3 Hz) of the 1 S 3 P 1 intercombination transition makes this system promising for a frequency standard in blue spectral range. To realize all potential possibility of the Mg interferometer one have to reach extremely high resolution at 457 nm up to 1 Hz and to cool down an atomic beam to the velocities in the range of tens m/s. For Mg interferometer with a few meters dimension of an atomic beam machine the response factors (interference patterns shift in rad.) of the inertial sensor based on it will 1 P 1 τ = 2.2 ns λ = nm 2 τ = 5 ms GHz P,1,2 be s/rad for rotation and 1 4 s 2 /m for acceleration measurements. It is possible to build up the frequency standard base on this interferometer with a relative frequency discriminator width equal to and to obtain a long term frequency stability equal to Δν/ν / S. 1. LASER SYSTEMS To carry out atom interferometry experiments with Mg one has to develop two laser systems. The first one at the wavelength λ = 457 nm we need for atomic wave splitter and recombiner and the second system at 285 nm, for laser cooling of Mg beam. The following parameters of the system at 457 nm are needed to realize completely the possibility of the Mg interferometer: linewidth of the system Δν < 3 Hz; output power P 457 > 5 mw. High power request is due to the value of saturation power for 1 S 3 P 1 transition, P s = hω 3 /(12πτc 2 )π(2.4uτ) 2 /2 = 52 mw, where h is Plank constant, ω/2π is the frequency of the transition, τ is the upper state life time equal to 5.1 ms, u is mean thermal velocity of Mg atom, u = 73 m/s, and c is light velocity. It is possible to build up this system using cw dye laser with UV Ar ++ -laser pumping. This way was realized in [7]. We have developed the laser source based on Ti:Sap laser at 914 nm with SHG in nonlinear crystals. From our point of view this way is more suitable. Short term frequency stability of a Ti:Sap laser is better than that of a dye laser and it is easily to reach narrow laser linewidth. With recently developed Nd:YVO 4 /LBO high power lasers for Ti:Sap pumping this machine may be all solid state and highly flexible system which gives the possibility to obtain high quality cw radiation in the NIR range ( μm) and in the range of μm with SHG in nonlinear crystals. Figure 3 shows our laser system at 457 nm. The output power of our home-made ring Ti:Sap laser reaches 1 W at 914 nm with all lines 18 W Ar + -laser pumping. Pound side band technique is used to lock the frequency of the laser to high stable Fabry Perot interferometer (FSR = 3 MHz, F = 3). The estimated linewidth of the 1 S λ = nm Fig. 2. Atomic level scheme of Mg.

3 118 BAGAYEV et al. Ar-laser 18 W Lock sys. F P λ/4 Thermo-stab. sys. Ti:Sap. laser λ = 914 nm 1W PhD DBM EOM 6 MHz AOM ~ λ/4 Ω = 8 ± 5 MHz λ/4 λ/2 M1 M3 LBO + M4 M2 f = 1 cm pzt f = 17 cm PhD _ 457 nm 2 mw Fig. 3. Laser system at 457 nm. laser is ~1 khz which is limited by stability of our Fabry Perot interferometer. We use enhanced cavity SHG in 1 mm long LBO crystal to obtain 2 mw radiation at 457 nm with the linewidth equal to ~2 khz. Recently we developed noncritical phase matching SHG with KNbO 3 nonlinear crystal. More than 2 mw at 457 nm have been obtained with 6 mw power at 914 nm. The long term frequency stability of 457 nm laser system is very important to carry out the experiments with Mg at a few tens Hz level of resolution. Our first experiments with developed 457 nm laser system were dealing with the test of possibility to use saturation resonances in external magnesium cell for long term frequency stabilization. The original construction of external Mg cell has been developed for these experiments. Figure 4 shows our Mg cell. By tuning the temperature of cell finger with Mg from 38 to 46 C it was possible to change Mg vapor pressure in the range of 1 3 mtorr and to obtain optical density of the cell Pump MgF 2 windows 19 cm P Mg = 1 2 torr Cooling Silica window Heating Stainless steel tube Temperature control t = 45 C Fig. 4. Magnesium absorption cell. equal to αl ~ 1. Figure 5 shows the saturation resonance at 457 nm we have observed for the first time in the external absorption cell. From these experiments pressure broadening ΔΓ/ΔP Mg = 12.5 ± 1.5 khz/mtorr of the resonances was measured. The contrast of the resonances was only.5% due to low value of saturation parameter S The estimated long term frequency stability have to be Δν/ν (τ = 1s). Nevertheless, with 1 mw saturated beam power the long term frequency stability Δν/ν 1 14 (τ = 1 1 s) will be possible. For laser cooling of Mg beam we developed the laser source based on home-made, single mode R6G dye laser (λ = 57 nm) with enhanced cavity SHG in BBO crystal. The request to frequency stability of this source isn t so strong as for radiation at 457 nm. The natural width of the 1 S 1 P 1 transition is equal to ~8 MHz and it is enough to have the linewidth at the level of a few hundred of khz. However, the request to the power of the radiation at 285 nm is strong due to the high saturation intensity of 1 S 1 P 1 transition equal to I s.5 W/cm 2. The output power at the level of 5 mw will be sufficient for laser cooling. Figure 6 shows the schematic diagram of our 285 nm laser system. We locked the frequency of the dye laser to high stable Fabry Perot interferometer (FSR = 3 MHz, F ~ 5) using Pound sideband technique as in the case of our Ti:Sap laser. High modulation frequency (2 MHz) was used in this scheme which has advantage in stable long time operation of the lock system. The frequency jitter of a few hundred khz is limited by the operation band of the frequency lock system. The 5 khz band of the servo loop is limited by the response time of the piezoceramic (pzt) we used for laser frequency correction. The enhanced cavity SHG in 1 mm long BBO crystal results in up to 7 mw output power at 285 nm with 1 W output power of the dye laser. We used the same

4 ATOM INTERFEROMETRY WITH Mg BEAMS 1181 Signal, arb. units Detuning, MHz Fig. 5. Saturation resonance at 457 nm (first derivative signal) with Γ = 25 khz (HWHM): Mg pressure in the cell is 1 mtorr, laser beam waist is w = 1 mm, power of the saturated beam is P sat = 5 mw, laser frequency deviation A = 19 khz ( f mod = 182 Hz), lock-in-amplifier time constant is τ = 3 ms. Mg to obtain torr vapor pressure. The scheme of the setup for frequency stabilization of the UV laser system to the 1 S 1 P 1 magnesium transition is shown at Fig. 7. With two magnetic coils it was possible to create rather uniform longitudinal magnetic field up to 3 G inside the absorption cell. To obtain an error signal for the stabilization system we modulated magnetic field. The frequency of σ +/ -component of the 1 S 1 P 1 transition was also modulated due to Zeeman effect. Figure 8 shows the saturation resonances in the external absorption cell at 285 nm. The first harmonic signal at Fig. 8 strongly differ from a dispersion-like shape. This is the sign of an atomic velocity distribution distortion due to interaction with resonant laser field. This phenomenon is important in the case of a strong closed transition and low pressure gas [8, 9]. Second harmonic signal shows dispersion-like shape and it was used for frequency stabilization. Tuning the dc magnetic field inside the cell it was possible to tune locked laser frequency in the range of ±4 MHz (±5 Γ) near the center of the 1 S 1 P 1 transition. Pound sideband technique to tune the enhanced cavity with nonlinear crystal to resonance with the frequency of radiation at 57 nm. To carry out laser cooling of Mg beam it is very important to lock the frequency of our UV laser source to the frequency of the 1 S 1 P 1 transition. We used saturation resonances in the external absorption cell to lock the laser frequency to Mg fast transition. In the case of the strong 1 S 1 P 1 transition 1 cm long cell with Mg pressure only torr was sufficient to reach the optical density of the cell equal to αl ~ 1 and to obtain high contrast saturation resonances. The 1 cm long glass cell with the walls at room temperature was used as Mg absorption cell. Inside the cell we heat up the small oven with a metallic 2. ATOM INTERFEROMETRY EXPERIMENTS WITH THERMAL Mg BEAM The Mg beam machine was developed to carry out atom interferometry and high resolution spectroscopy experiments. Figure 9 shows the schematic diagram of our Mg beam setup. The thermal Mg beam is formed by.8 mm hole in the oven and by the set of diaphragms inside the vacuum chamber. Mg vapor pressure inside the oven is controlled by the temperature stabilization system. The vacuum chamber is pumped by the diffusion (64 l/s) and the ion (25 l/s) pumps. The additional liquid nitrogen trap was constructed to reduce the pressure of scattered Mg atoms and residual background gas. Usually the residual gas pressure was less than 1 6 torr. The beam machine has two interaction 18 MHz ~ Ar + -laser 15 W Lock sys. Dye laser λ = 57 nm 1 W DBM 2 MHz ~ DKDP EOM PhD PhD BBO Lock Sys. To pzt F P λ/4 TaLiO 3 EOM f = 8 mm pzt Thermo-stab. sys. Up to 7 mw, λ = 285 nm Fig. 6. Laser system at 285 nm.

5 1182 BAGAYEV et al. Dye laser 57 nm P = 1 W BBO cavity 285 nm up to 7 mw Mg cell λ/4 Lock F-P Amp. + _ AT PD Lock sys. Lock-in amp. To beam experiment ~ 18 Hz 36 Hz Fig. 7. Frequency lock scheme of the laser system at 285 nm. chambers with 5 cm optical high quality windows. The result of interaction between laser and atomic beams can be detected by the photomultipliers located near interaction zones and at the end face of the beam machine 1 m downstream the interaction zone. Two cats eye retroreflectors give us the possibility to install the geometry of 4 separated laser fields. The density of the Mg beam in the interaction zone was 1 8 cm 3 and the flux of magnesium atoms interacted with the laser beams was about 1 12 atoms/s. Two counterpropagating pairs of the laser beams (Borde geometry, see Fig. 1) interact with the Mg beam. The distance between the beams in pair was equal to d = 3 mm and Signal, arb. units Detuning, MHz Fig. 8. Saturation absorption resonances at 285 nm (first derivative signal) for three Mg isotopes Mg 24, Mg 25, Mg 26. the distance between two pairs was L ~ 3 mm. The power of the laser beams (2w = 1 mm) was 5 mw. We modulate the frequency of the laser at 18 Hz with 3 khz modulation amplitude and detect the fluorescence light by the photomultiplier. The fist derivative signal was recorded as a function of the laser frequency detuning. Figure 1 shows the result of our experiment. The fine structure in the center of observed line disappears when we stop two beams (one from each pair) and only two counterpropagating beams rest. So, the fine structure may be interpreted as a result of an atom interference. Because of the short coherence length of atomic waves in the thermal atomic beam only the zero order interference fringes were detected. Two sharp picks in the center of the line are the recoil doublet. The solid curve at Fig. 1 is the calculated line shape. The recoil doublet with frequency distance between two components equal to 2δ = k 2 /m 2π 8 khz was resolved in this experiment. This experiment also demonstrated the resolution of our laser spectrometer at 457 nm better than 3 khz limited by the stability of the reference cavity we used for laser frequency stabilization. To increase the resolution of the laser spectrometer at 457 nm we recently developed the new high stable Fabry Perot interferometer with UHR mirrors optically contacted to 4 cm long and 1 cm in diameter Zerodur spacer. We expect the linewidth of our 457 nm system less than 1 khz with this high-finesse (F 4) interferometer and with much broader band of the new servo loop based on the intracavity EOM. But to observe an interference fringes with the width <1 khz one have to cool down Mg beam because of in the case of thermal Mg beam it will be very difficult experimentally realize the laser beams separation d > 1 cm.

6 ATOM INTERFEROMETRY WITH Mg BEAMS nm laser sys. PC Thermo control sys. T = 51 C L L = 1 cm Mg Heating sys. d PM Nitrogen trap Diffusion pump f = 3 cm Cats eye Pump Fig. 9. Schematic diagram of the Mg beam machine. 3. LASER COOLING EXPERIMENTS WITH Mg BEAM An atomic beam can be cooled down by means of the interaction with a resonant counterpropagating laser beam [1 12]. This process may be very efficient if a laser beam is resonant to a strong closed transition. Thermal Mg beam can slowed down at interaction distance of few cm if 285 nm laser beam resonant to the 1 S 1 P 1 transition is used for cooling. The Zeeman shift of the magnetic sublevels in an inhomogeneous magnetic field can be used to keep the atom in resonance with the laser frequency and to compensate the Doppler shift which varies during the deceleration [13, 14]. With this technique Ca and Mg atomic beams were cooled down [15 17]. The magnetic field along the deceleration trajectory (z) have to be of the form: B(z) = Δν/μ + kv /μ(1 z/l m ).5, where Δν = (ω L ω )/2π is the laser detuning from the atom transition, μ = 1.4 MHz/G for Mg 1 S 1 P 1 transition, k is light wave number, v is the maximum atom velocity one want to decelerate, L m is the length of the magnet. If also the magnetic field gradient will satisfy the condition db(z)/dz Fk/(2πμm) = (db/dz) max, where F = k/2τ S/(1 + S) is a deceleration force (S is the saturation parameter, S = I/I sat, for Mg 3 I sat = ω /12πτc 2.5 W/cm 2, lifetime of 1 P 1 state τ = 2.2 ns), than atoms with velocities v < v will be slowed down to velocities near zero m/s. The minimal width of the longitudinal velocity distribution of cooled Mg beam limited by the diffusion process due to randomicity of the deceleration force is δv ( /τm) 1/2 1 m/s [18, 19]. The transverse velocity distribution width can be estimated as Δv N 1/2 v rec 1 m/s, where N 3 is the number of absorption/emission cycles needed to stop thermal atoms, v rec = k/m = 5.6 cm/s is Signal, arb. units Detuning, khz Fig. 1. Atom interference with thermal Mg beam (first derivative signal). The solid curve without noise is the calculated line shape. Lock-in-amplifier time constant is τ = 3 s.

7 1184 BAGAYEV et al. Mg v M M 1 ( ) Nd 15 Fe 77 B 8 permanent magnets Magnetic core 1 cm Magnetic field, G 3 2 z B(z) (b) Δ = μb ω laser Fig. 11. (a) Schematic view of the cooling magnet and the transverse field geometry. The shape of the magnetic cores with thickness 1 mm (perpendicular to the plan of the figure) was designed to obtain proper geometry of the magnetic field. By changing the angle and the distance between cores it was possible to change the geometry of the magnetic field. (b) The magnetic field inside the magnetic cores gap: the curve with circles is the calculated magnetic field with Δν = 4 MHz, L m = 1.3 cm, v = 1 m/s, the curve with squares is the experimental one. σ _ Δ B out ω z, mm σ + ω Mg recoil velocity. Without transverse cooling of the beam it is difficult to obtain Mg beam with the width of longitudinal velocity distribution less than 1 2 m/s. Usually the width of distribution is limited by so called Doppler limit, Δv = γ/k = 1/τk 22.4 m/s for Mg atoms. Another rather serious problem is the difficulties to extract a cooled atomic beam from a magnet due to so called postcooling of atoms. In spite of the frequency detuning of several γ cooled atoms still continue to interact with a laser beam in the space after a magnet and will be stopped or even be accelerated back. In the case of the magnesium, atoms with the velocities of 2 m/s will be stopped at the distance of few millimeters even the detuning will be ~5γ 2π 4 MHz. The most promising choice to extract cooled atoms is to deflect them just at the end of the magnet by means of the additional laser beam with the k vector almost perpendicular to cooled atomic beam [2, 21] or by means of one-dimensional optical molasses [15]. In our first Mg beam cooling experiments the magnetic field geometry was adapted to extract relatively fast beam with the velocities about 1 2 m/s. Usually, the geometry of a longitudinal magnetic field and a circular polarized laser beam used for Zeeman cooling. We proposed the cooling scheme with a transverse magnetic field and plane polarized laser beam (E B k). In this case the intensity of σ Zeeman component used for cooling is two times less than in the case of the usual scheme. This is disadvantage of our scheme. But our scheme is much more flexible to create the proper geometry of a magnetic field especially in the case of a short deceleration length when a permanent magnets can be used. Figure 11 shows the scheme of our cooling magnet and the geometry of magnetic field. The magnet was optimized for laser detuning of Δν = 4 MHz. Cooling beam P = 2 mw Deflection beam P = 2 mw E Analyzer beam P =.1 mw M Therm. Mg beam B 1 cm B a Fiber Cooled Mg beam Velocity Zeeman analyzer PM Ampl. PC Fig. 12. Schematic view of the experimental setup for laser cooling and deflection of Mg beam.

8 ATOM INTERFEROMETRY WITH Mg BEAMS 1185 Positive detuning is preferable to extract atoms with velocities v γ/k. The value of Δν 4 MHz was chosen due to the two reasons. The possibility of our laser system to be controllably detuned from the center of the transition was limited by the value of ±4 MHz. To deflect the cooled atoms the frequency of the laser beam has to be near ω. In our case the deflection beam was produced from the same laser system with the acousto-optic modulator (AOM). The frequency shift of our AOM was limited by the value of 4 MHz in the two-pass geometry. The magnetic field gradient larger than (db/dz) max at point B out (see Fig. 11b) was created to extract the atoms with the velocities v out = λ(μb out Δν) 16 m/s. The schematic view of our setup for laser cooling is shown at Fig. 12. The Mg beam diameter in the interaction zone was ~1 mm. The cooling beam (ω = ω + 2π 4 MHz) with the waist of w 1 mm and the power of P 2 mw was slightly focused to the Mg oven aperture. The deflection beam (ω = ω ) with w 1 mm and power P 2 mw crossed the atomic beam almost perpendicular. It was possible to deflect the cooled Mg beam by an angle of ~5 and to direct it to our velocity analyzer just near the edge of the mirror M. The distance between the end of the magnet and the velocity analyzer was ~5 cm. Usually, to study a velocity distribution an additional laser system is used. By tuning the frequency of the laser beam crossed an atomic beam at the angle θ 9 and by recording the fluorescence of the atomic beam versus laser detuning it is possible to reconstruct the velocity distribution. We proposed another scheme which give possibility to study velocity distribution without an additional tunable laser system. Instead of a laser frequency tuning a frequency of the σ Zeeman component of the transition can be tuned in a magnetic field. In our case, the frequency of low power (P ~.1 mw, w ~ 1 mm) analyzer beam was fixed at ω. The magnetic field between the poles of the C-electromagnet was tuned with winding current. The analyzer beam (E B k) interact with the counterpropagating atomic beam in the volume with rather uniform magnetic field between the electromagnet poles. The fluorescence light was collected and directed to photo-multiplier by 3 μm silica fiber. The signal from the photo-multiplier was recorded versus the magnetic field. With this signal the velocity distribution of Mg beam can be easily reconstructed. Figure 13 shows the velocity distribution of cooled and deflected Mg beam measured by our Zeeman velocity analyzer. To measure the velocity distribution of thermal Mg beam the cooling and deflecting laser beams were stopped. With our Mg beam setup it was possible to turn under control the axis of the Mg beam to direct it to the analyzer. Our first laser cooling experiment shows that sufficient part of atoms from thermal beam was cooled down and deflected. The mean velocity of cooled beam was v ~ 2 m/s, as it was expected, with the width (FWHM) of Δv ~ 5 m/s. Further optimization of the parameters of Signal, arb. units Cooled and deflected beam Without cooling Velocity, m/s Fig. 13. Velocity distribution of cooled and deflected Mg beam with respect to thermal Mg beam. cooling and deflection will be performed to obtain Mg beam with the mean velocity of v < 1 m/s and with the distribution width Δv 2 m/s. 4. SUMMARY We have developed the laser systems for Mg interferometry experiments. The laser system at 457 nm was based on cw ring Ti:Sap laser and SHG in the nonlinear crystals. The power of the 457 nm laser source was 2 mw with SHG in the enhanced cavity contained LBO crystal and more than 2 mw with KNbO 3 crystal. The linewidth of the radiation at 457 nm was ~2 khz. With this system the saturation absorption resonances in the external cell at the 1 S 3 P 1 Mg transition were observed for the first time. Pressure broadening of saturation resonances in external cell ΔΓ/ΔP Mg = 12.5 ± 1.5 khz/mtorr was measured. With 1 mw power at 457 nm it will be possible to obtain a long term frequency stability of Δν/ν 1 14 (τ = 1 1 s) using saturation resonances in the external cell. The atom interferometry experiment with thermal Mg beam was performed in the four-beam Borde geometry. The zero order interference fringes correspondent to the recoil doublet were detected with the resolution of ~3 khz. Further improvement of the resolution will be possible with cooled Mg beam. For laser cooling of Mg beam we developed the laser system at 285 nm based on cw ring dye laser and SHG in the enhanced cavity with BBO crystal. The output power up to 7 mw at 285 nm has been obtained. The saturation resonances in the external Mg cell situated in magnetic field were used to lock the frequency of the laser system to Zeeman σ /+ component of the 1 S 1 P 1 transition. By tuning the magnetic field it was possible to tune the frequency of the laser system in the range of ±4 MHz. We pro-

9 1186 BAGAYEV et al. posed and realized Zeeman laser cooling scheme with a transverse magnetic field (E B k). From our point of view this scheme is more flexible to create the proper geometry of the magnetic field especially in the case of a short deceleration length when permanent magnets can be used. The velocity analyzer based on Zeeman effect was developed to study Mg beam velocity distribution. With this analyzer it is possible to study beam velocity distribution without an additional tunable laser system. The deflection of the Mg beam was used to extract cooled Mg beam from the cooling magnet. With the laser beam crossed atomic beam almost perpendicular the deflection angle of cooled Mg atoms was ~5. The Mg atomic beam with the mean velocity of ~2 m/s and the width of velocity distribution of ~5 m/s (FWHM) was produced. This Mg beam with the flux of ~1 11 atoms/s will be used in atom interferometry and high-resolution spectroscopy experiments with the resolution better than 1 khz. This work was supported by Russian Foundation for Basic Research, grants and REFERENCES , Atom Interferometry, Berman, P.R., Ed. (San Diego: Academic). 2. Baklanov, Ye.V., Dubetsky, B., and Chebotayev, V.P., 1976, Appl. Phys., 9, Dubetsky, B. et al., 1984, Pis ma Zh. Eksp. Teor. Fiz., 39, Borde, Ch.J., 1989, Phys. Lett. A, 14, Strumia, F., 1972, Metrologia, 8, Riehle et al., 1991, Phys. Rev. Lett., 67, Sterr, U. et al., 1992, Appl. Phys. B, 54, Kazantsev, A.P., Surdutovich, G.I., and Yakovlev, V.P., 1986, JETP Lett., 43, no. 5, Grimm, R. and Mlynek, J., 1989, Appl. Phys. B, 49, Hansch, T. and Sawlow, A., 1975, Opt. Commun., 13, Wineland, D. and Dehmelt, H., 1975, Bull. Am. Phys. Soc., 2, Andreev, S.V., Balykin, V.I., Letokhov, V.S., and Minogin, V.G., 1981, JETP Lett., 34, Phillips, W.D. and Metcalf, H., 1982, Phys. Rev. Lett., 48, Prodan, J.V., Phillips, W.D., and Metcalf, H., 1982, Phys. Rev. Lett., 49, Witte, A., Kisters, T., Riehle, F., and Helmcke, J., 1992, J. Opt. Soc. Am. B, 9, Beverini, N., Giammanco, F., Maccioni, E., et al., 1989, J. Opt. Soc. Am. B, 6, Sengstock, K., Sterr, U., Bettermann, D., et al., 1993, in Optics III, Ehlotzky, Ed. (Berlin: Springer), p Krasnov, I.V. and Shaparev, N.Ya., 1979, Zh. Eksp. Teor. Fiz., 77, Minogin, V.G., 198, Opt. Commun., 34, Ashkin, A., 197, Phys. Rev. Lett., 25, Nellessen, J., Sengstock, K., Muller, J.H., and Ertmer, W., 1989, Europhys. Lett., 9 (2), 133.