Papers by A. Kumarakrishnan
ABSTRACT
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Atom interferometers (AIs) have been recognized for their potential to make one of the most preci... more Atom interferometers (AIs) have been recognized for their potential to make one of the most precise measurements of the atomic fine structure constant alpha. We describe sensitive measurements of the atomic recoil frequency omegar = (h/2pi)(Delta k)^2/2m_atom (which can be related to alpha) using an AI that measures the momentum transfer Delta k imparted to cold ^85Rb atoms in a single hyperfine ground state. Our measurements have been carried out both in the time domain and in the frequency domain. In the time domain, the excitation scheme is reminiscent of a photon echo experiment. Two off resonant standing wave pulses separated by t = T are used diffract and rephase a superposition of momentum states. This results in an atomic density grating in the vicinity of t = 2i^T, which is detected by measuring the amplitude of coherently back-scattered light from the sample. The amplitude of this echo signal is recorded as a function of T. Since the signal is modulated at omega_r, the pre...
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Physical Review A, 2008
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Physical Review A, 2006
We have observed the effects of magnetic field gradients and gravitational acceleration on gratin... more We have observed the effects of magnetic field gradients and gravitational acceleration on grating echoes in a time domain single state atom interferometer that uses laser cooled Rb atoms. These observations are compared to theoretical predictions based on a simplified model. The oscillatory dependence of the echo amplitude due to the magnetic field gradient is in agreement with the predicted
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Physical Review A, 2008
We have developed a theoretical description of the evolution of ground state coherences between m... more We have developed a theoretical description of the evolution of ground state coherences between magnetic sublevels in Rb vapor in the presence of a magnetic field along an arbitrary direction. This formalism uses a rotation matrix approach to describe the evolution of coherences created by two traveling wave laser pulses with orthogonal polarizations. The effect of a magnetic field can be described as a time dependent rotation of the atomic system about the quantization axis. Predictions based on this approach are shown to agree with experiments. By using rate equations to model atomic coherences, it is also possible to predict the evolution of coherence grating echoes in a magnetic field. Echoes are realized by rephasing the coherences using a second set of traveling wave pulses. The two sets of traveling wave pulses are separated by t = T so that the effect of Doppler dephasing is eliminated at t = 2T resulting in the formation of an echo. Applications relating to precision measurements of atomic g factor ratios are considered.
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We have measured the effects of light scattering and collisions on the signal from a single state... more We have measured the effects of light scattering and collisions on the signal from a single state atom interferometer that uses laser cooled ^85Rb. Two standing wave pulses separated by time T are used to diffract and rephase momentum states (corresponding to the F=3 ground state) in the vicinity of t=2T. Light scattering and collisions reduce the timescale over which matter-wave interference can be observed. The decay rate of the signal is linearly proportional to the intensity of background standing wave light. The decay rate also scales inversely as the square of the detuning of the travelling components of the standing wave with respect to the F=3 ->F=4 transition. These observations are consistent with the scattering rate associated with a standing wave potential. By varying the vapour pressure of the background ^85Rb vapour, we show that the experiment is sensitive to velocity changes of ˜100 mum/s and that the signal decay can be used to measure the cross section for hot-c...
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Canadian Journal of Physics, 2003
We have used an acousto-optic modulator (AOM) to impose a frequency-modulated signal on an incide... more We have used an acousto-optic modulator (AOM) to impose a frequency-modulated signal on an incident laser beam. The incident laser beam is focussed into the AOM where it undergoes Bragg diffraction and is then retro-reflected. The diffracted beam is also retro-reflected so that it is diffracted again by the AOM and overlaps the incident beam. The overlapped beams are frequency shifted with respect to each other. These features allow us to detect the frequency-modulated signal with high signal-to-noise ratio using heterodyne detection. Since the optical setup is simple and can be made very compact, this device may be ideal for certain forms of high-speed, free-space optical communication. We demonstrate a 1 MHz data transmission rate in the Bragg regime. We measured the acceptance angle of the device and find that it is limited only by the divergence of the focussed laser beam and the divergence of the acoustic waves in the AOM crystal. We have also studied the range of acoustic frequencies and drive power of the AOM, for which the retro-reflected beam can be detected with adequate signal to noise.
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Canadian Journal of Physics, 2006
ABSTRACT We discuss design considerations and construction of a home-built electro-optic phase mo... more ABSTRACT We discuss design considerations and construction of a home-built electro-optic phase modulator (EOM) that can be used for locking a laser to an atomic transition. The EOM is designed to operate at a resonant frequency of ≈20 MHz and imposes a phase modulation on a laser beam. The phase-modulated light is sent through a reference cell containing a dilute gas of rubidium atoms. When the laser is scanned over an atomic resonance, the absorption of light through the cell can be detected and mixed down to DC to produce a dispersion shaped “error” signal. The error signal can be used to lock the laser to the atomic resonance. We also describe tests of the basic properties of the resonant circuit. The Q of the circuit is measured to be 10, resulting in 60% efficiency for the first-order sidebands at RF drive powers of 0.7 W. Applications include the spectroscopy of laser-cooled atoms.PACS Nos.: 01.50.Pa, 39.25.+k 32.80.Pj, 42.62.Fi
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Canadian Journal of Physics, 2004
We determine the absolute density of a sample of laser-cooled atoms in a two-level system by reco... more We determine the absolute density of a sample of laser-cooled atoms in a two-level system by recording the absorption spectrum of the Rb-85 5S(1/2) (F = 3, m(f) = 3) --> 5P(3/2) (F' = 4, m'(f) = 4) transition. Trapped atoms were prepared in the (F = 3, m(f) = 3) ground state through optical-pumping techniques. We compare our results with an independent measure of the density that relies on a direct measurement of the number of atoms and size of the atomic sample. We also study the contributions of power broadening, laser line width, and Doppler broadening to the measured absorption spectrum. Our studies suggest that the natural line width (similar to6 MHz) can be measured to a precision of less than similar to50 kHz if the laser line width is measured in real-time with a high-finesse Fabry-Perot cavity.
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The in-situ measurement of the phase space distribution of atoms in a trap is important in the st... more The in-situ measurement of the phase space distribution of atoms in a trap is important in the study of both ordinary and Bose-condensed matter. The current techniques for measuring the density distribution involve imaging the light emitted by atoms in the trap, time-of-flight measurement of the atoms as they fall through a sheet of light(C.D. Wallace, et al, JOSA B,11),703
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Physical Review A, 1998
We have studied superfluorescence (SF) under highly unfavorable conditions of rapid collisional a... more We have studied superfluorescence (SF) under highly unfavorable conditions of rapid collisional and radiative distribution in a Doppler-broadened medium. Nanosecond SF pulses at 5.5 mum were generated on the Ca 4s4p 1P1-3d4s 1D2 transition from a column of calcium vapor buffered with Ar by optically pumping the 4s2 1S0-4s4p 1P1 transition. The Rabi frequency associated with the intense pump pulse prevents the occurrence of SF while the pump laser is on. As a result, the predicted scaling laws that describe the properties of SF in a transversely excited system, such as peak heights, pulse widths, and delay times, are shown to apply in our situation in which the conditions resemble swept excitation. The delay times were found to be in agreement with a fully quantum mechanical calculation which describes the initiation of SF. Measurements of the densities of the three levels, the absolute SF photon yield, and the spatial distribution of the excited states indicate that the system has a quantum yield of unity. The SF intensity increases with an increase in Ar pressure due to collisional redistribution until the collisional dephasing rate inhibits SF. The conditions describing the transition of SF to amplified spontaneous emission allow us to measure the collisional broadening rate for the SF transition.
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Facial Plastic Surgery Clinics of North America, 1997
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Summary form only given. The magnetic grating free induction decay (MGFID) may be produced in a s... more Summary form only given. The magnetic grating free induction decay (MGFID) may be produced in a sample of room temperature (300 K) 35Rb, demonstrating the coherence between alternate magnetic sublevels. The decay rate of this coherence is dominated by the dispersal of the atoms and proportional to the most probable velocity u of the atoms. By slowing and confining the atoms in a magnetooptic trap, the decay rate may be reduced by several orders of magnitude.
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Physical Review A, 1998
We have used two sets of orthogonally polarized traveling-wave pulses separated in time to establ... more We have used two sets of orthogonally polarized traveling-wave pulses separated in time to establish and, subsequently, rephase a spatially periodic coherence grating between the magnetic sublevels of the F=3 ground state in a cloud of laser-cooled 85Rb atoms. The rephasing results in a magnetic grating echo (MGE). We have used the shape of the signals to determine both transverse and longitudinal velocity distributions and to study the effects of magnetic fields. The amplitude of the MGE with counterpropagating pulses is modulated at the atomic recoil frequency, a consequence of matter wave interference.
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Journal of the Optical Society of America B, 2005
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Journal of the Optical Society of America B, 2007
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Journal of the Optical Society of America B, 2005
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We have used an acousto-optic modulator (AOM) to impose an amplitude modulation on an incident La... more We have used an acousto-optic modulator (AOM) to impose an amplitude modulation on an incident Laser beam. The amplitude modulated beam can be sent back through the AOM so that it returns along the direction of the incident beam. However, the return beam is frequency shifted and orthogonally polarized with respect to the incident beam. This feature allows us to detect the amplitude modulated retroreflected signal with high signal to noise using heterodyne detection. Since the setup is very simple and compact, it may be ideally suited for certain forms of high-speed optical communication.
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Canadian Journal of Physics, 2005
ABSTRACT We describe an inexpensive lock-in amplifier that can be built using discrete off-the-sh... more ABSTRACT We describe an inexpensive lock-in amplifier that can be built using discrete off-the-shelf RF components and home-built analog circuits. This lock-in has been used in a feedback loop to lock the frequency of a laser to an atomic transition. The frequency stability was tested by trapping rubidium atoms. The feedback loop involves obtaining a modulated saturated absorption signal from a vapor cell using an acousto-optic modulator to modulate the laser frequency. The absorption signal is sent to the lock-in to generate an error signal, proportional to the first derivative of the absorption, which is fed back to the laser to complete the feedback loop. We also demonstrate a simplified optical setup for viewing the saturated absorption spectrum. In this case, the signal consists of narrow saturated absorption spectra riding on top of a Doppler-broadened pedestal. We show that it is possible to greatly reduce the effect of this background and lock the laser to the atomic resonance by modifying the home-built lock-in to generate an error signal proportional to the third derivative of the absorption. The results of this work can be adapted for advanced undergraduate laboratory work.PACS Nos.: 01.50Pa, 07.50.e, 42.62Fi, 42.60Fc
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Physical Review Letters, 1997
We report the development of an atom interferometer that uses optical standing waves as phase gra... more We report the development of an atom interferometer that uses optical standing waves as phase gratings and operates in the time domain. The observed signal is entirely caused by the wave nature of the atomic center-of-mass motion. The opportunities to measure recoil frequency and gravity acceleration are demonstrated.
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Papers by A. Kumarakrishnan