Surjya Ram | Homi Bhabha National Institute (HBNI, BARC, MUMBAI) (original) (raw)

Papers by Surjya Ram

$Research paper thumbnail of A toroidal trap for cold <math xmlns="http://www.w3.org/1998/Math/MathML"><semantics><mrow><msup><mrow></mrow><mn>87</mn></msup><mrow><mi>R</mi><mi>b</mi></mrow></mrow><annotation encoding="application/x-tex">{}^{87}{Rb}</annotation></semantics></math>87Rb atoms using an rf-dressed quadrupole trap$

Journal of Physics B: Atomic, Molecular and Optical Physics

We demonstrate the trapping of cold 87 Rb atoms in a toroidal geometry using a rf-dressed quadrup... more We demonstrate the trapping of cold 87 Rb atoms in a toroidal geometry using a rf-dressed quadrupole magnetic trap formed by superposing a strong radio frequency (rf) field on a quadrupole trap. This rf-dressed quadrupole trap has minimum of the potential away from the quadrupole trap centre on a circular path which facilitates the trapping in the toroidal geometry. In the experiments, the laser cooled atoms were first trapped in the quadrupole trap, then cooled evaporatively using a weak rf-field, and finally trapped in the rf-dressed quadrupole trap. The radius of the toroid could be varied by varying the frequency of the dressing rf-field. It has also been demonstrated that a single rf source and an antenna can be used for the rf-evaporative cooling as well as for rf-dressing of atoms. The atoms trapped in the toroidal trap may have applications in realization of an atom gyroscope as well as in studying the quantum gases in low dimensions.

Optical Engineering, 2015

Journal of the Korean Physical Society, 2014

We present studies on the modifications in temperature, number density and phase-space density wh... more We present studies on the modifications in temperature, number density and phase-space density when a laser cooled atom cloud from the optical molasses is trapped in a quadrupole magnetic trap. Theoretically it is shown that for a given temperature and size of the cloud from the molasses, the phase-space density in the magnetic trap first increases with magnetic field gradient and then decreases with it, after attaining a maximum value at an optimum value of magnetic field gradient. The experimentally measured variation in phase-space density in the magnetic trap with the magnetic field gradient has shown the similar trend. However, the experimentally measured values of number density and phase-space density are much lower than their theoretically predicted values. This is attributed to the higher experimentally observed temperature in the magnetic trap than the theoretically predicted temperature. Nevertheless, these studies can be useful to set a higher phase-space density in the trap by setting the optimum value of field gradient of the quadrupole magnetic trap.

Review of Scientific Instruments, 2011

We present our results on transfer of cold (87)Rb atoms from a vapor cell magneto-optical trap to... more We present our results on transfer of cold (87)Rb atoms from a vapor cell magneto-optical trap to ultrahigh vacuum magneto-optical trap (UHV-MOT) using a red-detuned continuous wave push beam in a double-magneto-optical trap setup. We find that use of retro-reflected red-detuned push laser beam results in higher number in UHV-MOT than the number obtained without retro-reflection of push beam.

Review of Scientific Instruments, 2013

We have studied the dependence of atom transfer between two magneto-optical traps (MOTs) on the s... more We have studied the dependence of atom transfer between two magneto-optical traps (MOTs) on the spot-size of a push laser beam in a double magneto-optical trap setup. It was observed that the spot-size of the push beam at vapor-chamber MOT (VC-MOT) affects significantly the transfer of atoms from the VC-MOT to an ultrahigh vacuum MOT (UHV-MOT). The number of atoms accumulated in the UHV-MOT first increases with the push beam spot-size and then decreases with it after attaining a maximum value, for a given power of the push beam. Our results show that the number of atoms accumulated in the UHV-MOT is dependent on the push beam spot-size, push beam power, and capture speed of the UHV-MOT.

Pramana, 2014

ABSTRACT We present here our experimental results on transfer of laser-cooled atom cloud to a qua... more ABSTRACT We present here our experimental results on transfer of laser-cooled atom cloud to a quadrupole magnetic trap. We show that by choosing appropriately the ratio of potential energy in magnetic trap to kinetic energy of cloud in molasses, we can obtain the maximum phase-space density in the magnetic trap. These results guide us to choose the value of current to be switched in the quadrupole coils used for magnetic trapping for a given temperature of the cloud after molasses. This study is also useful to set the initial phase-space density of the cloud before evaporative cooling.

Optical Engineering, 2011

We demonstrate the generation of a collimated hollow beam of variable diameter using a pair of co... more We demonstrate the generation of a collimated hollow beam of variable diameter using a pair of convex and concave metal axicon mirrors. Using these homemade inexpensive convex and concave metal axicon mirrors of equal cone angle, we have generated a good quality hollow beam with high conversion efficiency (~76%) from a Gaussian input beam. The focusing of the generated collimated

Journal of the Korean Physical Society, 2010

ABSTRACT We present the experimental results for a comparison between pulsed and continuous trans... more ABSTRACT We present the experimental results for a comparison between pulsed and continuous transfer of cold 87 Rh atoms between a vapor chamber magneto-optical trap (VC-MOT) and an ultra-high-vacuum magneto-optical trap (UHV-MOT) when using a resonant push beam. We find that employing repetitive cycles of a pulsed and unfocused push beam on an unsaturated VC-MOT cloud results in a significantly higher number of atoms transferred to the UHV-MOT than the number obtained with a continuous push beam focused on a continuous VC-MOT. In pulsed transfer, we find that both the VC-MOT loading duration and the push beam duration play important roles in the transfer process and govern the number of atoms transferred to the UHV-MOT. The parameters and processes affecting the transfer have been investigated and are discussed.

Applied Optics, 2012

We report the generation of a zero-order Bessel beam of continuously variable spot size using a s... more We report the generation of a zero-order Bessel beam of continuously variable spot size using a simple optical setup. We have used a pair of metal axicon mirrors to generate a hollow beam of variable dark diameter. This beam was subsequently focused by a convex lens to get a Bessel beam of variable spot size. We also studied the effect of a hollow-beam ring width on nondiffracting propagation range of the generated beam.

Arxiv preprint arXiv: …, 2010

In our double magneto-optical trap (MOT) setup containing a vapor chamber MOT (VC-MOT) and an ult... more In our double magneto-optical trap (MOT) setup containing a vapor chamber MOT (VC-MOT) and an ultra high vacuum MOT (UHV-MOT) for 87 Rb atoms, we find that transfer of atoms from VC-MOT to UHV-MOT can be enhanced by employing a pulsed VC-MOT loading followed by a pulsed push beam, as compared to that obtained by focusing a continuous wave (CW) push beam on a continuously loaded VC-MOT. By choosing appropriately the VC-MOT duration and push beam duration, the number of atoms in UHV-MOT was ∼3-times the number obtained with a continuous VC-MOT and a CW push beam of optimized power. The processes affecting the pulsed transfer have been studied.