Samir Bali - Academia.edu (original) (raw)

Papers by Samir Bali

We report measurements of the intensity correlations of scattered light from atoms in optical mol... more We report measurements of the intensity correlations of scattered light from atoms in optical molasses. For small numbers of atoms, the observations are consistent with recent models of the Rayleigh and Raman contributions to the frequency spectrum. Magnetic fields on the order of 100 mG significantly broaden the spectrum. Radiation trapping results in reduction of the size of the correlations as well as broadening of the spectrum.

Optics Letters, Oct 1, 1999

We demonstrate a two-window heterodyne method for measuring the x p cross correlation, ͗E ‫ء‬ ͑x͒... more We demonstrate a two-window heterodyne method for measuring the x p cross correlation, ͗E ‫ء‬ ͑x͒E ͑ p͒͘, of an optical f ield E for transverse position x and transverse momentum p. This scheme permits independent control of the x and p resolution. A simple linear transform of the x p correlation function yields the Wigner phase-space distribution. This technique is useful for both coherent and low-coherence light sources and may permit new biological imaging techniques based on transverse coherence measurement with time gating. We point out an interesting analogy between x p correlation measurements for classical-wave and quantum f ields. 

Aps Division of Atomic Molecular and Optical Physics Meeting Abstracts, Jun 1, 2000

We present a simple Fokker-Planck model for the evolution of the spatial distribution of atoms in... more We present a simple Fokker-Planck model for the evolution of the spatial distribution of atoms in a CO2 laser trap which is loaded continuously from a magneto-optical trap. We find that deep traps reach equilibrium much more slowly than shallow ones. The number of trapped atoms is found to be strongly dependent on the ratio of the well depth to the temperature of the atoms. A universal function for the equilibrium number of trapped atoms is given.

Optics Communications, Sep 1, 1990

With the help of photon coincidence counting measurements we have studied the dependence of the r... more With the help of photon coincidence counting measurements we have studied the dependence of the relative intensity fluctuations λ(0)=<(Δ I) 2>/< I> 2 on the output light intensity < I> of a single-mode dye jet laser at two different dye flow velocities. We find that varying the flow velocity causes a rotation and a thickness change of the dye jet. When these effects are compensated, there is no discernible dependence of the dye laser statistics on the flow velocity in the range 12.1 m/s to 13.4 m/s.

We demonstrate evaporative cooling of ^6Li fermions in an optical trap by utilizing a |3,1> mi... more We demonstrate evaporative cooling of ^6Li fermions in an optical trap by utilizing a |3,1> mixture of hyperfine states(The hyperfine states are labeled |1>-|6> in order of increasing energy in a magnetic field.). During the evaporation, we observe an anomalously large elastic scattering length a_31. Initially, the noninteracting |1,2> combination is loaded from a MOT into a CO2 laser trap which has a 1/e lifetime of 370 sec. Evaporative cooling is initiated by coherently transferring population from state |2> to state |3>, and the number of remaining atoms N(t) is measured as a function of time at fixed well depth. N(t) is compared to predictions based on an s-wave Boltzmann equation with an energy-dependent elastic cross section. The results are consistent with our prediction(We are indebted to F. Abeleen and B. J. Verhaar who rigorously confirmed our approximate calculation of the B-field dependence of a_31) and showed that the inelastic |3,1>-|1,2> dipola...

Ideally, optical traps are well suited for exploring fundamental interactions in an ultracold two... more Ideally, optical traps are well suited for exploring fundamental interactions in an ultracold two-state fermionic gas. Such traps permit storage of multiple spin states, enabling s-wave scattering which is essential for interparticle interactions and evaporative cooling. Unfortunately, optical traps have not been suitable for this purpose, because they suffered from unexplained heating rates which limited the storage time to a few seconds in an ultra high vacuum. Recently, we have developed an ultrastable CO2 laser trap for which the number of trapped atoms decays exponentially with a time constant of 300 sec, comparable to the best reported magnetic traps. The small residual heating rates attained with this system potentially enable efficient evaporative cooling. We have trapped more than 500,000 atoms at an initial temperature of 200 muK, and we will report on our progress toward attaining degeneracy.

We report on the design and construction of tapered amplifier (TA) systems in a primarily undergr... more We report on the design and construction of tapered amplifier (TA) systems in a primarily undergraduate setting, each system costing less than 4000 to build. Plots of power output are presented versus seed power and TA current, including plots of TA output coupled through a single-mode optical fiber. We acknowledge invaluable discussions with Prof. D. Yavuz's group at Univ. of Wisconsin, Madison on the optics for collimation of the seed laser into the TA chip, and of the TA output. Also, we have based our current and temperature drivers for the TA system on circuit designs by Prof. D. Steck's group at the Univ. of Oregon, Eugene.

$Research paper thumbnail of Refractive index sensing of turbid media by differentiation of the reflectance profile: Analysis of error$

Refractive index detection typically consists of a measurement of the reflectance of light from t... more Refractive index detection typically consists of a measurement of the reflectance of light from the sample surface for various angles of incidence, and determining the critical angle for total internal reflection (TIR). A commonly used technique for locating the critical angle is to differentiate the angular reflectance profile with respect to the incidence angle, and look for the point of maximum change of slope. For turbid media this differentiation technique leads to errors in refractive index measurement, which need to be accurately estimated. We show that previous attempts by other workers to calculate the error using traditional Fresnel theory yield an expression that is impossible to physically justify, and hence must be incorrect. We calculate the error using a recent model of TIR in turbid media by Calhoun, et al. (Opt. Lett. 35, 1224 (2010)) which departs from traditional Fresnel theory, and show that this error varies with turbidity in an expected manner. Important differ...

We describe how we have built a Magneto-Optical Trap (MOT) for confining neutral Rubidium atoms. ... more We describe how we have built a Magneto-Optical Trap (MOT) for confining neutral Rubidium atoms. Images of the trapped cloud of atoms will be displayed, and effects of laser detuning and alignment on the trap will be shown. The regime of radiation trapping, where atoms in the cloud exchange photons with each other, will be briefly discussed.

Photon statistics of light fields are analyzed using a two-photon detection scheme. Counting dist... more Photon statistics of light fields are analyzed using a two-photon detection scheme. Counting distributions are obtained for the output of a degenerate parametric oscillator (DPO) in the limit where the counting interval is much shorter than the coherence time of the light field. Results are compared to the usual one-photon detection scheme.

Two-time intensity correlation functions of a semiconductor laser have been measured by using Typ... more Two-time intensity correlation functions of a semiconductor laser have been measured by using Type II second harmonic generation. The fundamental beam is split into two orthogonally polarized beams. Relative delays of upto 40 ns are introduced, and the beams are recombined in a nonlinear crystal. The second harmonic signal is measured as a function of delay for several different operating points of the laser.

Saratov Fall Meeting '99: Optical Technologies in Biophysics and Medicine, 2000

ABSTRACT We explore enhanced backscatter from a random medium using time-resolved optical phase s... more ABSTRACT We explore enhanced backscatter from a random medium using time-resolved optical phase space measurement, i.e. measurement of joint position and momentum (x, p) distributions of the light field as a function of propagation time in the medium. Enhanced backscatter is a coherent effect and is not predicted by radiative transport theories. By using a low-coherence source in a heterodyne detection scheme, we observe enhanced backscattering resolved by path length in the random medium, effectively providing timing resolution. Such time-resolved studies are important for exploring the evolution of optical coherence as a function of penetration depth in the random medium. Optical phase space methods provide a visual as well as quantitative method of characterizing the spatial coherence properties and wavefront curvature of the input and scattered fields. These techniques may provide new venues for using optical coherence in medical imaging.

Quantum Communication, Computing, and Measurement 2, 2002

ABSTRACT We measure squeezing spectra for phase-dependent fluorescence of coherently driven two-l... more ABSTRACT We measure squeezing spectra for phase-dependent fluorescence of coherently driven two-level atoms in free space. The measured spectra are in excellent agreement with our predictions for a single two-level atom. We find that maximum squeezing occurs for homodyne detection at a phase near ±45° relative to the exciting field, rather than in the in- or out-of-phase quadratures. A new physical picture of phase-dependent noise that incorporates quantum collapses into a Bloch vector model shows why this occurs.

$Research paper thumbnail of Sensitive real-time measurement of the refractive index and attenuation coefficient of milk and milk-cream mixtures$

Journal of dairy science, 2010

We demonstrate a first simultaneous measurement of both the refractive index and the attenuation ... more We demonstrate a first simultaneous measurement of both the refractive index and the attenuation coefficient (defined as the sum of the scattering and absorption coefficients) of highly turbid milk and milk-cream mixtures. We achieve this by observing the real-time reflectance profile of a divergent laser beam made incident on the surface of the milk sample. The experiments were carried out on commercial milk samples with fat volume concentrations of 0.5 or less, 1.6, and 3.3%, and on milk-cream mixtures with fat volume concentrations of 10 and 33.3%, without any dilutions of these samples. We find that the reflectance data are well described, for the first time without any empirical fit-parameters, by Fresnel theory that correctly includes the effect of angle-dependent penetration into the turbid medium on the total internally reflected signal. Therefore, our method provides the most accurate determination to date of the refractive index and attenuation coefficient of milk and milk...

Optical Pulse and Beam Propagation II, 2000

Process monitoring is a vital part of industrial laser applications that enables intelligent cont... more Process monitoring is a vital part of industrial laser applications that enables intelligent control of processes by observing acoustic, optical, thermal and other emissions. By monitoring these emission during laser processing, it is possible to ascertain characteristics that help diagnose features of the laser processed material and hence to optimize the technique. An experimental set up of observing plasmas during laser spot welding is described here. A pulsed Nd:YAG laser was used to spot-weld a variety of materials of different thickness, the plasmas generated during welding were monitored by a number of techniques, and the data obtained was used to characterize the welds. In the study photodiodes were set at different angles and observed the intensity and generation of the plasmas during the laser spot-welding process thereby giving a weld 'signature.' A portable spectrometer was used off-axis to obtain spectra of the emissions from the plasmas. Post process analysis w...

American Journal of Physics, 2014

ABSTRACT We present plans for the construction and operation of a tapered optical amplifier (TA) ... more ABSTRACT We present plans for the construction and operation of a tapered optical amplifier (TA) system seeded by a single-mode, frequency-tunable, near-IR external-cavity diode laser. Our plans include machine drawings for the parts, electronic circuit diagrams, and information on prices and vendors. Instructions are provided on how to safely couple light into and out of the TA chip. Practical aspects of handling the chip are discussed as well. Because many cold atom experiments require light beams with Gaussian spatial profiles, measurements of the tapered amplifier light output through a single-mode optical fiber are presented as a function of seed intensity, polarization, and driving current.

Conference on Coherence and Quantum Optics, 2007

ABSTRACT We have observed Electromagnetically Induced Transparency (EIT) in Rubidium vapor using ... more ABSTRACT We have observed Electromagnetically Induced Transparency (EIT) in Rubidium vapor using a single linearly polarized incident laser beam and an external magnetic field. Progress toward a detailed understanding of the observed subnatural resonances is reported.

$Research paper thumbnail of Real-time measurement of the complex refractive index of turbid colloidal suspensions$

We demonstrate the simultaneous measurement of the real and imaginary parts of the refractive ind... more We demonstrate the simultaneous measurement of the real and imaginary parts of the refractive index of turbid colloidal suspensions by measurement of the intensity reflected from the turbid sample of an incident laser beam. The entire reflectance curve for a range of incident angles around the critical angle for total internal reflection is obtained in real time. We find that

Physical Review Letters, 1999

We demonstrate an ultrastable CO2 laser trap that provides tight confinement of neutral atoms wit... more We demonstrate an ultrastable CO2 laser trap that provides tight confinement of neutral atoms with negligible optical scattering and minimal laser noise induced heating. Using this method, fermionic 6 Li atoms are stored in a 0.4 mK deep well with a 1/e trap lifetime of 300 seconds, consistent with a background pressure of 10 −11 Torr. To our knowledge, this is the longest storage time ever achieved with an all-optical trap, comparable to the best reported magnetic traps.