We propose a new design principle for optimal concentration of light with small diffusivity based on the conservation of local brightness in passive optical transformations. A coordinate transformation is applied on the incoming rays to compensate for the variations in local brightness by the focusing stage. We apply this analytic design for a compact reflective configuration for ideal imaging concentration of diffuse light such as sunlight in one dimension on an elongated target with arbitrary cross-sectional shape at the thermodynamic limit. As illustrations, we present the design for two different target geometries and verify its validity using numerical ray-tracing simulations. The same configuration can be used in reverse as an ideal collimator of a finite diffuse source.
Laser beams can be shaped by controlling either the intensity or phase or coherence distribution separately. With typical laser configurations, the intensity and phase controls are relatively slow and cannot yield high-resolution arbitrarily shaped beams and the coherence control suffers from high power loss. By resorting to a degenerate cavity laser that incorporates an intra-cavity digital spatial light modulator and an intra-cavity spatial Fourier filter, it is possible to exploit a very large number (about 100,000) of independent lasing spatial modes in order to control the properties of the laser output. We have adapted this configuration to develop a novel, rapid and efficient method to generate high resolution laser beams with arbitrary intensity, phase and coherence distributions.
We report the observation of the optomechanical strain applied to thermal and to quantum degenerate $^{87}Rb$ atomic clouds when illuminated by an intense, far detuned homogeneous laser beam. In this regime the atomic cloud acts as a lens which focuses the laser beam. As a back action, the atoms experience a force opposite to the beam deflection, which depends on the atomic cloud density profile. We experimentally demonstrate the basic features of this force, distinguishing it from the well-established scattering and dipole forces. The observed strain saturates, ultimately limiting the momentum impulse that can be transferred to the atoms. This optomechanical force may effectively induce inter-particle interactions, which can be optically tuned.
This paper describes a technique that allows measurement of very small alternating accelerations. It is based on a quantum version of a lock-in amplifier,1 which filters out spectral components far from the frequency of the measured signal, improving the signal-to-noise ratio of the measurement. As a proof-of-principle, a controlled experiment using microwave radiation is performed, modulating the phase of the control pulses at a given frequency. A strong response at twice the modulation frequency is observed as expected. Preliminary results of measurements taken with Raman control are also presented, in which a controlled modulation of the phase was obtained by modulating a piezoelectric actuator, causing one of the Raman mirrors to vibrate.
A signal beam is generated in three and four level-atomic system in hot Rb vapors with N2 buffer in electromagnetically induced transparency (EIT) conditions by adding a pump-beam deflected within a small angle to the coupling and probe beams. Linewidth below 200 Hz and time delay above 1 msec are reported. It is suggested that the generated signal proprieties offer several advantages over the transmitted ones that are used traditionally in EIT applications.
Selections from our recent developments in passive phase locking and coherent combining of lasers are presented. These
include the principles of our approaches, lasers configurations, experimental procedures and results with solid state lasers
and fiber lasers.
KEYWORDS: Resonators, Laser resonators, Gas lasers, Mirrors, Near field, Modes of laser operation, Carbon monoxide, Chemical elements, Laser stabilization, Reflectivity
We demonstrate an approach for stabilizing the transverse mode structure in cases where there is strong coupling between the longitudinal and the transverse modes. In this approach, an intracavity phase element that discriminates and selects a specific transverse mode is inserted into the laser resonator. We show that the discrimination can be so strong that the selection of the single transverse mode remains stable despite changes of the resonator length. We calculated the ratio of the small-signal gain and the gain threshold value for the fundamental and (1,0) Hermite-Gaussian modes, as function of a tiny change &Dgr;z of the resonator length, with and without the phase element. Without the phase element, the tiny change of the axial coordinate z of one of the mirrors of CO2 laser leads to periodical change of different transverse modes. Introducing intracavity phase element preserves a single transverse mode, which is kept practically unchanged with the change of the axial coordinate z, except for a slight periodical change of the output power and the beam quality, due to the periodicity of the resonance conditions.
Dark optical traps use repulsive light forces to confine atoms mostly in the dark where their interaction with the trapping light is largely reduced, to enable long coherence times of the trapped atoms combined with tight confinement. We report on single-beam dark optical traps for ultra-cold atoms. These traps were used to demonstrate new spectroscopic and dynamical effects of the trapped atoms, including the observation of regular and chaotic motion in so called optical "billiards."
A simple method for obtaining a nearly Gaussian laser beam from a high order Hermite-Gaussian mode is presented. The method is based on separating the equal lobes of the high order mode and combining them together coherently. The method was experimentally verified with an arrangement of three mirrors, a 50% beam splitter and a phase tuning plate. The beam quality factor calculated in x-direction for the resulting output beam is 1.045, being very close to that of ideal Gaussian beam. The calculated power leakage is only 1.5%. The experimental near-field and far-field intensity distributions of the output beam have nearly Gaussian cross sections in both the x and y directions, with M2x=1.34 and M2y=1.32. With some modifications, it is possible to obtain an output beam with M2x=1.15 and no power leakage.
A new type of optical instrument, the curved hologram, is introduced that allows us the unique opportunity to independently control its spatial phase function and its shape. We show how proper design of the hologram shape (using a simple analytic procedure) yields perfect uniform collimation, and also collimation and concentration of diffuse (monochromatic) light at the thermodynamic limit of brightness conservation.
A novel single multifunctional holographic optical element is incorporated into a surface measurement system. As a result the system is lightweight, compact, and simpler than conventional ones. Numerical calculation reveals that submicron resolutions are possible both in the horizontal and vertical directions. Finally, experimental results demonstrate the feasibility of the approach.
We present a novel non-contact holographic optical profilometer, which is light weight, compact and relatively
simpler. Computer simulation results reveal that surface measurements with sub-micron resolution are possible both
in the horizontal and vertical directions.
We present a novel aspheric holographic optical element (hOE), having an extended depth of focus while
keeping high lateral resolution. The phase function of the HOE is derived, and computer simulations verify the
theoretical prediction for the optical performances.
Noveldesigns for forming space variant holographic ifiters that perform general types ofcoordinate transformations on two dimensional pictures are presented. The designs are without any paraxial approximations and include planar and curved filter configurations. The experimental results indicate that high quality transformations can be obtained. 1.
Recent advances in the design and recording of holographic optical elements are illustrated by means of two representative examples - focussing lens and multiple beam grating. The focussing lens design method is based on an analytic ray-tracing procedure that yields an analytic solution for the diffractive grating function. It will be elucidated by describing the recording and testing ofaspheric low 1 number focussing elements for 10. 6 microns wavelength having diffraction - limited performance over a broad range of incidence angles. The design of the multiple beam grating is based on solving a set of nonlinear equations to obtain a grating structure that can convert one incident beam into a set of specified output beams. Both the lens and the multiple grating elements are recorded with binary optics that involve computer generated plots with high resolution laser printer and plotolithographic techniques. Reflective and trismissive elements are formed by either etching reflective metal layers or GaAs substrates. 1.
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