Strong Pump Laser Beam Research Articles

Two-way single-photon-level frequency conversion between 852 nm and 1560 nm for connecting cesium D2 line with the telecom C-band.

A compact setup for two-way single-photon-level frequency conversion between 852 nm and 1560 nm has been implemented with the same periodically-poled magnesium-oxide-doped lithium niobate (PPMgO:LN) bulk crystals for connecting cesium D2 line (852 nm) to telecom C-band. By single-pass mixing a strong continuous-wave pump laser at 1878 nm and the single-photon-level periodical signal pulses in a 50-mm-long PPMgO:LN bulk crystal, the conversion efficiency of ∼ 1.7% (∼ 1.9%) for 852-nm to 1560-nm down-conversion (1560-nm to 852-nm up-conversion) have been achieved. We analyzed noise photons induced by the strong pump laser beam, including the spontaneous Raman scattering (SRS) and the spontaneous parametric down-conversion (SPDC) photons, and the photons generated in the cascaded nonlinear processes. The signal-to-noise ratio (SNR) has been improved remarkably by using the narrow-band filters and changing polarization of the noise photons in the difference frequency generation (DFG) process. With further improvement of the conversion efficiency by employing PPMgO:LN waveguide, instead of bulk crystal, our study may provide the basics for cyclic photon conversion in quantum network.

Spatial phase modulation and all-optical switching of tris(2`,2-bipyridyl)iron(II) tetrafluoroborate

The spatial self-phase modulation technique was applied to investigate the nonlinear optical properties of Tris(2`, 2-bipyridyl)iron(II) tetrafluoroborate solution. The obtained results show a strong pump laser beam (λ = 532 nm) that could modulate a weak probe laser (λ = 635 nm), indicating for new applications in nonlinear optical modulation. The temporal evolutions of diffraction rings were recorded, at the same time, the collapse effect was observed. Furthermore, our results led to evaluate many nonlinear parameters: the nonlinear refractive index (n2), Δn and thermo-optic coefficient (dn/dT). Our sample is candidate for all-optical switching devices.

Nonlinear optical effect and nonlinear optical mass sensor based on graphene optomechanical system

Graphene, atomically thin two-dimensional (2D) nanomaterial consisting of a single layer of carbon atoms, has received tremendous attention in the past few decades. Graphene may be considered as an excellent nanomaterial for fabricating nanomechanical resonator systems to investigate the quantum behavior of the motion of micromechanical resonators because of its unique properties of low mass density, high frequency, high quality-factor, and intrinsically small size. Additionally, graphene optomechanics based on a bilayer graphene resonator coupled to a microwave on-chip cavity, where light and micromechanical motion interact via the radiation pressure, has been demonstrtated experimentally recently. In this work, we demonstrate theoretically the nonlinear optical effect including optical bistability and four-wave mixing under the regimes woth different parameters and detunings in a graphene resonator-microwave cavity system. When the graphene optomechanics is driven by one strong pump laser beam, we find that the optical bistability can be controlled by tuning the power and the frequency of the pump beam. The four-wave mixing (FWM) phenomenon is also investigated and we find that sharp peaks in the FWM spectrum exactly are located at the resonant frequency of graphene resonator. Therefore, a straight nonlinear optical means for determining the resonant frequency of the graphene resonator is presented. Setting the cavity field resonating with pump field, and then scanning the probe frequency across the cavity frequency, one can easily and exactly obtain the resonant frequency of the resonator from the FWM spectrum. We further theoretically propose a mass sensor based on the graphene optomechanical system. The mass of external nanoparticles deposited onto the graphene resonator can be measured conveniently by tracking the shift of resonant frequency due to mass changing in the FWM spectrum. Compared with optomechanical mass sensors in linear regime, the nonlinear optical mass sensor may be immune to the detection noise. The system may have potential applications in communication networks for frequency conversion and provide a new platform for high sensitive sensing devices.

A tunable Doppler-free dichroic lock for laser frequency stabilization

We propose and demonstrate a laser frequency stabilization scheme which generates a dispersion-like tunable Doppler-free dichroic lock (TDFDL) signal. This signal offers a wide tuning range for lock point (i.e. zero-crossing) without compromising on the slope of the locking signal. The method involves measurement of magnetically induced dichroism in an atomic vapour for a weak probe laser beam in presence of a counter propagating strong pump laser beam. A simple model is presented to explain the basic principles of this method to generate the TDFDL signal. The spectral shift in the locking signal is achieved by tuning the frequency of the pump beam. The TDFDL signal is shown to be useful for locking the frequency of a cooling laser used for magneto-optcal trap (MOT) for $^{87}Rb$ atoms.

Controllable four-wave mixing based on mechanical vibration in two-mode optomechanical systems

We theoretically investigate the four-wave mixing (FWM) process in a two-mode cavity optomechanical system, where two cavity modes are coupled to a common mechanical resonator. The left cavity is driven by a strong pump laser beam and a weak probe laser beam simultaneously, but the right cavity is only driven by a strong pump laser beam. It is shown that when both cavities are driven at their respective red sidebands, optomechanically induced transparency (OMIT) appears and FWM is resonantly enhanced with reduced linear absorption. However, when the left cavity is driven at its red sideband but the right cavity is driven at its blue sideband, robust photon entanglement can be realized (Tian L., Phys. Rev. Lett., 110 (2013) 233602). In this case, the FWM intensity can be increased by three orders of magnitude at lower pump power.

Nonlinear focusing of weak beam by another high power laser

In this paper, we theoretically and experimentally investigate the controllable nonlinear focusing of the weak laser beam on the basis of the induced nonlinear effects by another strong pump laser beam. When couple laser beams co-propagate in the Kerr medium, it is possible to change the refractive index by the pump beam, and the locally changing medium in turn modifies the weaker probe beam. Depending on cross-phase modulation theory, we obtain an exact analytical solution to the model under the approximate condition and qualitatively verify it in experiment. The results show that the weaker probe beam can be induced to focus at any position due to induced nonlinear effects from the stronger pump beam under certain conditions.

Generation of optical vortices using light-induced phase mask in a V-type system

We experimentally demonstrated that optical vortices with opposite charges could be generated on a probe beam transmitted through a medium composed of rubidium atoms with V-type energy levels when the refractive index of the medium was modified by a strong pump laser beam with an L-shape intensity distribution.

EXPERIMENT AND THEORY ON DIFFRACTION FROM LASER-INDUCED PHASE-HOLE IN POLYMER FI LM

Concentric diffraction rings with bright center in the far field and dark center in the near field of the probe beam were experimentally observed when a strong pump laser beam (526nm) and a weak probe laser beam (632.8nm) cross under the no nlinear medium film (Polypyrrylarylenemethine/polyvinyl film).Based on Fresnel-K irchhoff diffraction integral equation,this phenomenon can be explained by the d iffraction effect of the probe beam from the laser-induced phase-hole in the non linear medium caused by the pump beam.The numeric calculations give good agreeme nt with the experimental results.

Pump-probe spectroscopy of solids with excitation dependent dephasing

The paper provides a new example of the failure of optical Bloch equations in the description of coherent excitation of solids. We consider the absorption spectra of the modulation side bands of a strong pump laser beam in low-temperature solids. The influence of the pump on the impurity-ion dipole dephasing is taken into account. It is shown that a rectangular shaped hole is restored in the absorption spectrum when the Rabi frequency exceeds the fluctuation rate of the local random field responsible for the impurity-ion dephasing.

K2optically pumped lasers using temporally delayed pulses in the counterintuitive sequence

We report increased stimulated emission on some optically pumped laser transitions coupled to suppressed stimulated emission on other transitions when a weak Stokes laser beam and a strong pump laser beam interact with K2 molecules in the counterintuitive sequence. The Stokes laser photons begin to interact with the K2 molecules 3 to 4 ns before the pump laser photons can interact with the K2 molecules. Both the Stokes and the pump laser pulses last for approximately 5 ns and the suppressed and enhanced stimulated emissions coincide with the pump laser pulse. The stimulated emissions described in this paper propagate parallel to the Stokes and pump laser beams.

A simple technique for separation of laser beams in collinear frequency mixing

Ingenious selection of an appropriate dispersive prism has enabled us to separate physically the strong pump laser beam from the closely spaced nonlinear generated frequencies, thereby avoiding use of delicate interference filters. The principle has been successfully tested in nonlinear experiments.