This course begins with a general introduction to laser amplifiers, explaining the basic physical principles and properties of amplifiers, including e.g. four-level vs. quasi-three-level gain media, gain saturation in steady state and in pulse amplification, and amplified spontaneous emission (ASE). It then continues with more specific details for fibre amplifiers, including an overview on different amplifying ions and host media, double-clad fibres, mode areas, effective transition cross sections, influence of the pump wavelength, and ASE limitations. After a discussion of continuous-wave amplification, specific issues of pulse amplification will be discussed for the pulse duration regimes of nanoseconds, picosecond and femtoseconds. Finally, a brief overview on the physical modelling of amplifiers will be given.
We perform third harmonic spectroscopy of dolmen-type nanostructures, which exhibit plasmonic Fano resonances in the near-infrared. Strong third harmonic emission is predominantly radiated close to the low energy peak of the Fano resonance. Furthermore, we find that the third harmonic polarization of the subradiant mode interferes destructively and diminishes the nonlinear signal in the far-field. By comparing the experimental third harmonic spectra with finite element simulations and an anharmonic oscillator model, we find strong indications that the source of the third harmonic is the optical nonlinearity of the bare gold enhanced by the resonant plasmonic polarization.
At PTB we have performed a comparison between a 171 Yb + single ion clock (octupole transition) and a 87 Sr clock interrogating an ensemble of atoms captured in an optical lattice.
Localized surface plasmon (LSP) resonances provide a means by which optical energy can be converted to electrical energy and manipulated. Configurations of metal nanostructures can be used to modify the properties of light, due to interactions between the LSP mediated by their evanescent electric fields. Such configurations can be thought of as nanophotonic circuits and it is possible to create optical analogues of electrical circuits that are sensitive to phase. We have developed a simple analytical model that enables us to understand the optical properties of ensembles of nanostructures. The method has been used to design an optical equivalent of the AC Wheatstone bridge circuit with a size scale typically 100 nm. This has applications in sensing and optical signal processing.
We report, to the best of our knowledge, the shortest period for a femtosecond direct-write waveguide Bragg grating. Waveguide Bragg-gratings with a period of 270 nm have been fabricated in boro-aluminosilicate glass showing a 5 dB strong 1st order resonance at 800 nm.
In this paper, we theoretically investigate how the momentum width of an atomic source affects the efficiency of Bragg beam splitters and mirrors. We conclude that narrow momentum width sources, such as atom lasers, are significantly more efficient than atomic clouds with a larger momentum width, such as thermal sources, for high (but accessible) order Bragg processes. The development of large momentum transfer (LMT) mirrors and beam splitters is one of the most promising paths leading to increased precision in future sensors based on atom interferometry. This makes these results significant, because the signal to noise ratio of an interferometric measurement scales linearly with the momentum imparted in the beam splitting processes and scales as the square root of the atomic flux.
We examine the guiding mechanism of photonic crystal (PC) waveguide modes through the properties of their evanescent fields in the photonic crystal cladding, allowing an unambiguous definition of gap-guided and index-guided modes. We show that the ability to tailor the dispersion of PC waveguide modes depends on the properties of these fields. Our analysis suggests that the photonic crystal's lattice type can be used to maximize the region of the Brillouin zone where PC waveguide modes can be dispersion engineered.
Recent advances in atom optics and atom interferometry have enabled observation of atomic de Broglie wave interference when atomic wavepackets are separated by distances exceeding 50 cm and times of 2 seconds [1]. With further refinements, these methods may lead to meter-scale superpositions. In addition to providing new tests of quantum mechanics, these methods allow inertial force sensors of unprecedented sensitivity. We will describe methods demonstrated and results obtained in a 10 m atomic fountain configuration, their implications for technological applications in geodesy, and their relevance to fundamental studies in gravitational physics. We will describe how entangled atomic ensembles can be used to obtain further performance gains, following our demonstration of 18 dB measurement noise reduction using spin-squeezed atomic states [2].
We report novel effect of solvents on optical coherence properties of CdSe/ZnS semiconductor quantum dots (QDs) in solution detected by femtosecond four-wave mixing (FWM) spectroscopy. The FWM signals of QDs show different time profiles and femtosecond coherence decays in three solvents. Our findings provide definite evidence that the interaction with solvent molecules predominantly determines optical coherence and line broadening properties of QDs in solution.
Nature of light as an electromagnetic wave with transverse components has been confirmed using optical polarizers, which are sensitive to the electric field orientation only. Recent advances in optical technologies in nanometer scale demand their magnetic counterpart: optical magnetic polarizers. Here we experimentally establish the optical magnetic field polarization as a separate entity from the electric field polarization by showing that subwavelength circular metallic apertures predominantly sense the magnetic field component of light.
We investigate theoretically the possibility of the excitation of a confined state of the electromagnetic field at the metal-less structures, which can be referred to as optical Tamm plasmons. In contrast to the ordinary surface plasmons, Tamm plasmons can be formed with either s- or p- polarization and its dispersion lies within the light cone, and thus it can be optically excited without the structure of prisms or gratings. In this study, we calculate the reflectance and electromagnetic field distributions of both s and p waves incident on metal-less systems in a numerically exact manner, using the invariant imbedding method of wave propagation in linear and nonlinear stratified media. We have observed the dip of the reflectance for the both s and p wave cases. We show that the electromagnetic field enhancement and the influence of nonlinearity due to the excitation of Tamm plasmons are much stronger than those due to conventional surface plasmons.
We demonstrate the generation of polarization-entangled photon pairs at telecommunication wavelengths with type-II quasi-phase matched spontaneous parametric down-conversion (QPM-SPDC) having two poling periods. The generated two-photon polarization state was analyzed by the quantum state tomography.
A selective synthesis method of silver nanoparticles in pre-patterned trenches is presented. In order to show their potential applications of plasmonic devices, we characterized their localized surface plasmon resonances by measuring far- and near-field intensities.
We have preformed femtosecond time-resolved coherent anti-Stokes Raman spectroscopy (CARS) to study the vibrational dynamics in polymethylmethacrylate (PMMA) film. We measured the coherent vibrational relaxation rates of CH2 symmetric and CH2 anti-symmetric stretch modes (at 2750 cm-1 and 2950 cm-1) and observed the CARS signal beats between CH2 stretch modes in PMMA. Numerical fitting involving two contributions provided the coherent vibrational relaxation time for each stretch mode. The coherent vibrational relaxation of antisymmetric mode in PMMA was found much faster than that of symmetric mode.
The magnetic components of light have in general not been a popular subject compared to the electric ones. However, recent researches of light-matter interaction stress the importance of the magnetic field for optical properties of nanostructure. In this study, we investigated the magnetic light-matter interaction with subwavelength metallic single holes. We find the optical properties of tiny metallic single holes are entirely determined by the interaction with the magnetic field of light as postulated by Bethe.
In this study, we propose a high quality (Q) factor nanocavity in a rod-type photonic crystal slab structure for controlling TM light. By analyzing the dispersion relations of the rod-type photonic crystal waveguides, we design a heterostructure nanocavity consisting of many waveguides with different lattice constants. The Q factor of the nanocavity is as high as 470,000, and its modal volume is as small as 0.7(λ/n)3. Furthermore, we investigate the influence of asymmetrically and symmetrically low-index-clad structures on the Q factor of the cavity.
The realization of quantum information processing requires sophisticated fabrication methodologies of its constituents. In this work we demonstrate the fabrication of micron size diamond microdisks from single crystal diamond. Photoluminescence measurements confirm the presence of nitrogen vacancy centers and show the propagation of whispering gallery modes. Such structures are promising for the realization of diamond integrated quantum photonics devices.
We show the first demonstration of two-dimensional Anderson localization (AL) of light in planar random photonic crystals, with direct near-field imaging by use of SNOM (Scanning Near-field Optical Microscope). We demonstrated two-dimensional random photonic crystal lasers to which structural randomness was introduced by carefully dislocating the positions of air holes. We show that only slight amount of randomness induces the extended Slow Bloch Modes to become Anderson localized. Furthermore, we perform FDTD (Finite-Difference Time-Domain) computation algorithm to confirm the experimental results to be consistent with theoretical predictions. Our results, for the first time, spatially resolve a two-dimensional AL in the disordered photonic band gap structure by near-field imaging.
Optical complex electric field spectra of a 400 GHz optical frequency comb were controlled by a colorless optical synthesizer. The synthesized 2 Tb/s signals were measured by a proposed digital holographic optical frequency comb analyzer.
