The top 500 results for ""T Hänsch"" are:

By means of pulsed laser spectroscopy applied to muonic hydrogen (μ⁻ p) we have measured the 2S^{F = 1}_1/2 – 2P^{F = 2}_3/2 transition frequency to be 49881.88(76) GHz [1]. By comparing this measurement with its theoretical prediction [2, 3, 4, 5, 6, 7] based on bound-state QED we have determined a proton radius value of r_p = 0.84184(67) fm. This new value differs by 5.0 standard deviations from the COD ATA value of 0.8768(69) fm [8], and 3 standard deviation from the e-p scattering results of 0.897(18) fm [9]. The observed discrepancy may arise from a computational mistake of the energy levels in μp or H, or a fundamental problem in bound-state QED, an unknown effect related to the proton or the muon, or an experimental error.

We have observed the reflection of a probe laser beam by a three-dimensional optical lattice of rubidium atoms. The reflection spectrum shows different kinds of narrow resonances which we attribute to degenerate (phase conjugation) and non-degenerate multiwave mixing processes. In order to explain the extremely narrow linewidth (300 Hz) of the degenerate four-wave mixing resonance and its dependence on the angle of incidence of the probe, we propose a novel physical mechanism which includes the formation of a long-range atomic-density grating acting as a hologram.

We present a toolbox for cold atom manipulation with time-dependent magnetic fields generated by an atom chip. Wire layouts, detailed experimental procedures and results are presented for the following experiments: use of a magnetic conveyor belt for positioning of cold atoms and Bose–Einstein condensates (BECs) with a potential resolution of 2 nm; splitting of thermal clouds and BECs in adjustable magnetic double-well potentials; and controlled splitting of a cold reservoir. The devices that enable these manipulations can be combined with each other. We demonstrate this by combining reservoir splitter and conveyor belt to obtain a cold atom dispenser. We discuss the importance of these devices for quantum information processing, atom interferometry and Josephson junction physics on the chip. For all devices, absorption-image video sequences are provided to demonstrate their time-dependent behaviour.

The double response of a large area avalanche photodiode, a planar RMD model S1315, to 6-keV x-rays was investigated as a function of APD biasing voltage and for different operating temperatures. Our data are consistent with the interpretation that the dissimilar APD response is due to x-ray interactions in the different APD-layer structures; interactions in the APD entrance layer just below the front electrode, where the electric field intensity is very low lead to pulses with higher risetime and lower amplitudes, when compared with interactions in the deeper layers where the electric field is more intense. Average pulse risetime values of 14 and 7 ns have been measured in our setup, the slower pulses presenting average amplitudes which are around 20% lower than those of the faster pulses. While the fast risetime does not depend significantly on APD biasing voltage and on temperature, the slow risetime presents a slight decrease with increasing bias voltage and decreasing temperature, a behaviour that is consistent with the increase of the electric field as a result of the increase in the APD biasing voltage. The fraction of the slow pulses reduces from 60% to 40% as the APD biasing increases from about 1.58 to 1.64 kV, indicating a reduction in the thickness, from 25 to 15 μm, in the weak-electric-field entrance layer.

An assortment of photonic-crystal fibers with a core area varying from 20 to 50 μm² is used to demonstrate efficient frequency conversion of megawatt femtosecond Cr:forsterite laser pulses with a central wavelength of 1.24 μm into the visible and infrared spectral ranges. Supercontinuum radiation with a spectrum spanning from 500 to 1800 nm and total output energy of hundreds of nanojoules is observed at the fiber output.

An investigation was made of the competition between the λ₀ = 3.3912 μ and λ₁ = 3.3922 μ lines emitted by a helium–neon laser. The theoretical output power at the wavelength λ₁ was found to be 50% of the output at λ₀. The experimental value was 40%. The rate of decay of the lower level of the λ₁ line was determined and it was found that the rates of decay of the lower levels of both lines were independent of the pressure.

A solution to the key problem of femtosecond metrology — elimination of the frequency offset related to the intracavity dispersion of a femtosecond laser — is proposed. The proposed method involves stabilisation of the intermode interval between equidistant spectral components in a frequency comb produced by a mode-locked femtosecond laser by phase-locking the frequency difference between a pair of discrete spectral components in this comb to the frequency of a reference laser. An introduction of a nonlinear-optical crystal for frequency doubling into the scheme for frequency-comb stabilisation allows the frequency offset related to the intracavity dispersion of the femtosecond laser to be eliminated, thus suggesting the way for absolute stabilisation of frequency combs generated by femtosecond mode-locked lasers. Radiation of a reference laser with such an approach plays the role of an anchor in the femtosecond clockwork.

Microstructure optical fibres with a cladding consisting of a single cycle of air holes and the minimum core diameter of 1 μm have been fabricated and studied. Guided modes supported by this fibre are characterised by a high light localisation degree and display the C_6ν point-group spatial symmetry of the transverse field distribution. A high refractive index step between the core and the cladding in the created fibres strongly confines the light field in the fibre core. The spectral broadening of low-power femtosecond laser pulses in the fibre of this type is experimentally studied.

The mode structure of supercontinuum emission generated by femtosecond pulses of Ti:sapphire laser radiation in microstructure fibres is studied. The long-wavelength (720 — 900 nm) and visible (400 — 600 nm) parts of supercontinuum are shown to be emitted in spectrally separable isolated spatial modes. These spectrally sliced single modes of supercontinuum emission possess a high spatial quality, verified by efficient nonlinear-optical frequency conversion.

The emission spectrum of a femtosecond Ti:sapphire laser broadened in a tapered optical fibre and the shape of its envelope are studied as functions of the waist diameter and the laser power coupled to the fibre. By varying the fibre parameters and characteristics of coupled pulses, the envelope of the broadened emission spectrum can be shaped, which is important in using a femtosecond comb for precision measurements. The results of experimental studies of the temporal structure of a supercontinuum in a tapered fibre obtained by using the sum frequency generation are presented for the first time and theoretically interpreted.