Frequency response measurement of high-speed photodetectors using the spectrum power method in a delay self-heterodyne system

We report on a photoionization scheme for controlled loading of ⁸⁸Sr⁺ ions into a radio-frequency (rf) ion trap. The two-step doubly-resonant process drives the ⁸⁸Sr atom on the 5s^{2 1} S ₀ – 5s5p¹ P ₁ transition at 461 nm using a frequency-doubled diode laser, and then excites the atom to the autoionizing (4d²+5p²) ¹ D ₂ state with 405 nm light from a free-running diode laser. This method of trap loading is quantitatively compared to electron bombardment loading, and shown to reduce the Sr vapour pressure required to load by four orders of magnitude. It also provides more than an order of magnitude reduction in the day-to-day variation of the voltages required to compensate micromotion. We additionally introduce a two-step atomic source consisting of an oven and hotplate, which reduces the number of impurities evaporated towards the trap. This is shown to significantly reduce fluctuations in required micromotion compensation voltages. The demonstrated reduction in flux and increased source purity are expected to improve the reliability of trap operation for precision ion-trap experiments. PACS 32.80.Fb; 32.80.Pj; 39.10.+j     

Simple and efficient magnetic transport of cold atoms using moving coils for the production of Bose–Einstein condensation

We have developed a simple magnetic transport method for the efficient loading of cold atoms into a magnetic trap. Laser-cooled ⁸⁷Rb atoms in a magneto-optical trap (MOT) are transferred to a quadrupole magnetic trap and they are then transported as far as 50 cm by moving magnetic trap coils with a low excess heating of atoms. A light induced atom desorption technique helps to reduce the collision loss during the magnetic transport. Using this method, we can load cold ⁸⁷Rb atoms into a magnetic trap in an ultra high vacuum chamber with high efficiency, and we can produce ⁸⁷Rb condensate atoms. PACS 39.25.+k; 32.80.Pj; 03.75.Pp     

Microscopic electro-optical atom trap on an evanescent-wave mirror

We put forward the idea of a surface-mounted microscopic electro-optical atom trap. The trap is formed on an evanescent-wave atom mirror by the strongly localized static electric field of two oppositely charged transparent electrodes placed close to each other. The electrodes are embedded in a refractive-index-matched thin dielectric layer on the surface of a glass prism. In our example, the phase-space density in the trap center reaches 0.1, when the trap is loaded with atoms from a gravito-optical surface trap.Received: 16 October 2003PACS: 32.80.Pj Optical cooling of atoms; trapping - 39.25. + k Atom manipulation (scanning probe microscopy, laser cooling, etc.)     

Laser cooling of Cd<Superscript>+</Superscript> ions using a microwave transition as a repumping process

Cadmium ions trapped in a linear Paul trap have been laser cooled by use of a microwave transition as a repumping process. A 15.2-GHz microwave transition between a ground-state hyperfine splitting is used for repumping, while an all-solid-state laser with the wavelength of 214 nm drives the cooling transition between the ² S _1/2 and ² P _3/2 states. A phase transition from the cloud state to the crystal state of trapped ions has been observed both in fluorescence spectra and in images of an ion string. Cadmium ions have potential of application for quantum information processing where the ground-state microwave transition is used for both a repumping process and manipulation of quantum states of trapped ions. PACS 32.80.Pj     

Selective loading and laser cooling of rare calcium isotope 43Ca+

We report a method for loading ⁴³Ca⁺ ions selectively in a linear Paul trap using ultraviolet light-emitting-diodes (LEDs) for the second excitation in a two-step photo-ionization process. The difficulty in working with ⁴³Ca⁺ is its low natural abundance (0.135%). In order to load ⁴³Ca⁺ selectively, we utilize the isotope shifts for the 4s^{2 1} S ₀–4s4p¹ P ₁ transition of neutral calcium atoms. We discuss the limitation of the selectivity of the employed photo-ionization scheme and observe spectra from unwanted isotopes as well as that from ⁴³Ca⁺. Purification of ⁴³Ca⁺ is performed by adjusting the detuning of the cooling laser frequency and trapping potential. The method of loading and purification can be used in the application of trapped ⁴³Ca⁺ for an optical frequency standard and for quantum information processing. PACS 32.80.Fb; 32.80.Pj     

Improved atom number with a dual color magneto-optical trap

We demonstrate a novel dual color magneto–optical trap (MOT), which uses two sets of overlapping laser beams to cool and trap 87 Rb atoms. The volume of cold cloud in the dual color MOT is strongly dependent on the frequency difference of the laser beams and can be significantly larger than that in the normal MOT with single frequency MOT beams. Our experiment shows that the dual color MOT has the same loading rate as the normal MOT, but much longer loading time, leading to threefold increase in the number of trapped atoms. This indicates that the larger number is caused by reduced light induced loss. The dual color MOT is very useful in experiments where both high vacuum level and large atom number are required, such as single chamber quantum memory and Bose–Einstein condensation (BEC) experiments. Compared to the popular dark spontaneous-force optical trap (dark SPOT) technique, our approach is technically simpler and more suitable to low power laser systems.     

Experimental Improvement of Signal of a Single Laser-Cooled Trapped ^40Ca^＋ Ion

A single ^40Ca^＋ ion is loaded in a miniature Paul trap and the probability of directly loading a single ion is above 50%. The signal-to-noise ratio and the storage time for a single ion have been improved by minimizing the ion micromotion and locking a 397nm cooling laser to a Fabry-Perot interferometer and optogalvanic signal. From the fluorescence spectrum, the ion temperature is estimated to be about 5mK.     

Optimized production of a cesium Bose–Einstein condensate

We report on the optimized production of a Bose–Einstein condensate of cesium atoms using an optical trapping approach. Based on an improved trap loading and evaporation scheme we obtain more than 10⁵ atoms in the condensed phase. To test the tunability of the interaction in the condensate we study the expansion of the condensate as a function of scattering length. We further excite strong oscillations of the trapped condensate by rapidly varying the interaction strength. PACS 03.75.Kk; 32.80.Pj     

Compact and robust laser system for rubidium laser cooling based on the frequency doubling of a fiber bench at 1560 nm

We propose a new compact and reliable laser system for rubidium laser cooling in onboard experiments like atomic clocks or atomic inertial sensors. The system is based on the frequency doubling of a telecom fiber bench at 1560 nm. Fiber components at 1560 nm allow us to generate the repumping laser and to control dynamically the power and the frequency of the 780 nm laser. With this laser system, we obtain a magneto-optical trap of ⁸⁵Rb even in the presence of mechanical vibrations and strong thermal variations (12 °C in 30 min). PACS 32.80.Pj; 42.60.-v; 42.81.Wg; 42.65.Ky; 39.20.+q     

Doppler cooling a single Ca+ ion with a violet extended-cavity diode laser

We present a scheme for employing a violet extended-cavity diode laser in experiments with single, trapped ions. For this the grating-stabilised laser is spatially and spectrally filtered and referenced to a Fabry–Pérot cavity. We measure an upper limit to the line width by observing a 305-kHz FWHM beat note with the second harmonic of a titanium sapphire laser. The laser is subsequently used to optically cool a single ⁴⁰Ca⁺ ion close to the Doppler limit. PACS 03.67.Lx; 32.80.Pj; 42.55.Px     

Precision spectroscopy technique for dipole-allowed transitions in laser-cooled ions

In this paper , we present a technique for the precise measurement of electric dipole-allowed transitions in trapped ions. By applying a probe and a cooling laser in quick succession, the full transition can be probed without causing distortion from heating the ion. In addition, two probes can be utilized to measure a dispersion-like signal, which is well suited to stabilizing the laser to the transition. We have fully characterized the parameters for the measurement and find that it is possible to measure the line center to better than 100 kHz with an interrogation time of 30 s. The long-term stability of the spectroscopy signal is determined by employing two independent ion trap systems. The first ion trap is used to stabilize the spectroscopy laser. The second ion trap is then employed to measure the stability by continuously probing the transition at two frequencies. From the Allan variance, we obtained a frequency instability of \(1\cdot 10^{-10}\) for an interrogation time of 1,000 s.     

Paramagnetic Faraday rotation with spin-polarized ytterbium atoms

We report the observation of paramagnetic Faraday rotation of spin-polarized ytterbium (Yb) atoms. As the atomic samples, we used an atomic beam, released atoms from a magneto-optical trap (MOT), and trapped atoms in a far-off-resonant trap (FORT). Since Yb is diamagnetic and includes a spin-1/2 isotope, it is an ideal sample for spin physics, such as quantum non-demolition measurement of spin (spin QND), for example. From the results of the rotation angle, we confirmed that the atoms were almost perfectly polarized. PACS 32.80.Bx; 32.80.Pj; 42.25.Lc     

Atom lithography with ytterbium beam

We successfully produced periodic ytterbium (Yb) narrow lines on a substrate using near-resonant laser light and the direct-write atom-lithography technique. The Yb atom is a promising material for nanofabrication using atom optics due to its electrical conductivity, the laser wavelength required for handling the atoms, the vapor pressure of the fabrication process, etc. The ¹⁷⁴Yb atoms collimated by Doppler cooling were channeled by the dipole force of an optical standing wave and then deposited onto a substrate. We clearly observed a grating pattern of Yb atoms fabricated on the substrate with a line separation of approximately 200 nm after examining the surface of the substrate with atomic force microscope. This is the first demonstration of nanofabrication using the atom-optical approach with Yb atoms. PACS 32.80.-t; 32.80.-Pj     

Measurement of Secular Motion Frequency in Miniature Paul Trap to Ascertain the Stability Parameters

40Ca＋ ions are trapped and laser cooled in a miniature Paul trap. The secular motion was observed by the radio-frequency resonance of the ion cloud and Zeeman profile sidebands of a single ion experimentally. The trap stability parameters a and q are determined with an uncertainty under 1% by the secular motion frequency measurement. The trap efficiency is 0.75. A practicable suggestion is given for the benefits of a new trap design.     

Development Towards a Laser Ion Source Trap for the Production of Exotic Species

A new type of resonance ionization laser ion source (RILIS) is presently being developed and tested at the off-line mass separator at Mainz University for future use at on-line exotic rare isotopes production facilities. For highest isobaric selectivity, this RILIS approach decouples the evaporation and ionization process. A further advantage is the generation of full temporal control of the resulting high quality ion beam. These facts are realized by a combination of atomizer – ion repeller – ion cooler and trap, which is operated together with a state-of-the-art, all solid state laser system. The principle and performance of this laser ion source trap (LIST) system are discussed applying simulation studies for the repeller-trap combination and first measurements for characterization.     

Laser developments and resonance ionization spectroscopy at IGISOL

We present an overview of recent laser ion source developments at the IGISOL facility, Jyväskylä. Technological advances in the lasers have led to a considerable increase in second-harmonic laser power with the use of intra-cavity second-harmonic generation, as well as to narrow linewidth capability by applying an injection-locking technique to a Ti:sapphire laser. The use of a diffraction grating for frequency selection in a new laser resonator has dramatically improved the wide-range tunability of the laser system, resulting in an ideal tool for the development of new ionization schemes. The role of different laser bandwidths, laser intensity and environmental broadening mechanisms on the experimental width of the measured spectral line have been studied using bismuth, silver and nickel, in the gas cell and expanding gas jet. Applications of novel ion guide nozzle design has led to remarkably collimated gas jets which overcome the current limitations in the gas cell-based laser ion source trap (LIST) method. Detailed planning is under way to optimize the new laser laboratory and laser transport path in order to fully exploit the unique opportunities afforded by the new IGISOL-4 facility.     

Extended temperature tuning of an external cavity diode laser

We describe the construction and operation of an external cavity diode laser in which the diode is cooled to -45 °C. This technique allows us to pull the wavelength of a nominally 782 nm diode to operate at 766.7 nm, a change of over 15 nm. The important aspects of our design are its ease and low cost as compared to other designs of changing the operating wavelength of laser diodes. We provide background information on thermal design with multiple TECs so the reader can extend this example for use in their own applications. PACS 42.60.By; 42.62.Fi; 32.80.Pj     

Laser ablation loading of a radiofrequency ion trap

The production of ions via laser ablation for the loading of radiofrequency (RF) ion traps is investigated using a nitrogen laser with a maximum pulse energy of 0.17?mJ and a peak intensity of about 250?MW/cm². A?time-of-flight mass spectrometer is used to measure the ion yield and the distribution of the charge states. Singly charged ions of elements that are presently considered for the use in optical clocks or quantum logic applications could be produced from metallic samples at a rate of the order of magnitude 10⁵ ions per pulse. A linear Paul trap was loaded with Th⁺ ions produced by laser ablation. An overall ion production and trapping efficiency of 10^?7 to 10^?6 was attained. For ions injected individually, a dependence of the capture probability on the phase of the RF field has been predicted. In the experiment this was not observed, presumably because of collective effects within the ablation plume.     

Observing a single hydrogen-like ion in a Penning trap at T = 4 K

We describe how a single hydrogen-like ion (C⁵⁺) is prepared, cooled with the method of resistive cooling and non-destructively detected with the image-current technique in a cryogenic Penning trap at T = 4 K. The storage time for C⁵⁺-ions in the cryogenically pumped vacuum chamber is longer than six months. The experimental techniques of preparing, cooling and detecting highly-charged ions in a Penning trap are relevant for precision experiments such as g-factor measurements, mass spectroscopy and laser spectroscopy. This revised version was published online in July 2006 with corrections to the Cover Date.     

Atom chip based fast production of Bose–Einstein condensate

We have developed a simple method for the fast and efficient production of a Bose–Einstein condensate (BEC) on an atom chip. By using a standard six-beam magneto-optical trap and light-induced atom desorption for loading, 3×10^{7 87}Rb atoms are collected within 1 s and loaded into a small-volume magnetic potential of the chip with high efficiency. With this method, a BEC of 3×10³ atoms is realized within a total time of 3 s. We can realize a condensate of up to 2×10⁴ atoms by reducing three-body collisions. The present system can be used as a fast and high-flux coherent matter-wave source for an atom interferometer. PACS 03.75.Be; 32.80.Pj; 39.25.+k