A new scheme for temperature measurements in a magneto-optical trap is reported.It allows non-destructive on-line measurements of spring constant, friction coefficient, and temperature in a magneto-optical trap. By this method, sub-Doppler temperatures as low as 20pK have been measured on-line in a rubidium trap.Introduction. -For many purposes in spectroscopy and atomic physics in general it is desirable to have atomic samples with very low velocities confined to a well-defined small volume. Thus in the recent past tremendous efforts have been undertaken in laser cooling and trapping. Raab et al. [l] reported the first magneto-optical trap (MOT), which employs the Zeeman-and Doppler-effects to exert position-and velocity-dependent light pressure on atoms. Since the introduction of vapour cell MOTS by Monroe et al. E23 these devices have gained widespread interest. The lower bound for the temperature T of optically trapped two-level atoms is the so-called Doppler limit TD = h .I'/2kB (140 pK for Rb) where r is the natural linewidth of the cooling transition (Rb: r = 2x-5.9 MHz). Sub-Doppler temperatures, first measured in molasses by Lett et al. [3], have been explained by Dalibard and Cohen-Tannoudji[43 by the non-adiabatic motion of (real) multilevel atoms through the optical-polarization gradient in molasses. The first measurements of sub-Doppler temperatures in a caesium MOT were published by Steane and Foot[5].We report here about the operation of a magneto-optical rubidium trap. We found sub-Doppler temperatures using a new simple technique of measuring the mechanical properties of the MOT.Apparatus. -A stainless-steel vacuum chamber with a capacity of 11 is pumped by a 21 / s ion getter pump and a 300 cm2 ST 707 getter strip. The pressure inside the ion getter pump is (*) Now with Deutsche Forschungsanstalt fiir LUR und Raumfahrt (DLR), I"-AUG, Sudstral3e 125, D-W 5300 Bonn 2, Germany.

No abstract

Two different isotopes-(85)Rb and (87)Rb-have been captured simultaneously in one magneto-optical trap. The trap parameters could be chosen nearly independently for the two isotopes. The trap loss rates that are due to collisions between atoms of different isotopes have been measured in the low-intensity limit.

We present a feasibility study into laser treating dental materials by using femtosecond pulses generated by a titanium:sapphire laser system which consisted of an oscillator and a regenerative amplifier. The pulse duration was varied between 200 fs and 2 ps. The observed energy thresholds for the ablation process of dentine and enamel were clearly smaller than those observed when longer pulse durations were used. The consequence of this observation is a lower thermal load within the vicinity of the radiated area. Thus no thermal damage or mechanical damage, such as cracks, were produced during the laser treatment. Commercially available femtosecond laser systems can produce ablation rates in healthy and in-vitro demineralized dental material 2 mm3 per min and 6-16 mm3 per min, respectively. These values are an order of magnitude larger than those produced by picosecond laser systems at the same time pulse energy and pulse repetition rate. The brightness of the plasma spark generated by the laser treatment depended on the dimineralization of the teeth. This may allow online control of the laser treatment.

No abstract