ABSTRACT
A dichroic atomic vapor laser lock (DAVLL) system exploiting buffer-gas-filled millimeter-scale vapor cells is presented. This system offers similar stability as achievable with conventional DAVLL system using bulk vapor cells, but has several important advantages. In addition to its compactness, it may provide continuous stabilization in a multi-gigahertz range around the optical transition. This range may be controlled either by changing the temperature of the vapor or by application of a buffer gas under an appropriate pressure. In particular, we experimentally demonstrate the ability of the system to lock the laser frequency between two hyperfine components of the (85)Rb ground state or as far as 16 GHz away from the closest optical transition.
ABSTRACT
We show the operation of an optically pumped magnetometer array in a 50 µT magnetic field. The various components for a fully optical and non-magnetic detector unit were constructed and evaluated, from which a prototype unit was assembled with fiber coupled electronics. In this unit the magnetometers were operated using the intensity modulated method and heated with an off-resonant laser. Calculations on the temperature distribution were used to design the magnetometer array. Different magnetometers in such a detector unit were characterized and showed identical performance. Without applying noise reduction schemes, the obtained magnetic field resolution is a factor 2.5 above the shot noise level down to frequencies of about 7 Hz.
ABSTRACT
Differential bipolar sensing was evaluated in 10 consecutive patients with symptomatic heart block managed with dual chamber pacing. During pacemaker implantation atrial and ventricular electrograms were recorded using unipolar (UP) and differential bipolar (DBP) sensing amplifiers. The mean peak-to-peak amplitudes of the UP and DBP atrial electrograms were 3.3 +/- 1.2 mV and 4.2 +/- 1.2 mV, respectively. The difference was statistically significant (p less than 0.05). The mean peak-to-peak amplitudes of the ventricular electrograms were, respectively, 6.8 +/- 1.5 mV and 7.5 +/- 1.4 mV (p less than 0.01). Within 6 weeks after pacemaker implantation, patients visited the outpatient clinic. Isometric exercise tests were performed during UP and DBP sensing of the pacing system. Myopotential sensing in the ventricle occurred in nine patients during UP sensing and in none of the patients during DBP sensing (p less than 0.01) at a sensitivity setting of 0.5 mV. In addition, chest wall stimulation was performed to assess the effects of far-field signals on the ventricular sensing circuit of the pulse generator. Chest wall stimuli inhibited ventricular output during UP sensing in all 10 patients, whereas during DBP sensing inhibition of the ventricular channel occurred in three patients and then only at high output (greater than 8 V) settings. The susceptibility of the pacing system to crosstalk was also determined. However, neither during UP sensing nor during DBP sensing could cross-stimulation or cross-inhibition be demonstrated. In conclusion, DBP sensing is superior to UP sensing in terms of myopotential and far-field sensing.(ABSTRACT TRUNCATED AT 250 WORDS)
