A gain and bandwidth enhanced transimpedance preamplifier for Fourier-transform ion cyclotron resonance mass spectrometry

The nature of the ion signal from a 12-T Fourier-transform ion cyclotron resonance mass spectrometer and the electronic noise were studied to further understand the electronic detection limit. At minimal cost, a new transimpedance preamplifier was designed, computer simulated, built, and tested. The preamplifier design pushes the electronic signal-to-noise performance at room temperature to the limit, because of its enhanced tolerance of the capacitance of the detection device, lower intrinsic noise, and larger flat mid-band gain (input current noise spectral density of around 1 pA/√Hz when the transimpedance is about 85 dBΩ). The designed preamplifier has a bandwidth of ~3 kHz to 10 MHz, which corresponds to the mass-to-charge ratio, m/z, of approximately 18 to 61 k at 12 T. The transimpedance and the bandwidth can be easily adjusted by changing the value of passive components. The feedback limitation of the circuit is discussed. With the maximum possible transimpedance of 5.3 MΩ when using an 0402 surface mount resistor, the preamplifier was estimated to be able to detect ~110 charges in a single scan.     

Performance of a circle-to-line optical system for a Fabry-Perot interferometer: a laboratory study

We describe the characterization and laboratory study of a new optical device, a circle-to-line interferometer optical (CLIO) system, for a Fabry-Perot interferometer. The CLIO system converts a circular Fabry-Perot interferometer fringe pattern into a linear fringe pattern that can be analyzed by a linear array detector or a charge-coupled device. One can achieve the circle-to-line conversion by the use of a mirrored kaleidoscope and a 90-deg segment of a 45-deg half-angle internally reflecting cone. Our laboratory results are in good agreement with theoretical predictions. The aberrations associated with this optical system are minor for large F-number optical systems, especially for the cone segment. The finesse degradation caused by this CLIO system is relatively small, which agrees with the results of a ray-trace study.