95 GHZ SPECTROMETER CW LOCK-IN DEMODULATOR UPGRADE

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This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. Continuous-wave spectroscopy with our ACERT 95 GHz instrument has previously utilized a single lock-in amplifier (SRS 510) for detection of the spectral lineshape. We are presently upgrading this subsystem to a digital signal processor (DSP) based lock-in (Stanford Research Systems 850) which offers a number of significant performance advantages over the previous unit. The DSP-based unit has higher dynamic reserve, lower drift, lower distortion and dramatically higher phase resolution than the conventional analog lock-in it is replacing. Additionally, due to the unit's built-in display and processing capabilities, data may be presented to the experimentalist in a range of operationally-useful formats unavailable with the previous lock-in system. The DSP unit graphical display will also facilitate setup and analysis of frequency-modulation detection for FM development work and for broad-line specimens. Integration of the new DSP lock-in amplifier into the 95 GHz spectrometer and implementation of its I/O functions into routines of the spectrometer control system requires modest revision of the control system software. Accordingly, new Python scripting routines are being written prior to replacing the former lock-in with the new DSP system. When the new routines are completed and debugged, we will transfer the spectrometer's c.w. line detection scheme from its existing analog lock-in detector to the DSP lock-in.