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Introduction to the NHMFL Pulsed Field Facility at LANL

Information on the physical set-up of pulsed field measurements

Read about lock-in amplifiers and their role in your measurements

Information about noise and ways to eliminate it from your measurements

How to collect and evaluate your measurement data

Information on optical spectroscopy

Information about time-resolved optics

Information on de Haas van Alphen Effect measurements

Information on Shubinkov de Haas Effect measurements

Information on Absolute Resistivity measurements

Information on Heat Capacity measurements

Information on RF Penetration Depth measurements

Ways to Reduce Noise Checklist


LOCK-IN AMPLIFIER METHODS

_____ Increase the averaging time carefully, without overloading the lock-in input. See Phase Shifts and Overloading

_____ Increase the current through the sample in order to maximize the signal to noise ratio, but be sure not to heat the sample. See Current

_____ Try a different oscillator frequency in an attempt to find lower interference. See Current

_____ For quasi-1D charge density wave, spin density wave, use a higher frequency because such systems respond differently to low frequency signals. See Current

_____ Very high resistance samples need a lower frequency, because cable and other reactance begins to have a higher effect at higher frequencies. See Current

_____ One of the biggest problems is overload of the lock-in. If this happens, try decreasing the lock-in sensitivity. See Phase Shifts and Overloading

MECHANICAL DAMPING TO REDUCE VIBRATION-INDUCED SIGNALS IN LARGE FIELDS:

_____Bring helium out of superfluid state. Normal-state helium damps out vibrations better than superfluid helium. See Mechanical Noise

_____Fasten probe wires over probe with GE varnish for as much of their length as possible, especially near the sample. See Mechanical Noise

CAPACITIVE/INDUCTIVE INTERFERENCE REDUCTION METHODS

_____ Pay careful attention to grounds and voltage drops along small-gauge shields on ground returns. See Ground Loops

_____Unplug all unnecessary electronics before the pulse. including the LR-700, and any computers that may have been used for cool down curves. Also move wires away from the magnet, and other potential noise sources. See External Noise and Coupling Noise

_____Filter with Stanford SR560 pre-amp or design own filters. See Filtering

NOISE REDUCTION METHODS

_____1/f noise is decreased at higher f. This only becomes important if you have minimized all interference sources and have already obtained a very high signal to noise ratio. Typical 1/f knees can be as low as a few hertz or as high as 40kHz in some ultra-low-noise op-amps. See Intrinsic Noise

SAMPLE MOUNTING

_____Excessive contact resistance can degrade signal to noise ratio, this is especially true for very low resistance samples. Be sure sample is mechanically constrained and that thermal contact is correct for the measurement. See Sample Contact Resistance

SOFTWARE METHODS

_____ Limiting, averaging and band-pass filtering can often be achieved via software.