Disclosed is a refrigerator having a sensor cover slidingly-coupled to inside of a cooling chamber and accommodating a sensor therein. The microfeature dies can include a substrate having a bond site and integrated circuitry electrically connected to the bond site. If the calculated gradient adjustment is greater than a first threshold amount, an adjustment is performed of the standard deviation of the mixture component using the first threshold. By frequency shifting the light fields with frequency shifting means in the reference and sample arm a phase resolved signal at high speed can be registered.