Abstract: A tunable optical band-pass device for spectrally filtering an input light beam is provided. The device includes an interferometer having two inner reflective planar surfaces that face each other and are tilted at an angle ? with respect to each other, and a translation device for adjusting a relative spacing of the two reflective surfaces, thus tuning the device to any arbitrary wavelength within a broad tuning range. The device also includes an input port for inputting the input light beam in the interferometer and having the input light beam impinge on one of the reflective surfaces at an incidence angle ? with respect thereto which is substantially larger than the tilt angle ?, and be partially reflected and partially transmitted by this surface thereby producing multiple transmitted light beams. An optical element for collecting the multiple transmitted light beams and producing a spectrally-filtered output light beam is also included.

Abstract: A device positionable in a borehole for monitoring relative mass displacements axially along the borehole between at least two spaced-apart anchor points, comprises at least two retrievable anchor members arranged in spaced-apart opposite relationship to define the at least two anchor points, the anchor members each having radially displaceable borehole wall contacting means and including mechanical means for radially outwardly displacing the borehole wall contacting means to engage the borehole wall and thereby fix the anchor member in the borehole against the wall thereof. A linear displacement sensing means is arranged between the anchor members, the displacement sensing means being connected to one of the anchor members and including an elongated axially movable sensor element, the sensor element being normally biased in a direction toward the other anchor member for contact engagement therewith.