There is provided an optical adder for accurately and additively specifying variable optical attenuation, which comprises a quarter wave plate disposed on an optical axis for changing an incident linearly polarized light beam emanating from a light source to a circularly polarized light beam; and one or more neutral density filter plates all disposed on the optical axis next to said quarter wave plate for attenuating the incident circularly polarized light beam respectively additively by a predetermined amount.
A variable bandwidth tunable optical filters comprised of two transparent optical substrates, upon each of which is deposited a linearly variable multilayer interference filter coating which varies in total thickness from end to end in a wedged fashion. This wedge imparts a corresponding variation of the center wavelength of the filter bandpass with respect to the linear position of the coated filter substrates. The variable bandpass tunable filter can be adjusted to a specific center wavelength by moving the filter pair together linearly through the incident beam. The bandwidth of the filter pair is maximized when the two filters are spectrally aligned, and is determined by the bandwidth of the individual filters. The variable bandwidth of the tunable filter can be adjusted by introducing a relative linear offset between the linearly variable filter pair.
An absorption spectroscopy device for determining the concentration of a gas (such as oxygen) in a sample cell includes a neutral density absorber or a quarter wave plate. Laser radiation from a laser diode passes through the neutral density absorber or the quarter wave plate, then passes through the sample cell, and then is incident upon a detector. In some embodiments, the laser diode is driven with a drive current having a stepped periodic waveform.
