The present invention concerns an improved polarizer assembly for a spectrofluorometer and, more particularly, a novel polarizer assembly in which the input polarizer and the output polarizer are each modular and have self-contained motor drives.
Known in the art is a spectrofluorometer which includes an excitation monochromator which directs a light beam from a suitable light source through an excitation or input polarizer to a sample, from the sample through an emission or output polarizer and a depolarizer to an emission monochromator and to a detector. In polarization measurements, a fluorescent solution is excited by the beam of light whose electric vector is polarized vertically with the excitation polarizer. Since the electric and magnetic vector components of the light beam are always perpendicular to each other and have equivalent magnitudes, only the electric vector is specified. The vertically polarized light will excite only those sample molecules with vectors that are not perpendicular to the direction of polarization. The intensity of the two linearly polarized components of the fluorescent light emitted by the sample is measured by orienting the emission polarizer so as to transmit one component and then the other.
Thus in polarization measurements, the polarization of the generated light, which is emitted from the sample when polarized light is directed into the sample, may be indicative of the size of the particles in the sample. Prior art spectrofluorometers typically include an excitation (input) polarizer and an emission (output) polarizer with each of the polarizers comprising a polarizing filter that is rotatable between a vertical position and a horizontal position. In one application, a depolarizer is associated with the emission polarizer for depolarizing the emitted light from the sample which is then passed to a detector, such as a photomultiplier tube. In other applications, the depolarizer replaces either the emission or excitation polarizer.
Prior art polarizer assemblies were not constructed on a fully modular basis and did not include polarizer modules that were easily rearranged to perform alternate functions. Prior art motorized polarizers typically had the motor mounted to a base and a mechanical drive was coupled to each of the polarizers, thereby requiring that the drive be disconnected in order to remove the respective polarizer. Further, in prior art polarizer systems, in order to achieve 90.degree. rotation in some instances the motor would be energized for a time duration sufficient to ensure that the travel had been completed. In other instances, a switch closure would be provided in order to deenergize the motor. Prior art polarizer assemblies which were not motorized would typically require the operator manually to move the polarizer 90.degree. from a vertical position to a horizontal position.
It is an object of the present invention to provide a modular polarizer assembly in which the polarizers can be located in alternate positions on a mounting base for various functions.
Another object of the present invention is to provide modular polarizers which each have self-contained motor assemblies.
A further object of the present invention is to provide a system in which the polarizer filters of a polarizer assembly are motor driven with means for ensuring that the filters rotate exactly 90.degree. as required.
Other objects and advantages of the present invention will become apparent as the description proceeds.