An optical system for measuring an optical density of a sample in which homogeneity of light employed for measuring the density thereof is secured by including optical information upon a light source uniformly inside a measurement space about an optical axis therein even if the fluctuation occur in the light source in the system. A beam of light emitted from the light source and then focused on an interference filter is transformed into a parallel light through a collimator lens, and the parallel light is then split into two parallel pencils of light by an optical mask. The parallel light uniformly includes the optical information upon the light source. A reference cell is placed in a first split parallel pencil of light, and a sample cell is placed in a second split parallel pencil of light. The lights that have passed through the two cells are focused on an optical receiver by a focusing lens.

A method capable of acquiring data at a high speed while holding proper precision during measurement with an infrared imaging apparatus uses an FTIR device of a continuous scan type for detecting a signal by a multi-element detector. A method which acquires data from a multi-element detector in an infrared imaging apparatus. The method involves starting to scan an element of the said multi-element detector synchronously with a sampling signal based on a reference signal of an interferometer, and scanning the element at a higher frequency than a sampling frequency of the sampling signal. The method further involves completing the scanning of all the elements before a next sampling signal to the sampling signal starting the element scanning is generated, and repeating a series of operations every time the sampling signal is generated.

A metrology system includes a sample holder and a backside reflective element. The backside reflective element causes light that is transmitted through the sample to be reflected and transmitted a second time, in the opposite direction, through the sample. A variable collection range can be adjusted to place the sample, the reflective element or both within the collection range. The collection range is the range of focused light that will be detected. The system can be controlled to move one or both of the sample and the reflective element in or out of the collection range or to alter the optics to adjust the collection range so that one or both of the sample and reflective element are in the collection range. Thus, the metrology system can be configured to operate in reflectance mode, transmittance mode or a mixed reflectance/transmittance mode.

A Fourier-transform (FT) infrared (IR) spectrometer includes a Michelson interferometer without an IR beam compensator. An input IR beam is directed through a substrate and a beamsplitter attached to the substrate for support, with the input IR beam divided by the beamsplitter into a first beam portion incident upon a fixed retroreflector and a second beam portion incident upon a movable retroreflector. The first and second beam portions are then recombined to provide an uncompensated output IR beam with an interference pattern which is directed onto a sample to provide an uncompensated interferogram. The uncompensated interferogram is converted from a time domain to a frequency domain via a Fourier-transform to provide a complex intermediate spectrum, followed by a calculation of a corrected phase angle in terms of wavenumber arising from the substrate's optical thickness. The complex intermediate spectrum is then rotated by a negative of the corrected phase angle. An inverse Fourier-transform is used to form a corrected real compensated intermediate interferogram. The corrected real compensated intermediate interferogram is then Fourier-transformed into a spectrum using a conventional approach to remove asymmetric noise and correct for small phase errors.

Methods and devices are provided for determining the presence and/or concentration of at least one analyte in a sample of low transmissivity. In the subject methods, a forward beam and a backward beam are produced by or introduced into an interferometer from at least one infrared radiation source. The forward beam is passed into the sample and then collected to produce a sample beam while the backward beam is passed into a reference and then collected to provide a reference beam. The sample and reference beams are recombined either optically into a null beam which is detected at a single detector or electronically nulled after detection on two separate detectors. The presence, and often amount, of at least one analyte in the sample is then derived from the detected null beam. Also provided are devices for practicing the above methods. The subject methods and devices are suitable for use in a variety of different applications, including the detection of the presence, and amount, of one or more blood analytes in a physiological sample, such as blood, tissue or derivatives thereof.