Abstract: An optical module includes a micro spectrometer. The micro spectrometer includes an optical crystal, a lens, and a photosensitive assembly. The optical crystal is configured to receive detection light and covert the detection light into interference light. The optical crystal is surrounded by a sleeve, the sleeve configured to fix a position of the optical crystal. The lens is configured for receiving the interference light and focusing the interference light. The photosensitive assembly is configured for imaging the interference light into an interference image. The optical module further comprises a controller. The controller is electrically connected to the photosensitive assembly, and the controller is used to convert the interference image into light wavelength signals and light intensity signals.

Abstract: A wavelength-swept light source is configured to generate light to be measured that is wavelength-swept coherent light with a wavelength periodically changed. The light to be measured is separated into a measurement section and a reference section that have different optical path lengths, and is then coupled in an interference section to generate interfering light. An analyzer performs a Fourier transform of interference signals of the interfering light, and acquires an actual measured noise floor value for each of the optical path length differences based on a point spread function. An estimated coherence time is determined so that an actual measured amplitude value of the noise floor value and a calculated amplitude value coincide with each other. Linewidth of the light emitted from the coherent light source is measured based on the estimated coherence time.

Abstract: A radiation measurement system (200) comprising an optical apparatus (205) configured to receive a radiation beam (210) and change an intensity distribution of the radiation beam to output a conditioned radiation beam (215), and a spectrometer (220) operable to receive the conditioned radiation beam and determine spectral content of the conditioned radiation beam. The radiation measurement system may form part of a lithographic apparatus.