Compact Gas Analysis Arrangement with Short Optical Path

The optical path is segmented into multiple passes through the gas sample using mirrors or beam steering optics. The light traverses the measuring distance multiple times (e.g., 10-100 passes), effectively increasing the path length and sensitivity without increasing the physical device dimensions. This allows achieving high sensitivity in compact configurations.

Instead of extending the measuring distance in one dimension, the patent uses multi-pass optical configurations that fold the light path through the gas sample multiple times within a compact volume. This transforms a one-dimensional length requirement into a multi-dimensional optical path arrangement, achieving extended effective path length without proportional increase in device footprint.

The system employs a broadband light source that emits across multiple wavelengths simultaneously. By using a narrow slit to select specific wavelength bands and combining this with multi-pass optical paths, the system accumulates sufficient light intensity at the detector while maintaining spectral resolution. The periodic emission of broadband radiation ensures continuous availability of photons across the spectral range of interest.

The optical system combines multiple components with complementary functions: broadband light source, wavelength-selective filters or monochromators, multi-pass mirrors, and sensitive detectors. This composite optical arrangement ensures that sufficient light intensity is delivered to the detector while maintaining the spectral selectivity provided by the narrow slit, resolving the contradiction between intensity and accuracy.

The patent extracts or removes the harmful indirect radiation heat from the optical path by using narrow slits and aperture restrictions that allow only direct ballistic photons to reach the detector. Thermal radiation, which follows different propagation paths and is more likely to be scattered or reflected, is excluded by the geometric constraints of the narrow optical path. This separation of desired signal (direct radiation) from harmful interference (indirect thermal radiation) improves measurement accuracy.

The system converts the challenge of thermal radiation into a benefit by using the narrow slit geometry to create a natural spatial filter. The restricted optical path length and geometry inherently favor direct photons while excluding scattered thermal radiation, effectively using the same optical constraints that provide spectral resolution to also provide thermal noise rejection. This turns a potential limitation into a dual-function feature.