Etendue or throughput is a property of light in an optical system. Most spectrometer designs require a slit to produce high-resolution spectroscopy results. This slit is required due to the etendue of the solid angle area that can be accommodated by the instrument. This limits the throughput of the instrument or the amount of light that can be passed through the device. This can result in more than 95 % of the light being thrown away by the instrument making it difficult to obtain accurate measurements of the target substance. ISI’s high throughput spectrometer and Raman spectrometer does not require a slit and can accept all the light from a 1 mm diameter 0.22 NA optical fibre, greatly increasing sensitivity.