Most spectrometer designs currently available today require a slit to produce high resolution spectroscopy results. This slit is required due to the etendue or the solid angle area product 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 slit can result in more than 95 % of the light being thrown away by the instrument, however as this fact is a constant this is not taken into account in the final instrument transmission specifications. ISI 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.