Left: SOLAR/SOLSPEC optical path of one spectral channel (double-monochromator). The sunlight passes through the entranceslit of the double monochromator and goes in the plane of an intermediate slit through a first monochromator grating and a first mirror. Then, the sunlight goes in the plane of the exit slit through a second mirror and a second monochromator grating identical to the first. Diffraction gratings are used to disperse light (spatial separation of various wavelengths). The wavelength depends on the rotation angle of the grating. The two grating arrangements share the same axis ofrotation. This guarantees short scan times at high stability and wavelength accuracy. This design is used in applicationsin which scattered light must be kept to a minimum. Right: general view of the SOLAR/SOLSPEC flight model with its three channels during integration. SOLAR/SOLSPEC had 3 double monochromators (UV, VIS and IR).