The latest Optics & Photonics News has an overview article on ‘Freeform Optics’. These are defined as optics which lack translational or rotational symmetry, and which therefore have historically been difficult to fabricate. As simple example is progressive eyeglasses (which I wear…). The article quotes a set of spectrometer designs that achieved a threefold increase in spectral bandwidth and a fivefold increase in compactness, relative to non-freeform designs.
This isn’t all new --- a 2009 paper used freeform optics in a Czerny-Turner spectrometer to suppress astigmatism. And Czerny-Turner designs are used in a large number of portable Raman spectrometers.
So will freeform optics be the next step in size and weight reduction for portable spectrometers? Remember, if you are carrying a lot of gear (spectrometers included) then ounces equals pounds, and pounds equals pain.