Multi-channel Smartphone Spectrometer Using Combined Diffraction Orders

A robust multi-channel smartphone spectrometer exploiting multi-order diffraction imaging on a smartphone camera is reported. The instrument utilizes a thin film diffractive element generating multiple orders of diffracted light from a broadband visible source (white LED, = 400 ~ 700 nm). The smartphone's CMOS camera captures all the diffraction orders simultaneously, producing a 2D image. Each of these diffraction orders can be utilized as a single optical channel for dedicated samples enabling simultaneous multiple sample analysis. The wavelength distribution along the diffraction direction produces a tunable spectral resolution of ~ 1.6 to 3.0 nm/pixel over the bandwidth of = 300 nm. A customized app processes each diffraction image into spectra. 3D printing is used to create the entire instrument prototype. As an initial demonstration, simultaneous absorption measurements of reference and sample cells using the first diffraction orders (m = +1 and -1) is shown. Absorption spectra for a laser dye (Rhodamine B) and a pH-responsive buffer (bromothymol blue) are measured. This offers a low cost (< 30) portable instrument layout comparable to conventional double beam benchtop instruments in performance but more rugged for field use.