A fast multispectral light synthesiser based on LEDs and a diffraction grating

Abstract

Optical experiments often require fast-switching light sources with adjustable bandwidths and intensities. We constructed a wavelength combiner based on a reflective planar diffraction grating and light emitting diodes with emission peaks from 350 to 630 nm that were positioned at the angles corresponding to the first diffraction order of the reversed beam. The combined output beam was launched into a fibre. The spacing between 22 equally wide spectral bands was about 15 nm. The time resolution of the pulse-width modulation drivers was 1 ms. The source was validated with a fast intracellular measurement of the spectral sensitivity of blowfly photoreceptors. In hyperspectral imaging of Xenopus skin circulation, the wavelength resolution was adequate to resolve haemoglobin absorption spectra. The device contains no moving parts, has low stray light and is intrinsically capable of multi-band output. Possible applications include visual physiology, biomedical optics, microscopy and spectroscopy.

The Fly Sensitizing Pigment Enhances UV Spectral Sensitivity While Preventing Polarization-Induced Artifacts

“…where α is the e-vector angle, A the amplitude, and ϕ the phase shift and C the offset. PS was calculated as PS = S max / S min ; for details, see Belušič et al (2016 , 2017 ).…”

“…A rhabdomere was sliced into 1 μm cylindrical segments with uniform microvillar orientation at angle ϕ m . Rhodopsin absorption spectra were either calculated in 5 nm intervals in the range 300–600 nm , using a rhodopsin template ( Stavenga et al, 1993 ), taken from the published data (R8y; Hardie, 1985 ) or from own measurements (sensitizing pigment; Belušič et al, 2016 ). The dichroic ratio Δ was either constant, Δ = 10, or in the presence of the sensitizing pigment varied as a function of wavelength, λ : Δ λ = 1 (300 < λ < 370 nm), 1 < Δ λ < 10 (sigmoidally increasing from 1 to 10 for 370 < λ < 400 nm), Δ λ = 10 ( λ > 400 nm).…”

Chromatic information processing in the first optic ganglion of the butterfly Papilio xuthus

“…We also used an LED (light-emitting diode) array device with 21 narrow-band LEDs with peak wavelengths of 365,375,390,403,422,435,451,471,495,514,525,540,560,577,590,595,620,630,657,673, and 686 nm to produce light of arbitrary spectral content (Belušič et al 2016). The quantum flux was controlled using 12-bit pulse width modulation at 1 kHz and a set of ND filters.…”

A novel setup for simultaneous two-photon functional imaging and precise spectral and spatial visual stimulation in Drosophila

“…Very little is known about how outputs of different photoreceptors might be combined by colour-encoding circuits, highlighting the need for high resolution spectral stimulus capabilities. Our system uses narrow bands of monochromatic light well suited to our investigation into spectral response properties, but it is entirely possible to modify the light source to produce multispectral light using a system such as the LED-based monochromator 40 . Methods commonly employed in mammalian vision research, such as the sophisticated combination of multispectral light to effectively target only one class of photoreceptors 46 , are limited in invertebrates.…”