GALIUS: an ultrafast imaging spectrograph for the study of lightning

Abstract

We present the main parameters, design features and optical characterization of the GrAnada LIghtning Ultrafast Spectrograph (GALIUS): a portable, ground-based spectrographic system intended for the analysis of the spectroscopic signature of lightning. It has been designed to measure the spectra of the light emitted from natural and triggered lightning and artificial electrostatic discharges at recording speeds up to 2.1 Mfps. It includes a set of four interchangeable grisms covering different spectral ranges (from 375 nm to 854.5 nm) with spectral resolutions from 0.29 to 0.76 nm. A set of ten collector lenses allows to record the spectrum of electrostatic discharges and lightning in different scenarios.

Submicrosecond Spectroscopy of Lightning‐Like Discharges: Exploring New Time Regimes

“…The investigations presented here have been carried out with an very fast (2.1 Mfps or 0.476 μs per frame with an exposure time of 160 ns) and high spectral resolution (between 0.29 and 0.75 nm depending on the grating used) spectrograph named GrAnada LIghtning Ultrafast Spectrograph (GALIUS) recently developed by the IAA‐CSIC atmospheric electricity group (Passas et al., 2019). A total of 22 possible configurations can be set up with GALIUS, combining 10 interchangeable collector lenses (with focal lengths ranging from 25 to 200 mm) with two different collimator lenses (105 mm with F#4.5 and 50 mm with F#1.2 focal lengths for, respectively, the UV and visible‐NIR ranges) and four interchangeable volume‐phase holographic (VPH) grisms for spectral ranges from the near UV (380 nm) to the near IR (850 nm) (Passas et al., 2019).…”

“…GALIUS can operate in slit or slitless mode and incorporates a very high speed Photron FASTCAM SAZ camera with a high light‐sensitive image CMOS sensor (monochrome ISO 50000) of 1,024 × 1,024 of 20 μm square pixels, with 12 bit ADC pixel depth. Finally, GALIUS incorporates a fast photodiode‐based photometer for triggering when a threshold of photons is reached (Passas et al., 2019).…”

High‐Speed Spectroscopy of Lightning‐Like Discharges: Evidence of Molecular Optical Emissions

“…GALIUS can be set up with a total of 22 configurations made of combinations of 10 collector lenses (focus lengths ranging from 25 to 200 mm), two different collimator lenses in the UV and visible‐NIR range (105 mm with F#4.5 and 50 mm with F#1.2) and four interchangeable volume‐phase holographic (VPH) grisms for spectral ranges from the near ultraviolet (380 nm) to the near infrared (805 nm) and high‐spectral resolution (0.29–0.75 nm depending on the grating used). More details about GALIUS and its configurations can be found elsewhere (Kieu et al., 2020; Passas et al., 2019).…”

“…They used an ultrafast spectrograph named GrAnada Lightning Ultrafast Spectrograph (GALIUS) Passas et al. (2019). These lightning‐like discharges were recorded at 2,100,000 fps with time resolution of 0.416 μ s (160 ns exposure time) within a reduced spectral range (645–665 nm).…”

“…Recently, Kieu et al (2020) have explored spectral features of meter long lightning-like discharges in the submicrosecond time regime. They used an ultrafast spectrograph named GrAnada Lightning Ultrafast Spectrograph (GALIUS) Passas et al (2019). These lightning-like discharges were recorded at 2,100,000 fps with time resolution of 0.416 μs (160 ns exposure time) within a reduced spectral range (645-665 nm).…”