Open hardware microsecond dispersive transient absorption spectrometer for linear optical response

Christopher D M Hutchison,Susan Parker,Jasper J Van Thor,Volha Chukhutsina

doi:10.1007/s43630-021-00127-6

Christopher D M Hutchison, Susan Parker + Show 2 more

Open Access

https://doi.org/10.1007/s43630-021-00127-6

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Abstract

An open hardware design and implementation for a transient absorption spectrometer are presented that has microsecond time resolution and measures full difference spectra in the visible spectral region from 380 to 750 nm. The instrument has been designed to allow transient absorption spectroscopy measurements of either low or high quantum yield processes by combining intense sub-microsecond excitation flashes using a xenon lamp together with stroboscopic non-actinic white light probing using LED sources driven under high pulsed current from a capacitor bank. The instrument is sensitive to resolve 0.15 mOD flash-induced differences within 1000 measurements at 20 Hz repetition rate using an inexpensive CCD sensor with 200 μm pixel dimension, 40 K electrons full well capacity and a dynamic range of 1800. The excitation flash has 230 ns pulse duration and the 2 mJ flash energy allows spectral filtering while retaining high power density with focussing to generate mOD signals in the 10–4–10–1 ΔOD range. We present the full electronics design and construction of the flash and probe sources, the optics as well as the timing electronics and CCD spectrometer operation and modification for internal signal referencing. The performance characterisation and example measurements are demonstrated using microsecond TAS of Congo red dye, as an example of a low quantum yield photoreaction at 2% with up to 78% of molecules excited. The instrument is fully open hardware and combines inexpensive selection of commercial components, optics and electronics and allows linear response measurements of photoinduced reactions for the purpose of accurate global analysis of chemical dynamics.Graphical abstract

Highlights

Pushing the limits of flash photolysis to unravel thesecrets of biological electron and proton transfer—a topical issue inhonour of Klaus Brettel.The technique of Transient Absorption Spectroscopy (TAS) is well established, from the early work of George Porter and others who used flash sources for excitation and probing of chemical reactions [1,2,3,4,5] (Nobel Prize in Chemistry 1967)
The construction includes a separate fully enclosed and shuttered “laser box” which allows high power Continuous Wave (CW) or Transistor–Transistor Logic (TTL) triggered laser to be used in conjunction with the transient absorption setup
The estimated quantum yield for this reaction under our conditions is ~ 2%, which demonstrates the device’s ability to measure low quantum yield dynamics

Summary

Introduction

Pushing the limits of flash photolysis to unravel thesecrets of biological electron and proton transfer—a topical issue inhonour of Klaus Brettel.The technique of Transient Absorption Spectroscopy (TAS) is well established, from the early work of George Porter and others who used flash sources for excitation and probing of chemical reactions [1,2,3,4,5] (Nobel Prize in Chemistry 1967). Recording time-resolved spectral information is powerful to separate heterogeneous reactions and to resolve multi-phasic decay and complex reaction pathways For such analysis, the TAS data is analysed using Singular Value Decomposition (SVD), global fitting and target analysis techniques [8]. The choice to record full spectra rather than single wavelength traces has implications with regard to the reduced sensitivity of the difference absorption that can be detected. It is, important that the instrumentation combines both high enough sensitivity (typically ~ 0.15 mOD differences) together with large enough excitation power density to generate a sufficient dynamic range in the photoinduced difference measurements to allow the SVD and global analysis

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