Performance of photomultipliers in the context of laser-induced incandescence

Abstract

Photomultiplier tubes (PMTs) are widely used as detectors for laser-induced incandescence (LII), a diagnostics method for gas-borne particles that requires signal detection over a large dynamic range with nanosecond time resolution around the signal peak. Especially when more than one PMT is used (i.e., for pyrometric temperature measurements) even small deviations from the linear detector response can lead to significant errors. Reasons for non-linearity observed in other PMT measurement techniques are summarized and strategies to identify non-linear PMT operation in LII are outlined. To quantify the influence of the non-linear behavior, experiments at similar light levels as those encountered in LII measurements are carried out, and errors propagated in two-color pyrometry-derived temperatures are determined. As light sources, a calibrated broadband light source and light-emitting diodes (LEDs), centered at the bandpass filter wavelengths of the LII detectors, were used. The LEDs were operated in continuous and pulsed (<300 ns) mode, respectively, to simulate DC background radiation (e.g., from sooting flames) and similar pulsed signal traces as in typical LII measurements. A measured linearity deviation of up to 10% could bias the temperature determination by several hundred Kelvin. Guidelines are given for the design and the operation of LII setups, which allow users to identify and prevent errors.

Laser-induced incandescence for non-soot nanoparticles: recent trends and current challenges

“…Most often, the signal is measured at multiple wavelengths, either using photomultiplier tubes (PMTs) equipped with bandpass filters, or by dispersing the radiation and then imaging it onto a streak camera. Filtered PMTs provide high temporal resolution of the signal detection over a narrow spectral interval, and configurations using two or more (for enhanced dynamic range [38] or additional spectral information [39][40][41]) PMTs have been used to carry out LII on synthetic nanoparticles. On the other hand, gated spectrometers provide a spectrally resolved measurement at a particular instant, while spectrometer/ streak camera configurations can provide both spectrally and temporally resolved signals, albeit with a lower time resolution compared to PMTs.…”

A review on determining the refractive index function, thermal accommodation coefficient and evaporation temperature of light-absorbing nanoparticles suspended in the gas phase using the laser-induced incandescence

“…The authors of [39] stated that the peak temperature must be higher than the boiling temperature of the particle material and had supported their choice of wavelength dependence of E(m) by this statement (see discussion about Fe NP peak temperature in [39]). However, for NPs, it would be reasonable to suppose that the phase transition temperature is lower than that for the bulk material [119][120][121][122][123][124][125][126][127][128][129][130].…”

“…One of the additional uncertainties of the two-color temperature measurements has been pointed out in [120]. When the photo-multiplayer tube (PMT) was used for the pyrometric temperature measurements, even small deviations from the linear detector response can lead to significant errors.…”

“…A measured linearity deviation of up to 10% could bias the temperature determination by several hundred Kelvin. In [120], the guidelines are given for the design and the operation of LII set-ups, which allow users to identify and prevent errors.…”

Thermal Emission Spectroscopy of Single, Isolated Carbon Nanoparticles: Effects of Particle Size, Material, Charge, Excitation Wavelength, and Thermal History

“…Particle temperatures can be extracted by fitting emission spectra to a model that describes the emission intensity versus wavelength, typically using Planck’s law for ideal blackbody emission, together with a function, ε­(λ), that describes how the NP emissivity varies with wavelength. If the wavelength dependency of the emission is known, NP temperatures can also be extracted by two- or three-color thermometry, where calibrated intensities measured in two or three spectral regions are fit to an emission model to yield the temperature. , …”