J. Eur. Opt. Society-Rapid Publ. 22, 52( 2026) 513
( a)( b)( c)
Fig. 2. Waterfall plot and surface plot( b) for the flash extinction from one xenon arc lamp, with one spectrum every 221 ls; the grey curve in( a) displays the ASTMG173 1000 W / m2 reference spectrum; the black arrow indicates the direction of extinction, i. e. from red to blue curves;( c) time series for selected wavelengths from data in( a) and( b), normalized over each curve’ s maximum.
3 Results and discussion
3.1 Characterization of flash extinction
Figure 2a depicts a typical flash from one lamp at a given supply voltage, compared to the ASTMG173 1000 W / m 2 reference spectrum, that the simulator tries to emulate with a ± 25 % maximum mismatch( class A). Each spectrum is formed by a broad blackbody radiation that peaks around 570 nm and quickly decreases to 50 % after 2.5 ms, superimposed with narrow Xe discharge spectral lines( e. g., 764 and 822 nm) that decrease more slowly, and never turn off completely during the 6 ms window. Since different wavelengths exhibit different dynamics, the temporal variation should be considered at each wavelength, such as those visible in the plots in Figures 2b – 2c.
3.2 Impact of supply voltage on lamp’ s flash
Supply voltage is varied to adjust the simulated irradiance until the 1-sun short-circuit current density( J sc) ofthe DUT matches that of a calibrated reference cell, regardless of the differences in spectral response of the two devices [ 1 ], which is taken into account by the spectral mismatch factor( SMM, or M). When adjusting the supply voltage, one expects the whole spectrum to vary coherently, with every wavelength showing the same increase / decrease with increasing / decreasing voltage. If this was the case, spectral irradiance at any wavelength would increase linearly with supply voltage, integrated irradiance would increase linearly with supply voltage, and measured J sc would increase linearly as well.
Results in Figure 3a, however, report that this occurs only for the blackbody radiation( around 600 nm), and that the wavelengths corresponding to the Xe lines( e. g., 764 and 823 nm) exhibit a slower increase with voltage, marked by the dips visible in Figure 3b. Irradiance does not increase coherently with supply voltage, as visible in Figure 3c, but lines and 764 and 823 nm exhibit slower increases with voltage. This non-ideal behaviour might introduce measurement artifacts, as spectra with higher supply voltage lacks some IR spectral components.
The effect can thus be estimated through the top / middle Spectral Mismatch Ratio plotted in Figure 3d, defined
R as SMR top = mid ¼ R
E mistop ðkÞdk E mismid ðkÞdk
R R
E refmid ðkÞdk
E reftop k
, beingE ð k Þ the mea- ð Þdk
sured / reference spectral irradiance in W / m 2 nm for the In- GaP-top( 350 – 650 nm) or InGaAs-middle( 650 – 950 nm) range. Consistent with results in Figure 2, and with results reported in [ 2 ], the SMR top = mid within the first 5 ms increases with applied voltage and decreases with time as the spectra become richer with IR, since these components decrease faster during the flash extinction.
3.3 Impact of supply voltage on measured I – V curves
Results reported in Section 3.2 suggest that the spectrum at one supply voltage( e. g. 650 V) does not increase coherently with voltage, but discharge at higher voltages( e. g. 800 V) lack of some spectral components, such as 467, 764, 823 nm, etc. Varying supply voltage without evaluation of its impact might lead to an underestimation of the simulator’ s irradiance and to an underestimation of the measured J sc.
In order to prove this claim, we measured the I-V curves of three different devices, each sensitive to a different spectral range, thus each including a different number of the dips shown in Figure 3b. We expect the more dips are included in the DUT’ s range, the stronger underestimation of the J sc.
For this purpose, Figure 4 shows, for each device, the J sc at different supply voltage( 650, 700, 750, 800 V), normalized over its value at 650 V. Each data point is the result of 5 consecutive measurements.
4 Discussion
Results in Section 3.1 reveal that a typical xenon lamp’ s intensity does not decrease coherently during its extinction, but it’ s formed by spectral lines that decrease far more slowly than others. This dynamics can be considered coherent enough during the first 1 ms of the extinction, where voltage – current sweeps are carried out, as shown in the SMR reported in Figure 3d. This assumption was possible thanks to speed of the spectrometer that allowed to characterize the flash dynamics with good temporal resolution.