Relative Quantum Efficiency as Measured at MIT CSR

  Results of the relative QE measurements described in Section 4.7.1 are presented in Table 4.26. The focal plane position of each flight device is listed in the table, along with the name of the reference device used during each measurement. The values in the table for the relative QE ratios are the fitted centroids of the Gaussian fits to the histograms of superpixel ratios. These values are our best estimates for the spatially averaged relative QE between the corresponding flight and reference detectors. Listed in parentheses are measurements of the spatial variation (RMS) in efficiency across each chip, obtained by computing the standard deviation of the 1024 superpixel ratios in each measurement. Note that the relative QE ratio listed for w140c4r at 0.525 keV is referenced to w134c4r, a BI chip. No measurement relative to w103c4 was made at this energy because of time constraints.

In Table 4.27 we have used the values given in Table 4.26 to compute relative QE ratios referenced to w190c3 for each flight device. The results are plotted in Figure 4.65. Most of the relative efficiency points lie within 5% of unity and all but two of the points lie within 10%, indicating that at each energy the absolute efficiencies of the eight FI devices are nearly identical. We have computed the mean relative efficiency and the maximum absolute deviation from the mean for each CCD type as a function of energy (see Table 4.28). The largest absolute deviations from the mean ($\sim$10-18%) in the FI devices are at 0.525 and 0.677 keV. These are caused by the high relative efficiency of w182c4r at these energies, which in turn is due to that detector's relatively thin oxide layer. From the RMS variations listed in Table 4.27 it can be seen that spatial variations in efficiency across the FI devices are low ($\sim$2-4%). Thus, we find that the detection efficiencies of the FI devices are highly uniform within each chip and between chips.

The BI CCDs are about three times more efficient than the FI devices at low energies (< 1 keV), but are less efficient than the FI devices at high energies. Spatial variations in efficiency across the BI devices are larger ($\sim$5-8%) than in the FI devices. However, differences in absolute efficiencies between the BI devices are comparable to those for the FI devices.

 

Device Position Mean (RMS) Relative Efficiency vs. Energy (keV) Reference Device

0.525 0.677 1.740 2.015 4.509 5.894 8.040

O F Si P Ti Fe55 Cu

w203c4r I0 0.973 0.994 0.998 0.986 0.996 0.979 0.936 w190c3

(0.019) (0.020) (0.025) (0.024) (0.026) (0.026) (0.025)

w193c2 I1 0.885 0.769 0.963 0.966 1.005 1.033 1.087 w103c4

(0.016) (0.017) (0.027) (0.028) (0.026) (0.030) (0.038)

w158c4r I2 0.914 0.805 0.974 0.980 1.006 1.030 1.096 w103c4

(0.016) (0.017) (0.026) (0.026) (0.024) (0.028) (0.032)

w215c2r I3 1.000 1.016 0.998 0.991 0.982 0.986 0.932 w190c3

(0.019) (0.019) (0.019) (0.018) (0.018) (0.019) (0.019)

w168c4r S0 1.058 1.090 1.006 1.015 0.999 0.974 0.919 w190c3

(0.027) (0.024) (0.021) (0.020) (0.022) (0.021) (0.022)

w182c4r S2 1.009 0.965 0.987 1.017 1.015 1.068 1.211 w103c4

(0.021) (0.024) (0.021) (0.023) (0.023) (0.024) (0.032)

w457c4 S4 1.022 1.078 1.007 1.019 1.001 1.000 1.003 w190c3

(0.017) (0.027) (0.027) (0.028) (0.026) (0.026) (0.027)

w201c3r S5 1.006 1.035 1.001 0.993 1.001 1.001 1.008 w190c3

(0.019) (0.021) (0.022) (0.021) (0.022) (0.024) (0.026)

w140c4r S1 1.012 1.079 w134c4r

(0.022) (0.036)

2.499 1.016 1.456 0.944 0.766 0.634 w103c4

(0.089) (0.044) (0.082) (0.084) (0.060) (0.047)

w134c4r S3 3.408 2.943 1.098 1.542 1.014 0.882 0.745 w203c2

(0.066) (0.157) (0.023) (0.038) (0.039) (0.039) (0.043)

w190c3 Ref. 0.891 0.768 0.982 0.949 1.009 1.058 1.211 w103c4

(0.020) (0.017) (0.028) (0.027) (0.027) (0.031) (0.035)

w203c2 Ref. 0.873 0.787 0.960 0.964 1.004 1.009 1.041 w103c4

(0.017) (0.017) (0.024) (0.024) (0.025) (0.027) (0.031)

 

 

Device Position Mean (RMS) Relative Efficiency vs. Energy (keV)

0.525 0.677 1.740 2.015 4.509 5.894 8.040

O F Si P Ti Fe55 Cu

w203c4r I0 0.973 0.994 0.998 0.986 0.996 0.979 0.936

(0.019) (0.020) (0.025) (0.024) (0.026) (0.026) (0.025)

w193c2 I1 0.993 1.001 0.981 1.018 0.996 0.976 0.898

(0.029) (0.031) (0.039) (0.041) (0.037) (0.040) (0.041)

w158c4r I2 1.026 1.048 0.992 1.033 0.997 0.974 0.905

(0.029) (0.032) (0.039) (0.040) (0.036) (0.039) (0.037)

w215c2r I3 1.000 1.016 0.998 0.991 0.982 0.986 0.932

(0.019) (0.019) (0.019) (0.018) (0.018) (0.019) (0.019)

w168c4r S0 1.058 1.090 1.006 1.015 0.999 0.974 0.919

(0.027) (0.024) (0.021) (0.020) (0.022) (0.021) (0.022)

w182c4r S2 1.132 1.257 1.005 1.072 1.006 1.009 1.000

(0.035) (0.042) (0.036) (0.039) (0.035) (0.037) (0.039)

w457c4 S4 1.022 1.078 1.007 1.019 1.001 1.000 1.003

(0.017) (0.027) (0.027) (0.028) (0.026) (0.026) (0.027)

w201c3r S5 1.006 1.035 1.001 0.993 1.001 1.001 1.008

(0.019) (0.021) (0.022) (0.021) (0.022) (0.024) (0.026)

w140c4r S1 3.379 3.254 1.035 1.534 0.936 0.724 0.524

(0.141) (0.136) (0.054) (0.097) (0.087) (0.061) (0.042)

w134c4r S3 3.339 3.016 1.073 1.566 1.009 0.841 0.640

(0.118) (0.186) (0.047) (0.071) (0.054) (0.050) (0.046)

 

 

Device Mean (Max. Abs. Dev.) Relative Efficiency vs. Energy (keV)

0.525 0.677 1.740 2.015 4.509 5.894 8.040

O F Si P Ti Fe55 Cu

FI 1.026 1.065 0.998 1.016 0.997 0.987 0.950

(0.106) (0.192) (0.018) (0.056) (0.015) (0.022) (0.058)

BI 3.359 3.135 1.054 1.550 0.972 0.782 0.582

(0.020) (0.119) (0.019) (0.016) (0.036) (0.058) (0.058)

 

  

Figure 4.65: Relative detection efficiencies of flight CCDs as a function of energy--referenced to w190c3.