Progressive report 6
Test of Superlogics and verification of cut off wavelengths of long pass
filters
1. Test of superlogics and unit of output signal of photodiode
I measured output signal of photodiode with superlogics and verify exact unit of output
signal from photodiode. I directly measured output signal of photodiode with
oscilloscope and then read output of photodiode with superlogics in IDL again. Below
two figures show the setup of devices for measurement.
<Figure 1. Setup of devices to measure the output signal from photodiode>
I made a measurement from 4 different cases; saturation, intermediate light on, low gain
and high gain, respectively. To measure the output signal with low and high gain, I
switch up and down during the exposure. Below tables show the measurement of
saturation case and intermediate light on case.
Type of
Measurement with oscilloscope
Measurement with Superlogics
photodiode
(Volts)
(Volts)
Low gain
High gain
Low gain
High gain
SN1(Si)
+13.1 ~13.6
+13.1 ~13.6
10.0000
10.0000
SN1(Ge)
0.006 ~ 0.016
-0.013 ~ 0.006
0.02000
0.17500
SN2(Si)
+13.0 ~ 13.8
+13.0 ~ 13.8
10.0000
10.0000
SN2(Ge)
0.028 ~ 0.153
-0.006 ~ 0.022
0.00400
0.05100
<Table 1. Comparison of saturation level between Oscilloscope and super logics>
Type of
photodiode
Measurement with Superlogics
(Volts)
Low gain
High gain
SN1(Si)
0.251000
2.42900
SN1(Ge)
-0.00600000
-0.0490000
SN2(Si)
0.286000
2.81100
SN2(Ge)
-0.0170000
-0.152000
<Table 2. Measurement of output with superlogics in the intermediate light on>
As you can see above tables, the unit of output through the superlogics is Volts. In
addition, real saturation level of photodiode is above 13V but superlogics can only read
up to 10V. So we should keep in mind our superlogics can’t measure above 10V.
Below figures show well our superlogics can read and give exactly same level of input
signal only below 10V.
I generated 5 different square wave as for input signals (+/- 0.01V, +/-0.1V, +/-1V, +/5V, +/-10V) using a function generator and then read them with superlogics in IDL.
Distortion shown on the plot is caused by impedance matching problem of BNC cable.
But we can ignore it for simple comparison of input and output signal.
<Figure2. Output signals with superlogics. The output is exactly same of input signal
created by function generator>
I used same way to check the different channels (Ch2, Ch3, and Ch4) of superlogics.
Below figures show the measurement using different channels of super logics. I feed the
square wave (+/- 100mV) generated by function generator into the ch2, ch3, ch4 of
superlogics. It shows all channels are working properly. 4 channels (ch0~ch3) used for
measurement will be connected to two photodiodes to get the signals from them.
<Figure 3. output signals from different channels, ch2, ch3, ch4>
Based on the above results, our all devices such as photodiode, superlogics and designed
bud box are working well and the output unit of photodiode through the superlogics is
Voltage. The saturation level of photodiode is around13.6V but our superlogics can
measure only up to 10V. In addition, high gain setting multiply data by 9.7 for the Si
channel of photodiode1 (SN: 60727-1) and 9.8 for the Si channel of photodiode2 (SN:
60727-2), respectively. For high gain setting of Ge of photodiode1 (SN: 60727-1) and
photodiode2 (SN: 60727-2) multiply 8.17 and 8.94, respectively.
2. Verification of cut off wavelength of long pass filters
Our monochromator is installed 4 long pass filters with different cut-off wavelengths.
Below Table shows currently installed long pass filters and their cut-off wavelengths.
Position number
1
2
3
4
5
6
Cut-off wavelength (nm)
Open
320
590
655
715
Blocked
We measured output voltage to verify cut off wavelengths of long pass filters. Below
tablae and figure 4 shows cut off wavelength and output signal using each filter. I
measured the output signal with superlogics in some specific wavelengths (10 or more
specific wavelengths). Due to the small number of data number, the plot looks discrete.
filter2
Wave(nm)
295
300
305
310
315
316
317
318
319
320
322
325
327
330
335
340
350
360
365
370
380
Output(V
)
0.387
0.387
0.388
0.43
0.619
0.681
0.751
0.83
0.92
1.015
1.234
1.621
1.895
2.354
3.242
4.279
6.4
8.119
9.019
10
10
filter3
Wave(nm
)
540
550
560
570
580
585
586
587
590
600
Output(V
)
0.055
0.063
0.094
0.368
3.128
8.101
9.556
10
10
10
filter4
Wave(nm
)
615
625
635
645
655
660
663
665
666
667
670
680
Output(V
)
0.043
0.044
0.047
0.059
0.332
1.601
3.848
6.478
8.27
10
10
10
filter5
Wave(nm
)
665
675
685
695
705
707
710
711
712
715
725
Output(V
)
0.05
0.07
0.146
0.569
3.396
4.803
7.811
9.121
10
10
10
(a) filter2 (320nm cut off)
(b) filter3 (590nm cut off)
(c) filter4 (665nm cut off)
(d) filter5 (715nm cut off)
<Figure 4. Measurement of output voltage with long pass filters. Dotted vertical lines in
each panel represent cut off wavelength, respectively>
Fig 5 is same of figure 4. It is created with smaller readout step than figure 4. All plots
look smoother than figure 4 but output values are not exactly matched to the wavelengths
because it is continuously varying due to the setup of scan rate.
(a) filter2 (320nm cut off)
(b) filter3 (590nm cut off)
(c) filter4 (665nm cut off)
(d) filter5 (715nm cut off)
<Figure 5. Measurement of output voltage with smaller step than figure 4. Dotted vertical
lines in each panel represent cut off wavelength, respectively>
As we can see from figure 4 and 5, filters looks working well in designated cut off
wavelengths. But I need to measure output with given wavelength exactly. Due to only
one RS232 cable, it is hard to measure output in a given wavelength by monochromator.
In addition, filter2 (a figure 4 & 5) plot is different above 330nm. And since output is
saturated above the cut off wavelengths, we can not see any slope or change above cut off
wavelengths. So we need to decrease the power of light source not to be saturated in the
long wavelength.
I measured the output again using fitler4 with multiple RS232 connectors with
appropriate intensity of light source. But measurement using current my IDL code can
not exactly match to the specific wavelength as you can see from figure 6. Measurement
value with IDL code is different to directly measured one which is measured with fixed
wavelength without using scan rate. This difference is caused by continuously varying of
monochroamtor’s gratings when I use the scan rate command.
<Figure6. Comparison of filter 3 with and without our IDL code to read the output>
NEXT Task.
I will update my IDL code to read exactly output signal of photodiode in a given
wavelength with an appropriate intensity of light and find characteristics of long pass
filters installed in monochromator.