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Novel contribution in branch of ultra-fast condensed matter spectroscopic photon counting system
MicroelectronicEngineering 19 (1992) 643-648 Elsevier
643
NOVEL CONTRIBUTION IN BRANCH OF ULTRA-FAST CONDENSED M A T T E R SPECTROSCOPIC PHOTON COUNTING SYSTEM I.Prochgtzka, K.Hamal, B.Sopko, I.M~icha Czech Technical University, Brehova 7, 115 19 Prague, Czechoslovakia
ABSTRACT We are reporting on the novel design of an all solid state photon counting package and its applications in ultrafast spectroscopy. Developing the new active gating and quenching circuit of the diode we achieved the short and precisely defined detector dead time, the fast gate response and simultaneously the circuit simplicity and compactness.
1. PRINCIPLE OF OPERATION The application of the solid state detector in the photon counting device operating at the room temperature and having a diameter of 8-40 microns has been reported by S.Cova [1]. In our design we focused on the diode structure design and the chip manufacturing technology, our latest technology achievements permitted to increase the diode active area diameter up to 100 microns while still maintaining an acceptable dark count rate at a room temperature and a fast response, as ~vell. The photon counting package consists of the in house manufactured Single Photon Avalanche Diode (SPAD) and the gating and quenching electronics. The SPAD is a diode structure manufactured using a conventional planar technology on Silicon. The single photon sensitivity is achieved by biasing the diode above the junction break voltage. In this stage, the first absorbed photon is capable of triggering the avalanche multiplication of carriers - the fast risetime current pulse is generated. Its amplitude is limited only by the external circuit connected to the diode. Following the idea of S.Cova we developed the active quenching circuit, which decreases the voltage applied to the diode bellow the break voltage as soon as an avalanche current buildup is detected. The diode voltage is kept bellow the break for the fixed interval adjustable within a few tens of nanoseconds to units of microseconds. Then, the diode is biased above the break, again. Two principal mode of operation are available : 1. Gated mode : the external electrical gate / pre-trigger signal is applied a short time before the expected arrival of the photon to be detected. In the "gate off" state, the detector sensitivity is decreased about 10 9 times. There are several advantages of this mode : the possibility to study the weak optical signal short after a strong one, namely in fluorescence studies. The detection chips active area diameters of up to 100 microns may be used. 2. Continuous counting mode : the gate signal is permanently on. The detector may be 0167-9317/92/$05.00 © 1992 - Elsevier Science Publishers B.V. All rights reserved.
644
I. Prochrzka et al. / Condensed matter spectroscopic photon counting ~Zystem
used for the count rate reaching 107 counts / second. Due to the lack of the external gating this mode is very easy to use. However, only the detection chip having active area not bigger than 40 microns in diameter may be used. 2. CONSTRUCTION The SPAD together with the active quenching and gating circuits are housed in a compact cylindrical housing 40 millimeters in diameter, 120 millimeters long with the detector in the center of the front face. The optional input collecting optics accepting a collimated beam of up to 14 millimeter in diameter and a thermoelectric cooler may be included. On the package output the user gets the uniform pulses : NIM or TTL or ECL on request. The external GATE signal may be applied. The "Gate ON" delay is shorter than 25 nanoseconds. The external biases +/-6 Volts and -30 Volts are needed only. Detecting a single photon the diode generates an uniform electrical signal on low impedance of the amplitude of Volts. Thanks to this extremely high gain within the diode itself no signal amplification and discrimination is needed in the detector package. Omitting the signal amplification and discrimination, usually needed for standard photon counting systems, the excellent system temporal stability is achieved. The internal delay is changing less than 5 picoseconds within hours. Thanks to low power and low voltages, the power supplies may be simply stabilized and compensated within the wide temperature range. Special voltage stabilizer has been developed to maintain the diode bias voltage within the temperature range of -60 to + 100 Centigrade. 3. APPLICATIONS AND P E R F O R M A N C E The application of this photon counting package in the subcentimeter satellite laser ranging and in the space born laser altimetry has been reported [2,3]. In all the applications the detector simplicity, compact design, wide temperature range and a low voltage and power requirements are attractive features. The spectroscopy application performance tests have been carried out at the Applied Physics Institute of University of Bern. For this tests the 20 microns diameter diode biased 0.3 to 1.5 Volts above break has been delechon probablhty used. The detector has been interfaced to the 50 micron diameter multimode fiber using two microscope objectives. Using the calibrated light source and the calibrated set of filters the detection probability has been found to reach 10 percent at the wavelength 0.8 micron when biasing the diode 1 Volt above the break voltage. i i i :: Biasing the diode 3-4 Volts above the [39 04 05 05 0.7 0.8 09 tl break voltage, the detection probability wavelength [microns] may be increased 2-3 times while the dark 2[lum chlp,contmous mode,O 3V above bf count rate is increased at the same factor. The detection sensitivity spans over the Figure 1 Detection probability versus waveinterval between 0.35 and 1.1 micron, the length
1o~:.i!
645
I. Proch6zka et al. / Condensed matter spectroscopic photon counting system
curve of the sensitivity versus wavelength is plotted on Figure 1. Using the 300 femtoseconds pulses at the 0.8 micron wavelength, the timing resolution has been found to be better than 100 picoseconds at FWHM, see Figure 2. These measurements have been carded out of counts 500 at the Institute of Applied Physics: Uviv. A 300 lsec laser of Bern in cooperation with Dr.J.Ri~ka et liming syst.conlrib. 85 psec 400 2; rueImensg;hD0'1!5UVma bove al. One has to keep in mind, that the resulting curve is a convolution of the 300 laser pulse length (which is negligible in 200 this experiment), the time interval measuring electronics and the detection package 100 contribution. Deconvoluting the electronics contribution, one gets the timing resolution 10 2D 30 40 5D 6D ?0 80 90 100 of the detector package better than 60 time 115 psec/channell picoseconds at FWHM. The detection dead time is adjust- Figure 2 Timing resolution able to the values lower than 100 nanoseconds when using the 20 micrometers diameter chip; the counting linearity is plotted on Figure 3. Using the picosecond diode laser pulser the dynamical range/the detection delay versus an optical signal strength/of the detector has been tested. For most of the conventional photon counting systems the detection delay is substantially lower for multiphoton detection. In our measurements we did fir~d, that for the signal strength 1 to 30 photons detected, the detector delay changes less than +/-13 picoseconds. 4. CONCLUSION An all solid state photon counting system described above might find its application in spectroscopy, fluorescence studies, Raman spectroscopy and others, where the optical signal may be focused on a small spot. The detector simplicity, picosecond stability and resolution, dynamical range and count rate are the most attractive features.
count rale colrectlon
3. . . . . . . . . .
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0 5 ,- ....... !--- "!'" ~ " ! ' ! ' ! ' ! ' H . . . . . . . . ~ " " ! " ' ! " ! " ~ O'
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REFERENCES
i
i
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i
i
i iliii'
!'!!', ........ !'" " ' ! ' " ! " ! ' ! ' ! ' ! ' ! ;
;
,
; ilili'
~oo moo registered count rale IkHzl 20urn chip,continous mode, O.3V above bL
1oooo
1.S.Cova et aI,IEEE J.Q.Electronics, QE- Figure 3 Counting linearity 19,630(1983) 2.I.Prochazka et al, proc. of the Conference on Lasers and Electro OpticsCLEO'90, Anaheim, California, May 1990 3.S.Pershin et al, proc. of the Conference on Lasers and Electro Optics,CLEO'91, Baltimore, MD, May 1991
643
NOVEL CONTRIBUTION IN BRANCH OF ULTRA-FAST CONDENSED M A T T E R SPECTROSCOPIC PHOTON COUNTING SYSTEM I.Prochgtzka, K.Hamal, B.Sopko, I.M~icha Czech Technical University, Brehova 7, 115 19 Prague, Czechoslovakia
ABSTRACT We are reporting on the novel design of an all solid state photon counting package and its applications in ultrafast spectroscopy. Developing the new active gating and quenching circuit of the diode we achieved the short and precisely defined detector dead time, the fast gate response and simultaneously the circuit simplicity and compactness.
1. PRINCIPLE OF OPERATION The application of the solid state detector in the photon counting device operating at the room temperature and having a diameter of 8-40 microns has been reported by S.Cova [1]. In our design we focused on the diode structure design and the chip manufacturing technology, our latest technology achievements permitted to increase the diode active area diameter up to 100 microns while still maintaining an acceptable dark count rate at a room temperature and a fast response, as ~vell. The photon counting package consists of the in house manufactured Single Photon Avalanche Diode (SPAD) and the gating and quenching electronics. The SPAD is a diode structure manufactured using a conventional planar technology on Silicon. The single photon sensitivity is achieved by biasing the diode above the junction break voltage. In this stage, the first absorbed photon is capable of triggering the avalanche multiplication of carriers - the fast risetime current pulse is generated. Its amplitude is limited only by the external circuit connected to the diode. Following the idea of S.Cova we developed the active quenching circuit, which decreases the voltage applied to the diode bellow the break voltage as soon as an avalanche current buildup is detected. The diode voltage is kept bellow the break for the fixed interval adjustable within a few tens of nanoseconds to units of microseconds. Then, the diode is biased above the break, again. Two principal mode of operation are available : 1. Gated mode : the external electrical gate / pre-trigger signal is applied a short time before the expected arrival of the photon to be detected. In the "gate off" state, the detector sensitivity is decreased about 10 9 times. There are several advantages of this mode : the possibility to study the weak optical signal short after a strong one, namely in fluorescence studies. The detection chips active area diameters of up to 100 microns may be used. 2. Continuous counting mode : the gate signal is permanently on. The detector may be 0167-9317/92/$05.00 © 1992 - Elsevier Science Publishers B.V. All rights reserved.
644
I. Prochrzka et al. / Condensed matter spectroscopic photon counting ~Zystem
used for the count rate reaching 107 counts / second. Due to the lack of the external gating this mode is very easy to use. However, only the detection chip having active area not bigger than 40 microns in diameter may be used. 2. CONSTRUCTION The SPAD together with the active quenching and gating circuits are housed in a compact cylindrical housing 40 millimeters in diameter, 120 millimeters long with the detector in the center of the front face. The optional input collecting optics accepting a collimated beam of up to 14 millimeter in diameter and a thermoelectric cooler may be included. On the package output the user gets the uniform pulses : NIM or TTL or ECL on request. The external GATE signal may be applied. The "Gate ON" delay is shorter than 25 nanoseconds. The external biases +/-6 Volts and -30 Volts are needed only. Detecting a single photon the diode generates an uniform electrical signal on low impedance of the amplitude of Volts. Thanks to this extremely high gain within the diode itself no signal amplification and discrimination is needed in the detector package. Omitting the signal amplification and discrimination, usually needed for standard photon counting systems, the excellent system temporal stability is achieved. The internal delay is changing less than 5 picoseconds within hours. Thanks to low power and low voltages, the power supplies may be simply stabilized and compensated within the wide temperature range. Special voltage stabilizer has been developed to maintain the diode bias voltage within the temperature range of -60 to + 100 Centigrade. 3. APPLICATIONS AND P E R F O R M A N C E The application of this photon counting package in the subcentimeter satellite laser ranging and in the space born laser altimetry has been reported [2,3]. In all the applications the detector simplicity, compact design, wide temperature range and a low voltage and power requirements are attractive features. The spectroscopy application performance tests have been carried out at the Applied Physics Institute of University of Bern. For this tests the 20 microns diameter diode biased 0.3 to 1.5 Volts above break has been delechon probablhty used. The detector has been interfaced to the 50 micron diameter multimode fiber using two microscope objectives. Using the calibrated light source and the calibrated set of filters the detection probability has been found to reach 10 percent at the wavelength 0.8 micron when biasing the diode 1 Volt above the break voltage. i i i :: Biasing the diode 3-4 Volts above the [39 04 05 05 0.7 0.8 09 tl break voltage, the detection probability wavelength [microns] may be increased 2-3 times while the dark 2[lum chlp,contmous mode,O 3V above bf count rate is increased at the same factor. The detection sensitivity spans over the Figure 1 Detection probability versus waveinterval between 0.35 and 1.1 micron, the length
1o~:.i!
645
I. Proch6zka et al. / Condensed matter spectroscopic photon counting system
curve of the sensitivity versus wavelength is plotted on Figure 1. Using the 300 femtoseconds pulses at the 0.8 micron wavelength, the timing resolution has been found to be better than 100 picoseconds at FWHM, see Figure 2. These measurements have been carded out of counts 500 at the Institute of Applied Physics: Uviv. A 300 lsec laser of Bern in cooperation with Dr.J.Ri~ka et liming syst.conlrib. 85 psec 400 2; rueImensg;hD0'1!5UVma bove al. One has to keep in mind, that the resulting curve is a convolution of the 300 laser pulse length (which is negligible in 200 this experiment), the time interval measuring electronics and the detection package 100 contribution. Deconvoluting the electronics contribution, one gets the timing resolution 10 2D 30 40 5D 6D ?0 80 90 100 of the detector package better than 60 time 115 psec/channell picoseconds at FWHM. The detection dead time is adjust- Figure 2 Timing resolution able to the values lower than 100 nanoseconds when using the 20 micrometers diameter chip; the counting linearity is plotted on Figure 3. Using the picosecond diode laser pulser the dynamical range/the detection delay versus an optical signal strength/of the detector has been tested. For most of the conventional photon counting systems the detection delay is substantially lower for multiphoton detection. In our measurements we did fir~d, that for the signal strength 1 to 30 photons detected, the detector delay changes less than +/-13 picoseconds. 4. CONCLUSION An all solid state photon counting system described above might find its application in spectroscopy, fluorescence studies, Raman spectroscopy and others, where the optical signal may be focused on a small spot. The detector simplicity, picosecond stability and resolution, dynamical range and count rate are the most attractive features.
count rale colrectlon
3. . . . . . . . . .
2.5
2 it ii i!i r. . . .
1.5
0 5 ,- ....... !--- "!'" ~ " ! ' ! ' ! ' ! ' H . . . . . . . . ~ " " ! " ' ! " ! " ~ O'
,o
REFERENCES
i
i
i ilili'
i
i
i iliii'
!'!!', ........ !'" " ' ! ' " ! " ! ' ! ' ! ' ! ' ! ;
;
,
; ilili'
~oo moo registered count rale IkHzl 20urn chip,continous mode, O.3V above bL
1oooo
1.S.Cova et aI,IEEE J.Q.Electronics, QE- Figure 3 Counting linearity 19,630(1983) 2.I.Prochazka et al, proc. of the Conference on Lasers and Electro OpticsCLEO'90, Anaheim, California, May 1990 3.S.Pershin et al, proc. of the Conference on Lasers and Electro Optics,CLEO'91, Baltimore, MD, May 1991