Tham khảo tài liệu 'recent optical and photonic technologies 2012 part 13', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | 346 Recent Optical and Photonic Technologies We investigated the temporal response of a 10x10 pm2 4-PND-R probed with light at pm wavelength using a 40 GHz sampling oscilloscope Figure . All four possible amplitudes can be observed. The pulses show a full width at half maximum FWHM as low as 660ps. In a traditional 10x10 pm2 SSPD the pulse width would be of the order of 10 ns FWHM so the recovery of the output current Iout through the amplifier input resistance is a factor 42 faster see section which agrees with results reported by other groups Gol tsman et al. 2007 Tarkhov et al. 2008 . As shown in section the very attractive N2 scaling rule for the output pulse duration unfortunately does not apply to the device recovery time. Proof of PNR capability Let an N-PND be probed with a light whose photon number probability distribution is S S m sm . The probability distribution of the number of measured photons Q Q n qn is related to S by the relation Q n 2pN n I ni .s m 1 m where PN n m is the probability that n photons are detected when m are sent to the device. To infer whether a PND is able to measure the number of incoming photons it can be probed with a Poissonian distribution S m pm-exp -p m p mean photon number . The limited efficiency n 1 of the detector is equivalent to an optical loss and reduces the mean photon number to p np. In the regime p 1 S m p m and for p low enough 1 can be written as Q n P n I n -s n x ii n for ụ 1 2 Consequently the probability Q 1 of detecting one photon is proportional to p Q 2 is proportional to p2 and so on. A 10x10 pm2 5-PND-R was tested with the coherent light of GaAs pulsed laser Ấ 850 nm 30 ps pulse width 100kHz repetition rate whose photon number distribution is close to a Poissonian. The photoresponse from the device was sent to a 150 MHz counter. The detection probabilities relative to one- two- and three-photon absorption events are plotted for p varying from to 40 in Figure . As the mean .
