Temporal And Spectral Control Of Single-photon Frequency Upconversion Detection For Pulsed Radiation

Recently, high efficient infrared single-photon detectors draw a lot of attention due to their wide applications, such as astronomy, quantum key distribution, ultrasensitive spectroscopy, deep-space communication, laser sensing and ranging. The conventional infrared detectors as InGaAs avalanche photodiodes (APDs) show poor performance compared to that of Si APDs, which are available for visible single-photon detection. The superconductor detectors or the quantum dot detectors offer a superior performance for infrared single-photon detection, but they are prohibited from the widespread use by their high cost and extremely critical working conditions. Fortunately, single-photon frequency upconversion technique provides a novel solution. The infrared single photons could be converted to visible region with nearly unity efficiency under a strong pump field in a quadratic nonlinear medium, and then the converted photons can be handled by the Si APDs for high detection efficiency. Various infrared single-photon upconversion detectors have been realized in continuous-wave mode with high conversion efficiency. But the background noise mainly caused by the continuous-mode pump field limits the performance of those detectors.In order to achieve infrared single-photon upconversion detection with high efficiency and ultralow background noise, we developed a coincidence frequency upconversion detection scheme with a precise control in both temporal and spectral domains. With the help of fiber laser techniques, single-photon signals and the intense pump pulses are temporally synchronized while appropriately narrow spectra are obtained for approaching the acceptance bandwidth. The infrared signal and pump pulses were prepared experimentally by the synchronized mode-locked erbium doped fiber laser and ytterbium doped fiber laser, respectively. A periodically poled lithium niobate crystal (PPLN) was employed as the nonlinear media for frequency upconversion due to its wide transparent window, large nonlinear coefficient and long interaction length. With a specific concern about the temporal-and-spectral matching in frequency upconversion system, highly efficient single photon frequency upconversion detection was implemented with ultra-low background noise. Moreover, we demonstrated theoretically and experimentally that the converted visible photons were well temporally correlated with the unconverted infrared photons. Furthermore, the synchronously pulsed pumping frequency upconversion system was proved useful for photon-number-resolving detection and ultra-sensitive upconversion imaging. Additionally, the wavelength of single photon source in the frequency upconversion system was already extended from near infrared to mid-infrared regime.The main achievements and innovations of this thesis are summarized below:1. A single-photon frequency upconversion detection scheme based on the all-optical synchronization pumping technique was proposed. The conversion efficiency was significantly increased due to the temporal synchronization and spectral matching of the signal photons and pump pulses. Besides, the synchronous pump confines most of the noise within the ultra-short time window and the wavelength of the pump was chosen to be longer than that of signal, leading to effectively suppress of the background noise. Eventually, a high detection efficiency of80.5%has been realized with a corresponding low background noise of1.5kcps.2. The quantum features of the multi-longitudinal modes interaction during the upconversion process were analyzed theoretically. The experimental results indicated that the converted visible photon was in tight correlation with the unconverted infrared photon. The second-order temporal correlation was measured for proving the preservation of the coherence properties during the upconversion process.3. Benefited from the frequency upconversion system based on synchronously pulsed pumping, infrared photon-number-resolving detection and highly sensitive infrared imaging were achieved.a) Utilizing a Silicon multi-pixel photon counter, photon-number-resolving detection at1.04μm was realized. The total detection efficiency of the system was3.7%and the corresponding background noise probability was0.0002/pulse.b) The infrared object image was upconverted spectrally to the visible region with a conversion efficiency of33%using the frequency upconversion system mentioned above. The converted visible photons were then captured by a high performance electron multiplying CCDs, thus inferring the spatial information of the infrared object image.4. Mid-infrared single-photon frequency upconversion detection based on pulsed pumping was demonstrated experimentally. Specifically, the signal photons and the pump pulses came from a continuous-wave running He-Ne laser and a mode-locked ytterbium-doped fiber laser, respectively. The detection efficiency was measured to be6.1%, inferring a conversion efficiency of64%by correcting the transmittance of the filtering system. The background noise was reduced remarkably to400counts/s by the pulsed pump excitation.