Core-shell PbS-CdS quantum dots enhance the peak external quantum efficiency of shortwave-infrared light-emitting devices by up to 50-100-fold (compared with core-only PbS devices). This is more than double the efficiency of previous quantum-dot light-emitting devices operating at wavelengths beyond 1 μm, and results from the passivation of the PbS cores by the CdS shells against in situ photoluminescence quenching.

Femtosecond high-order harmonic transient absorption spectroscopy is used to resolve the complete |j, m quantum state distribution of Xe + produced by optical strong-field ionization of Xe atoms at 800 nm. Probing at the Xe N 4/5 edge yields a population distribution ρ j,|m| of ρ 3/2,1/2 : ρ 1/2,1/2 : ρ 3/2,3/2 = 75 ± 6 : 12 ± 3 : 13 ± 6%. The result is compared to a tunnel ionization calculation with the inclusion of spin-orbit coupling, revealing nonadiabatic ionization behavior. The sub-50-fs time resolution paves the way for table-top extreme ultraviolet absorption probing of ultrafast dynamics.PACS numbers: 42.50. Hz, 32.80.Rm, 42.65.Ky, Studies of laser-atom interactions in the nonperturbative, strong-field regime elucidate novel phenomena such as above-threshold ionization [1,2], nonsequential double ionization [3], and high-order harmonic generation [4,5,6]. While these processes are extensively studied both experimentally and theoretically, details remain unknown about the |j, m state distribution of the photoion produced by the initial photoionization step (m is the projection quantum number associated with the total angular momentum j of the hole). Moreover, experimental tests of theoretical models for strong-field ionization mostly rely on measuring the ion yield as a function of laser peak intensity [7]. The strong dependence of ionization yields on the orbital angular momentum and its direction relative to the laser polarization axis, as predicted by most theoretical models (e.g., the Ammosov-Delone Krainov (ADK) rates [8]), suggests that knowledge of the complete |j, m state distribution can be used as an additional benchmark for theory. Young et al. recently reported the use of synchrotron x-ray pulses to probe the hole-orbital alignment of Kr + photoions generated in the strong-field ionization of Kr [9]. The unresolved finestructure transitions prevented retrieval of the complete |j, m state distribution. However, the observed degree of alignment is reproduced by the |j, m state distribution obtained by tunnel ionization calculations with the inclusion of spin-orbit coupling [10].Here we investigate the experimental and theoretical strong-field ionization of xenon to extract the complete |j, m quantum state distribution. Femtosecond extreme ultraviolet (EUV) transient absorption spectroscopy is demonstrated with a laser-based, high-order harmonic probe source for the experiments; results are compared to tunnel ionization calculations that incorporate spinorbit coupling. The resultant angular momentum distribution and hole-orbital alignment of the Xe + photoions are measured by probing the transition from the 4d core level to the 5p valence shell. These measurements allow the determination of the complete |j, m quantum state distribution, which is compared to theory.The schematic of the experimental setup is illustrated in Fig. 1. Briefly, the amplified output from a commercial Ti:sapphire laser system (2.4 W, 800 nm, 45 fs, 1 kHz) is sent to a 20 : 80 beamsplitter to produce the optical pump an...

Experimental restrictions imposed on the collection and detection of shortwave-infrared photons (SWIR) have impeded single molecule work on a large class of materials whose optical activity lies in the SWIR. Here we report the successful observation of room-temperature single nanocrystal photoluminescence at SWIR wavelengths using a highly efficient multielement superconducting nanowire single photon detector. We confirm that the photoluminescence from single lead sulfide nanocrystals is strongly antibunched, demonstrating the feasibility of performing sophisticated photon correlation experiments on individual weak SWIR emitters, and, more broadly, paving the way for sensitive measurements of spectral observables on infrared quantum systems that are incompatible with current detection techniques.

We present a quantitative measurement of the number of trapped carriers combined with a measurement of exciton quenching to assess limiting mechanisms for current losses in PbS-quantum-dot-based photovoltaic devices. We use photocurrent intensity dependence and short-wave infrared transient photoluminescence and correlate these with device performance. We find that the effective density of trapped carriers ranges from 1 in 10 to 1 in 10,000 quantum dots, depending on ligand treatment, and that nonradiative exciton quenching, as opposed to recombination with trapped carriers, is likely the limiting mechanism in these devices.