Spectrally resolved single-shot wavefront sensing of broadband high-harmonic sources

Wavefront sensors are an important tool to characterize coherent beams of extreme ultraviolet radiation. However, conventional Hartmann-type sensors do not allow for independent wavefront characterization of different spectral components that may be present in a beam, which limits their applicability for intrinsically broadband high-harmonic generation (HHG) sources. Here we introduce a wavefront sensor that measures the wavefronts of all the harmonics in a HHG beam in a single camera exposure. By replacing the mask apertures with transmission gratings at different orientations, we simultaneously detect harmonic wavefronts and spectra, and obtain sensitivity to spatiotemporal structure such as pulse front tilt as well. We demonstrate the capabilities of the sensor through a parallel measurement of the wavefronts of 9 harmonics in a wavelength range between 25 and 49 nm, with up to lambda/32 precision.Comment: 12 pages, 6 figure

Large Cavity Single Layer Quantum Dot Laser Diodes

Large cavity, very low threshold single layer quantum dot laser diodes with threshold current density of 10 A/cm2, output power \u3e 2 W, and very-low internal loss of 0.25 cm-1 are achieved at CW room-temperature. Mode-locked operation of a large cavity laser diode with 40 μm stripe width is demonstrated at 3.75 GHz repetition rate. ©2008 IEEE

Spectrally resolved wavefront characterization of broadband ultrafast high-harmonic pulses

We demonstrate a sensor that measures wavefronts of multiple extreme ultraviolet wavelengths simultaneously. By incorporating transmission gratings into the apertures of a Hartmann mask, we can record wavefront information for series of discrete harmonics from a high-harmonic generation source in a single camera exposure, without the need for scanning parts. Wavefronts of up to nine high harmonics at 25-49 nm wavelength are retrieved, and ultrafast spatiotemporal couplings can be detected

Spectrally resolved wavefront characterization of broadband ultrafast high-harmonic pulses

We demonstrate a sensor that measures wavefronts of multiple extreme ultraviolet wavelengths simultaneously. By incorporating transmission gratings into the apertures of a Hartmann mask, we can record wavefront information for series of discrete harmonics from a high-harmonic generation source in a single camera exposure, without the need for scanning parts. Wavefronts of up to nine high harmonics at 25-49 nm wavelength are retrieved, and ultrafast spatiotemporal couplings can be detected

Nanophotonic Lasers And Spontaneous Light Sources: Scaling Trends For Speed, Efficiency, And Quantum Light Generation Using Single Quantum Dots

Theory and experimental results for nophotonic devices based on epitaxial nanostructures will be presented. The devices include new types of quantum light sources, high speed nanoscale laser diodes, and energy conversion devices for havesting thermal energy. © 2007 IEEE

Quantum Dot Laser Diode With Low Threshold And Low Internal Loss

Data are presented demonstrating that a low-threshold quantum dot laser diode can achieve very low internal optical loss. The broad-area laser diode operates at the wavelength 1.22m and delivers 2W of power from a 1.6cm-long cavity with uncoated facets, with a lasing threshold current density of 10.4A/cm2. The laser diode\u27s internal waveguide loss is extracted from cavity length measurements to be ∼0.25cm-1. The interdependence of threshold current density and internal optical loss is discussed. © 2009 The Institution of Engineering and Technology

Physics Of Quantum Dot Lasers: Threshold Temperature Dependence, Internal Loss Effects, And Threshold Current Density

The physics of quantum dot lasers are studied theoretically and experimentally to study their threshold temperature dependence, and the relationship between internal loss and threshold current density. ©2008 IEEE

Simultaneous Deterministic Control Of Distant Qubits In Two Semiconductor Quantum Dots

In optimal quantum control (OQC), a target quantum state of matter is achieved by tailoring the phase and amplitude of the control Hamiltonian through femtosecond pulse-shaping techniques and powerful adaptive feedback algorithms. Motivated by recent applications of OQC in quantum information science as an approach to optimizing quantum gates in atomic and molecular systems, here we report the experimental implementation of OQC in a solid-state system consisting of distinguishable semiconductor quantum dots. We demonstrate simultaneous high-fidelity π and 2π single qubit gates in two different quantum dots using a single engineered infrared femtosecond pulse. These experiments enhance the scalability of semiconductor-based quantum hardware and lay the foundation for applications of pulse shaping to optimize quantum gates in other solid-state systems. © 2013 American Chemical Society

Very low threshold current density continuous-wave quantum dot laser diode

An important advantage of the quantum dot (QD) laser diode is its ability to reach lasing threshold at very low current density under continuous-wave room temperature operation. This can reduce or eliminate the need for heat sinking in large area laser diodes, and is one of the requirements to reach very high efficiency. Early work on quantum dot laser diodes demonstrated continuous-wave lasing at 19 A/cm2 [1], which was reduced to 17 A/cm2 in subsequent work [2]. In this presentation we report continuous-wave room temperature lasing at a threshold current density of 11.7 A/cm2. To our knowledge this is the lowest threshold current density ever reported for continuous-wave room temperature operation of a laser diode. The broad area laser diodes operate at 1.22 μm have a stripe width of 120 μm and cavity lengths of either 1 cm or 2 cm. The laser facets are left uncoated. As shown in Fig. 1, the 1 cm long laser diode mounted p-side down on a heat sink operates with a room temperature continuous-wave lasing threshold of ∼13 A/cm 2 and delivers up to 1 W of CW power from both facets. Figure 2 shows the CW lasing characteristics of a 2 cm long laser diode operated p-side up on a probe station. No bonding material is used between the substrate and laser diode, so that heat is dissipated mainly through current spreading into the substrate and contact cooling to the metal plate of the probe station. Despite the lack of heat sinking the laser diode operates with a record low room temperature CW threshold of 11.7 A/cm2 and delivers over 0.4 W of power from both facets. Figure 3 shows the spectral measurements and spectral narrowing for a range of room temperature CW current densities. We believe the initial reduction in the spectral width from 2 to 5 A/cm2 is due to preferential emission coming from the peak of the QD ensemble emission. However for current densities greater than ∼ 6 A/cm2 the spectral narrowing is due to stimulated emission. For current density greater than 10 A/cm2 this spectral narrowing due to stimulated emission has a rapid onset to lasing threshold with a total spectral width of a few meV. Therefore the transparency current density in these QD laser diodes under CW room temperature operation is \u3c 6 A/cm2. We believe that reaching very low threshold current density laser operation may have important implications for future technology based on large area or broad area monolithic laser diodes because of importance of threshold current density in heat sinking. ©2008 IEEE