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Quantum cascade lasers are compact, electrically pumped light sources in the technologically important mid-infrared and terahertz region of the electromagnetic spectrum 1 , 2 . Recently, the concept of topology 3 has been expanded from condensed matter physics into photonics 4 , giving rise to a new type of lasing 5 – 8 using topologically protected photonic modes that can efficiently bypass corners and defects 4 . Previous demonstrations of topological lasers have required an external laser source for optical pumping and have operated in the conventional optical frequency regime 5 – 8 . Here we demonstrate an electrically pumped terahertz quantum cascade laser based on topologically protected valley edge states 9 – 11 . Unlike topological lasers that rely on large-scale features to impart topological protection, our compact design makes use of the valley degree of freedom in photonic crystals 10 , 11 , analogous to two-dimensional gapped valleytronic materials 12 . Lasing with regularly spaced emission peaks occurs in a sharp-cornered triangular cavity, even if perturbations are introduced into the underlying structure, owing to the existence of topologically protected valley edge states that circulate around the cavity without experiencing localization. We probe the properties of the topological lasing modes by adding different outcouplers to the topological cavity. The laser based on valley edge states may open routes to the practical use of topological protection in electrically driven laser sources. A topological laser based on the valley degree of freedom in a compact photonic crystal can be pumped electrically, bringing topological physics concepts closer to real-life applications.

We present a multi-mode diode-pumped Yb:CALGO laser oscillator based on cross-polarization pumping. Using this method, we demonstrate 22-fs pulses at 0.3 W, which is the shortest duration for any Yb- based bulk laser oscillator utilizing multimode-diode pumping.

Organic semiconductors are carbon-based materials that combine optoelectronic properties with simple fabrication and the scope for tuning by changing their chemical structure 1 – 3 . They have been successfully used to make organic light-emitting diodes 2 , 4 , 5 (OLEDs, now widely found in mobile phone displays and televisions), solar cells 1 , transistors 6 and sensors 7 . However, making electrically driven organic semiconductor lasers is very challenging 8 , 9 . It is difficult because organic semiconductors typically support only low current densities, suffer substantial absorption from injected charges and triplets, and have additional losses due to contacts 10 , 11 . In short, injecting charges into the gain medium leads to intolerable losses. Here we take an alternative approach in which charge injection and lasing are spatially separated, thereby greatly reducing losses. We achieve this by developing an integrated device structure that efficiently couples an OLED, with exceptionally high internal-light generation, with a polymer distributed feedback laser. Under the electrical driving of the integrated structure, we observe a threshold in light output versus drive current, with a narrow emission spectrum and the formation of a beam above the threshold. These observations confirm lasing. Our results provide an organic electronic device that has not been previously demonstrated, and show that indirect electrical pumping by an OLED is a very effective way of realizing an electrically driven organic semiconductor laser. This provides an approach to visible lasers that could see applications in spectroscopy, metrology and sensing. An electrically driven organic semiconductor laser is achieved by integrating a device structure that efficiently couples an organic light-emitting diode, with extremely high internal-light generation, with a polymer distributed feedback laser.

Improving the efficiency of lasers without complex structures, expensive elements, and precise optimization will lead to cost reductions and increased practicality. Here, it is first shown theoretically that the dependence of the optical-to-optical conversion efficiency on the laser beam waist (minimum laser spot) radii for a Yb:YAG laser with a simple structure decreases extremely with increasing pump intensity and efficiency. Not only is the optimum range for highest efficiency wide, but even if the radii are doubled, the efficiency decreases by only a few percentage points or less at the maximum pump intensity of 450 kW/cm2. Therefore, it is possible to achieve sufficiently high efficiencies without precise optimization by high-intensity pumping. In the experiment, at a pump wavelength of 940 nm, corresponding to pump-level pumping, the maximum efficiency was 75.2% for the incident pump power at the corresponding maximum intensity. On the other hand, at a pump wavelength of 968 nm, corresponding to direct pumping of the upper laser level, the maximum efficiency was 76.0% at about 60% of the maximum. Although the pump focus is slightly off from the optimum, these efficiencies are close to the theoretical maximum at the corresponding pump intensities. Since no complex gain medium is used, there is almost no efficiency reduction due to parasitic oscillations, despite the high pump intensities. These results demonstrate the high practicality of high-intensity pumping for high-efficiency lasers.

The time–energy information of ultrashort X-ray free-electron laser pulses generated by the Linac Coherent Light Source is measured with attosecond resolution via angular streaking of neon 1s photoelectrons. The X-ray pulses promote electrons from the neon core level into an ionization continuum, where they are dressed with the electric field of a circularly polarized infrared laser. This induces characteristic modulations of the resulting photoelectron energy and angular distribution. From these modulations we recover the single-shot attosecond intensity structure and chirp of arbitrary X-ray pulses based on self-amplified spontaneous emission, which have eluded direct measurement so far. We characterize individual attosecond pulses, including their instantaneous frequency, and identify double pulses with well-defined delays and spectral properties, thus paving the way for X-ray pump/X-ray probe attosecond free-electron laser science.

We report on polarized spectroscopy and orange laser operation under 2ω-OPSL and GaN-diode pumping of Sm:LiYF4 crystals. The Samarium laser delivers 12 mW at 605 nm with a threshold of 51 mW and a linear polarization.

A Tm:LiYF4 laser operating on the 3H4→3H5 transition with upconversion pumping at 1.45 µm generates 831 mW at 2313 nm with 34.0% slope efficiency. Mode-locked by a GaSb- based SESAM, it delivers 855-fs pulses at 104.4-MHz.

Electrically pumped organic lasing is one of the most challenging issues in organic optoelectronics. We present a systematic theoretical investigation to screen out electrical pumping lasing molecules over a wide range of organic materials. With the electronic structure information obtained from time-dependent density functional theory, we calculate multiple photophysical parameters of a set of optical pumping organic laser molecules in our self-developed molecular material property prediction package (MOMAP) to judge whether the electrically pumped lasing conditions can be satisfied, namely, to avoid reabsorption from excitons and/or polarons, and the accumulation of triplet excitons. In addition, a large oscillator strength of S 1 and weak intermolecular π–π interaction are preferred. With these criteria, we are able to conclude that BP3T, BSBCz, and CzPVSBF compounds are promising candidates for electrically pumped lasing, and the proposed computational strategy could serve as a general protocol for molecular design of organic lasing materials. Though the goal of current organic solid-state laser research remains the realization of electrically pumped lasing, identifying organic semiconductors with ideal properties remains a challenge. Here, the authors report a computational strategy for screening electrical pumping lasing molecules.

Electro-optically Q-switched side-pumped diode-pumped KTP/YAG:Nd3+ nanosecond laser system with an intracavity collinear optical parametric oscillation was proposed as a pump source for Cr2+:ZnSe laser. Energy parameters of Cr2+:ZnSe laser were investigated with respect to the wavelength of the pump laser. Under optimal conditions, pumping with laser pulses with an energy of 10.5 mJ and a duration of 7.2 ns at a wavelength of 1950 nm allowed to obtain 3.2 ns pulses at a wavelength of 2494 nm with slope optical-to-optical conversion efficiency of 5.5%.