Light spanning the near infrared to the ultraviolet has been confined in pulses shorter than a single optical cycle.

Cesium lead bromide (CsPbBr₃) perovskite has recently gained significance owing to its rapidly increasing performance when used for light-emitting devices. In this study, we used density functional theory to determine the structural, electronic, and optical properties of the cubic, tetragonal, and orthorhombic temperature-dependent phases of CsPbBr₃ perovskite using the full-potential linear augmented plane wave method. The electronic properties of CsPbBr₃ perovskite have been investigated by evaluating their changes upon exerting spin-orbit coupling (SOC). The following exchange potentials were used: the local density approximation (LDA), Perdew–Burke–Ernzerhof generalized gradient approximation (PBE-GGA), Engel–Vosko GGA (EV-GGA), Perdew–Burke–Ernzerhof GGA revised for solids (PBEsol-GGA), modified Becke–Johnson GGA (mBJ-GGA), new modified Becke–Johnson GGA (nmBJ-GGA), and unmodified Becke–Johnson GGA (umBJ-GGA). Our band structure results indicated that the cubic, tetragonal, and orthorhombic phases have direct energy bandgaps. By including the SOC effect in the calculations, the bandgaps computed with mBJ-GGA and nmBJ-GGA were found to be in good agreement with the experimental results. Additionally, despite the large variations in their lattice constants, the three CsPbBr₃ phases possessed similar optical properties. These results demonstrate a wide temperature range of operation for CsPbBr₃.

We investigate power scaling of ultrashort-pulse enhancement cavities. We propose a model for the sensitivity of a cavity design to thermal deformations of the mirrors due to the high circulating powers. Using this model and optimized cavity mirrors, we demonstrate 400 kW of average power with 250 fs pulses and 670 kW with 10 ps pulses at a central wavelength of 1040 nm and a repetition rate of 250 MHz. These results represent an average power improvement of one order of magnitude compared to state-of-the-art systems with similar pulse durations and will thus benefit numerous applications such as the further scaling of tabletop sources of hard x rays (via Thomson scattering of relativistic electrons) and of soft x rays (via high harmonic generation).

A passive optical resonator is used to enhance the power of a pulsed $78\mathrm{MHz}$ repetition rate Yb laser providing $200\mathrm{fs}$ pulses. We find limitations relating to the achievable time-averaged and peak power, which we distinguish by varying the duration of the input pulses. An intracavity average power of $18\mathrm{kW}$ is generated with close to Fourier-limited pulses of $10\mathrm{W}$ average power. Beyond this power level, intensity-related effects lead to resonator instabilities, which can be removed by chirping the seed laser pulses. By extending the pulse duration in this way to $2\mathrm{ps}$, we could obtain $72\mathrm{kW}$ of intracavity circulating power with $50\mathrm{W}$ of input power.