Spectroscopic properties and continuous-wave deep-red laser operation of Eu3+-doped LiYF4.

Eu3+-doped LiYF4 is reexamined as a laser material for the visible spectral region. Polarized absorption and emission cross sections as well as the fluorescence lifetime are determined. Branching ratios and radiative lifetime are calculated within the theory of 4f-4f transition intensities, which takes into account the influence of an excited configuration of the opposite parity 4fN-15d. Continuous-wave laser operation at 702 nm is demonstrated with a maximum output power of 15 mW and a slope efficiency of 4.6% under pumping with a frequency-doubled Ti:sapphire laser at 393.5 nm.

Yb3+:LuAlO3 crystal as a gain medium for efficient broadband chirped pulse regenerative amplification.

The experimental study results of a chirped pulse amplification regime are reported for the Yb:LuAlO3 crystal with different polarization states in the gain media for the first time, to the best of our knowledge. Maximum output power of 5 W with 565 fs pulse duration was obtained for E//b-polarization at a 200 kHz repetition rate seeded by a 98 fs Yb:KYW oscillator. 165 fs pulses with output power of 4.5 W were demonstrated for E//c-polarized light in the crystal.

Growth, spectroscopy, and laser characterization of Er:KGdxYbyY1-x-y(WO4)2 epitaxial layers.

We report on the composition of Er-doped KGdxYbyY1-x-y(WO4)2 layers to be grown onto undoped KY(WO4)2 substrate providing fine lattice matching and high refractive index contrast with the substrate and fabrication of high optical quality Er(1.3 at. %):KGd0.2Yb0.15Y0.65(WO4)2 epitaxial layers with thickness up to 180 µm. Absorption and luminescence properties of the layer were measured and laser action under direct in-band pumping was reported for the first time, to our knowledge, in a non-waveguide configuration. A maximum output power of 16 mW with slope efficiency of 64% was achieved at 1606 nm.

Passively Q-switched Pr:YLF laser with a Co2+:MgAl2O4 saturable absorber.

We report on a 2ω-OPSL-pumped passively Q-switched Pr3+:LiYF4 laser operating at the wavelengths of 523, 607, and 640 nm. For this, we utilized a Co2+-doped MgAl2O4 (MALO) crystal as a saturable absorber in the visible range for the first time, to the best of our knowledge. In the green spectral region, the pulse duration was 210 ns with a pulse energy of 3.6 µJ and a repetition rate of 125 kHz. The minimum pulse duration of 87 ns at the highest pulse energy of 8.6 µJ was obtained at a repetition rate of 110 kHz at 607 nm. The highest Q-switched average laser power of 1.4 W was obtained at an absorbed continuous-wave pump power of 3.3 W with a slope efficiency of 47% at 640 nm. Absorption saturation measurements with Co:MALO were performed, and ground and excited state absorption cross sections in the visible spectral range were determined.

Graphene Q-switched Er,Yb:GdAl3(BO3)4 laser at 1550 nm.

A single-layer graphene saturable absorber is employed for passive Q-switching of an Er, Yb:GdAl3(BO3)4 (Er,Yb:GdAB) compact laser, representing the first Er-doped oxoborate laser Q-switched by graphene. This laser is based on a c-cut 1.8 at. % Er3+, 15 at. % Yb3+:GdAB crystal diode-pumped at 0.976 µm. It generates a maximum average output power of 360 mW at 1.55 µm with a slope efficiency of 23% (with respect to the incident power). Stable ∼1 µJ/130 ns pulses are achieved at a repetition rate of 400 kHz. This result represents, to the best of our knowledge, the shortest pulse duration ever achieved in bulk Er lasers Q-switched by 2D materials. Graphene is a promising material for generating nanosecond pulses at high repetition rates (MHz range) in Er-doped oxoborate lasers emitting in the eye-safe range at 1.5-1.7 µm.

Energy transfer in Tm,Ho:KYW crystal and diode-pumped microchip laser operation.

An investigation of Tm-Ho energy transfer in Tm(5at.%),Ho(0.4at.%):KYW single crystal by two independent techiques was performed. Based on fluorescence dynamics measurements, energy transfer parameters P71 and P28 for direct (Tm→Ho) and back (Ho→Tm) transfers, respectively, as well as equilibrium constant Θ were evaluated. The obtained results were supported by calculation of microscopic interaction parameters according to the Förster-Dexter theory for a dipole-dipole interaction. Diode-pumped continuous-wave operation of Tm,Ho:KYW microchip laser was demonstrated, for the first time to our knowledge. Maximum output power of 77 mW at 2070 nm was achieved at the fundamental TEM00 mode.

Spectroscopy and continuous wave laser performance of Yb3+:LuAlO3 crystal.

Crystal growth, polarized spectroscopic properties, lifetime measurements, and CW laser performance under diode pumping of a new Yb3+-doped LuAlO3 crystal (Yb:LuAP) are reported for the first time, to the best of our knowledge. The maximum absorption cross section of 6.6·10-20 cm2 at 978.5 nm was determined for E//c polarization. The radiative lifetime of F5/22 manifold of Yb3+ ions in LuAP was measured to be 475 µs. CW laser action was demonstrated with output powers up to 9.6 W and slope efficiencies up to 84.5%. 82 nm tunability range was demonstrated for E//c polarization.

Yb3+:CaYAlO4-based chirped pulse regenerative amplifier.

The results of an experimental study of the chirped pulse amplification regime are reported for the Yb:CaYAlO4 crystal with different polarization states in the gain media for the first time, to the best of our knowledge. A maximum output power of 4.2 W with 310 fs pulse duration was obtained for σ-polarization at 200 kHz repetition rate seeded by a 85 fs Yb:KYW oscillator. 215 fs pulses with an output power of 3 W and 190 fs with 2.3 W output power were demonstrated for π-polarized light in the crystal. Gain narrowing effects for different polarization states in the crystal are discussed.

200 kHz 5.5 W Yb(3+): YVO4-based chirped-pulse regenerative amplifier.

A chirped-pulse regenerative amplifier based on a Yb:YVO4 (Yb:YVO) crystal was demonstrated for the first time, to our knowledge. A novel wavelength-independent off-axis technique was used to deliver 26.6 W of pump power with a low quantum defect. It was seeded by means of a 120 fs Yb:YVO4 oscillator. It generates as much as 5.5 W of average output power with chirped pulses and 4.2 W with 200 fs compressed pulses at a 200 kHz repetition rate. A maximum pulse energy of 140 µJ was obtained at pulse repetition frequencies up to 25 kHz at the central wavelength of 1018 nm.

Spectroscopy and femtosecond laser performance of Yb3+:YAlO3 crystal.

We report what we believe to be the first demonstration of cw and passively mode-locked Yb(3+):YAlO(3) (Yb:YAP) laser operation under diode pumping. Spectroscopic properties of a 0.6 at.%Yb(3+)-doped YAP single crystal were investigated. Output power up to 1.2 W with slope efficiency of 64.5% in the cw regime and 225 fs pulse duration with average power of 0.8 W from a mode-locked Yb:YAP laser were demonstrated.