Stefano Veronesi

Compact passively Q-switched diode-pumped Tm:LiLuF4 laser with 1.26 mJ output energy.

We demonstrate efficient continuous-wave (CW) and passively Q-switched Tm:LiLuF(4) laser operation near 1.9 μm. The CW slope efficiency reached 54.8% with respect to absorbed power. Stable passive Q-switching with Cr(2+):ZnS saturable absorbers resulted in minimum pulse duration of 7.6 ns and maximum pulse energy and peak power of 1.26 mJ and 166 kW, respectively.

Efficient in-band pumped Ho:LuLiF 4 2 μm laser

An efficient Ho:LuLiF(4) laser in-band pumped by a cladding-pumped Tm-doped silica fiber laser operating at 1937 nm is reported. At low-cavity output coupling, the Ho:LuLiF(4) laser yielded 5.1 W of output at a wavelength of 2066 nm for 8.0 W of absorbed pump power with a slope efficiency of 70%. At high-cavity output coupling, the lasing wavelength shifted to 2053 nm and the laser produced an output power of 5.4 W with a slope efficiency of 76%. The beam propagation factor (M(2)) was measured to be approximately 1.1 at the maximum output power confirming fundamental transverse mode (TEM(oo)) operation. The influence of resonator design on laser performance is discussed, along with prospects for further power scaling and improvement of the laser efficiency.

Passively Q-switched Tm:YLF laser

Stable passive Q-switching of a Tm:  LiYF4 laser is obtained using polycrystalline Cr2+:  ZnS as a saturable absorber. The achieved maximum pulse energy of 0.9 mJ and peak power of 65 kW for a pulse duration of ∼14  ns represent substantial improvement and highest values for a passively Q-switched diode-pumped Tm laser operating at ∼1.9  μm.

Sub-50-fs widely tunable Yb:CaYAlO(4) laser pumped by 400-mW single-mode fiber-coupled laser diode.

Yb:CaYAlO(4) has been investigated spectroscopically and compared to better known Yb:CaGdAlO(4). It turns out that both materials show very similar spectroscopic parameters relevant to ultrafast lasers design. Employing single-mode fiber-coupled 400-mW laser diode at 976 nm we measured pulses as short as 43 fs, and broad tunability of 40 nm with a simple single-prism setup.

GaSb-based SESAM mode-locked Tm:YAG ceramic laser at 2 µm

Tunable and mode-locked laser operation near 2 µm based on different Tm-doped YAG ceramics, 4 at.% and 10 at.%, is demonstrated. Several designs of GaSb-based surface-quantum-well SESAMs are characterized and studied as saturable absorbers for mode-locking. Best mode-locking performance was achieved using an antireflection-coated near-surface quantum-well SESAM, resulting in a pulse duration of ~3 ps and ~150 mW average output power at 89 MHz. All mode-locked Tm:YAG ceramic lasers operated at 2012 nm, with over 133 nm demonstrated tuning for continuous-wave operation.

Prospects of Holmium-doped fluorides as gain media for visible solid state lasers

In this paper we report on the suitability of Ho3+:LiLuF4 and Ho3+:LaF3 as active media for solid state lasers emitting in the green spectral region. The ground state absorption spectra were measured and employed to calculate the emission cross section spectra via the reciprocity method. These allowed to derive the gain characteristics for various inversion ratios. The decay dynamics of the 5F4,5S2 multiplet, which would act as upper laser level, were investigated to estimate the quantum efficiency. Measurements of the excited state absorption were conducted which showed that stimulated emission is the dominating effect around 550 nm. Laser operation was demonstrated in the green spectral region by employing Ho3+:LaF3 as gain medium. Laser oscillation occurred in a self-pulsed regime with a maximum average output power of 7.7 mW, a repetition rate of 5.3 kHz, and a pulse duration of 1.6 μs. To the best of our knowledge this constitutes the first green laser emission of a Ho3+-doped crystal at room temperature.

Optical spectroscopy of Tm3+?:?YAG transparent ceramics

Transparent YAG ceramics doped with different concentrations of Tm3+ have been fabricated by solid state reactive sintering and their spectroscopic properties have been thoroughly investigated. Absorption, emission and fluorescence decay measurements have been carried out in different experimental conditions in order to obtain information about the radiative and non-radiative processes in these materials. The 2 µm stimulated emission performance has been evaluated using for the first time an astigmatically compensated cavity which permitted assessment of the tunability of the laser emission.

Efficient laser emission in Ho 3+ :LiLuF 4 grown by micro-Pulling Down method

We report a spectroscopic investigation and an efficient Ho:LiLuF4 laser in-band pumped at 1938 nm. This represents the first laser emission of a fluoride crystal grown by micro-Pulling Down method in the 2 μm wavelength range. The Ho:LiLuF4 laser yielded a maximum output power of 7.1W with a slope efficiency of 41% and a threshold around 5W, at lasing wavelength of 2054.2 nm.

In-band pumped Ho 3+ :KY 3 F 10 2 μm laser

A maximum laser power of 2.4 W was obtained at a wavelength of ~ 2040 nm for 23 W of absorbed pump power with a slope efficiency of 21.6 % with respect to absorbed power.

Comparative spectroscopic and thermo-optic study of Tm:LiLnF 4 (Ln = Y, Gd, and Lu) crystals for highly-efficient microchip lasers at ~2 μm

We report on a detailed comparative study of the spectroscopic and thermo-optic properties of tetragonal Tm:LiLnF4 (Ln = Y, Gd, and Lu) crystals indicating their suitability for highly-efficient microchip lasers diode-pumped at ~791 nm and operating at ~1.91 μm. An a-cut 8 at.% Tm:LiYF4 micro-laser generated 3.1 W of linearly polarized output at 1904 nm with a slope efficiency of η = 72% and a laser threshold of only 0.24 W. The internal loss for this crystal is as low as 0.0011 cm−1. For 8 at.% Tm:LiGdF4 and 12 at.% Tm:LiLuF4 lasers, the output power reached ~2 W and η was 65% and 52%, respectively. The thermal lens in all Tm:LiLnF4 crystals is weak, positive and low-astigmatic. The potential for the Tm:LiLnF4 lasers to operate beyond ~2 μm due to a vibronic coupling has been proved. The Tm:LiYF4 vibronic laser generated 375 mW at 2026-2044 nm with η = 31%. The Tm:LiLnF4 crystals are very promising for passively Q-switched microchip lasers.