We report the spectroscopy and high-power continuous-wave (CW) diode-pumped laser operation of Er: Yb: YAl 3 ͑BO 3 ͒ 4 crystal. Absorption and stimulated emission spectra, emission lifetimes, and efficiency of energy transfer from Yb 3+ level lifetime minimizes excited state absorption and upconversion losses, whereas the high luminescence quantum yield from the 4 I 13/2 level provides high laser efficiency. However, glasses suffer from low thermal and mechanical stability that limits the laser power to the level of a few hundred milliwatts due to the thermal lensing effects and optical damage of the active element. This is why the search for an efficient crystalline host for Er doping is of high interest.CW room-temperature 1. [7].YAl 3 ͑BO 3 ͒ 4 crystal is a well-known laser host for Yb and Nd ions [8,9]. For Er-doped YAB, only crystal growth [10], some spectroscopic properties [11,12], and quasi-CW lasing with average output power of about 40 mW were reported in [13]. In this Letter we report the spectroscopy and for the first time to our knowledge high-power CW laser operation of a diodepumped Er: Yb: YAl 3 ͑BO 3 ͒ 4 laser crystal.Er, Yb: YAB crystals with size of 8 mmϫ 8 mm ϫ 12 mm were obtained by dipping seeded hightemperature solution growth at a cooling rate of 0.2°C-5°C per day in the temperature range of 1060°C -1000°C using K 2 Mo 3 O 10 -based flux [14]. The concentrations of the dopants were measured by microprobe analysis to be 6 ϫ 10 20 cm −3 ͑11 at.% ͒ for Yb 3+ and 0.825ϫ 10 20 cm −3 ͑1.5 at.% ͒ for Er 3+ . The polarized absorption spectra of Er, Yb: YAB crystal measured in the 900-1050 nm range at room temperature are shown in Fig. 1. The spectral resolution was 0.4 nm. The Yb 2 F 7/2 → 2 F 5/2 absorption band in polarization is comparatively broad (17 nm FWHM) with a maximum absorption cross section of about 2.75ϫ 10 −20 cm 2 at 976 nm. In polarization it is considerably weaker (less than 0.3ϫ 10 −20 cm 2 ). Figure 2 shows the accurate absorption spectra of Er, Yb: YAB crystal at 1.45-1.65 m ( 4 I 15/2 → 4 I 13/2 transition of Er). In this spectral range the peaks of the -polarized spectrum are generally higher than those of the -polarized spectrum. The strongest peak with a cross section of 2.75ϫ 10 −20 cm 2 is located at 1531 nm.For lifetime measurements Er͑2 at.% ͒ : YAB crystal was excited by a Nd: YAG pulse-pumped optical parametric oscillator tuned to 976 nm. Excitation pulse duration was about 20 ns. The fluorescence decay was detected using a 0.3 m monochromator, pho- Fig. 1. Room-temperature polarized absorption spectra of Er, Yb: YAB crystal at 1 m.

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We demonstrate, for the first time to our knowledge, femtosecond-regime mode locking of a Tm,Ho-codoped crystalline laser operating in the 2 microm spectral region. Transform-limited 570 fs pulses were generated at 2055 nm by a Tm,Ho:KY(WO(4))(2) laser that produced an average output power of 130 mW at a pulse repetition frequency of 118 MHz. Mode locking was achieved using an ion-implanted InGaAsSb quantum-well-based semiconductor saturable absorber mirror.

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We present a novel variation of the pulsed laser deposition (PLD) technique, aimed at reducing the number of particulates produced and consequently the linear propagation loss observed in the resulting crystal waveguides. The approach relies upon configuring the system to effectively provide bi-directional ablation, whereby the incidence angle of the fixed pulsed laser beam with respect to the target surface changes sign, depending upon the rotation angle and position of the target. Such an alternating ablation direction is intended to reduce the buildup of undesirable periodic surface structures, such as directional cones, believed to be a major source of particulates within the growing film while keeping the plume stationary with respect to the substrate. We show that targets ablated using this technique have fewer directional structures and a decreased surface roughness. Furthermore, using PLD-grown Y 3 Ga 5 O 12 as the exemplar crystal film, we compare growths with uni-and bi-directional ablation and demonstrate reduction from ~ 0.9 to ~ 0.23 dB/cm in the average waveguide propagation losses via the latter.