Full length articleCompact diode-pumped continuous-wave and passively Q-switched Nd:GYSO laser at 1.07 µm
Introduction
During the past decades, various Nd3+ lasers producing laser emissions at near infrared spectral domains (0.9, 1.06, 1.1, 1.3 and 1.4 µm) and doped into different host materials of the Nd3+ ion have been greatly developed because these Nd3+ lasers have various important applications. For instance, as one of the most important application, by nonlinear frequency conversion (mainly second-harmonic generation and sum-frequency mixing) with the aid of nonlinear crystals, these Nd3+ infrared lasers can be efficiently wavelength converted to visible lasers at blue [1], [2], green [3], yellow [4], orange [5] and red [6].
Compared with those conventional Nd3+ single crystal laser materials, such as Nd:YAG [7], [8], [9], Nd:GGG [10], [11], Nd:YVO4 [12], [13], Nd:GdVO4 [14], Nd:YLF [15], [16], and Nd:YAP [17], [18], in recent years, laser host materials possessing broad bandwidth have attracted more and more research interest because these broad bandwidth laser materials provides opportunity to pursue ultrashort pulse lasers. According to Ref. [19], such broad bandwidth resulting from an inhomogeneous broadening behavior is attributed to the multiple substitutional sites with low symmetry enhancing the structural disorder to a certain extent. Among disorder laser materials, GYSO showing a combined benefits of the energy splitting from GSO with the more rigid and isotropic structure of YSO gains more and more attention [19]. In fact, in recent years, laser operation of Yb3+-doped GYSO material has been explored thoroughly [20], [21], [22]. However, so far, research on CW Nd:GYSO laser is still very limited. Li et al. [19] reported a maximum 1.54 W laser output with slope efficiency of about 27.4% at 1074 nm. Feng et al. [23] improved the output power and slope efficiency to 3.5 W and 31.8%, respectively. However, the laser emission was still limited to around the 1074 nm line. Laser emissions at other lines and the characteristic of wavelength tuning benefiting from the broad fluorescence of Nd:GYSO crystal have not yet been reported to date.
On the other hand, during the past decade, various 2D nanosheet materials have been developed to act as saturable absorbers (SAs) for Q-switching and mode locking in the fields of solid-state lasers and fiber lasers. These 2D SA materials, such as graphene [24], [25], topological insulator [15], [26], MoS2 [27], [28], [29] and recently created black phosphorus [30], are more and more popular because of their ultra-broadband saturable absorption, low cost and easy fabrication. All these properties lead to such kind of 2D nanosheet materials suitable for mass production not only in the application of SAs but also in various other applications in optoelectronics. MoS2 exhibiting better saturable absorption response than graphene has been successfully used to Q-switch Nd3+ lasers previously [28], [29]. However, at present, MoS2-based Nd3+ Q-switched lasers are still power limited. For instance, in 2014, using MoS2 as saturable absorber, Wang et al. [29] first reported a Nd:GdVO4 Q-switched laser operation at 1.06 µm with pulse width of 970 ns, maximum pulse energy of 0.31 μJ and maximum output power of 227 mW. We recently also reported a MoS2-based Q-switched laser operation at 1079 nm in a Nd:YAlO3 laser cavity. Although the pulse energy was as high as 1.11 μJ benefiting from the short pulse width as 227 ns, the maximum output power was still limited to be 0.26 W [28].
In this work, we present a power and efficiency scaling of a diode-pumped Nd:GYSO laser operating at 1074 nm. The first laser operation at 1058 nm from this crystal is also obtained in free-running mode. Moreover, wavelength tuning is also fulfilled by using a thin etalon. Finally, using MoS2 SA, a stable Q-switched Nd:GYSO laser can also be realized.
Section snippets
Experimental setup
The laser system consisted of three parts, which is schematically shown in Fig. 1. Firstly, the laser gain medium was a 0.5 at% doped Nd:GYSO crystal with dimensions of 3×3×8 mm3 (8 mm in length), which was grown by the Czochralski method. The details on the crystal growth can be found in Ref. [19]. The laser crystal was wrapped in indium foil and then mounted into a copper holder. The copper holder was connected to circular cooling water with temperature controlled at 18 °C to remove the thermal
Results and discussion
The maximum absorption ratio of the laser crystal was found to be about 73% at maximum pump power, which indicated that maximum absorbed pump power was about 9.65 W. CW laser experiments in free-running mode were fulfilled by using several different output mirrors and the data is shown in Fig. 2, Fig. 3. Fig. 2 shows the laser emission at 1074 nm and four output mirrors (TOC1, TOC2, TOC3, TOC4) were used during the experiments. Among these mirrors, TOC1, TOC2 and TOC3 have radii of curvatures of
Summary
In this work, diode-pumped Nd:GYSO lasers have been studies in CW and Q-switched modes by using a compact two-mirror laser cavity. In CW free-running mode, maximum output power up to 4.1 W was achieved at 1074.11 nm with maximum slope efficiency of 48.5%, which presented the best laser performance for this crystal at present, to the best of our knowledge. By using a different output mirror with coating favoring the 1059 nm lasing, a CW free-running 1058.27 nm laser can also be firstly generated
Acknowledgement
The authors wish to thank the financial support from National Natural Science Foundation of China (51302285, 61522510, and 61575164), the Specialized Research Fund for the Doctoral Program of Higher Education (20130121120043), the Fundamental Research Funds for the Central Universities (2013121022), External Cooperation Program of BIC, CAS (No. 181231KYSB20130007) and Natural Science Foundation of Fujian Province of China (2014J01251).
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