Cr:YAG crystal is a solid state laser active material broadly tuneable in the near infrared spectral region (1.35 - 1.57 um) which makes it attractive for applications in optical fiber communications, laser remote sensing, eye-safe ranging and numerous other uses. Its broad absorption band offers a variety of possible pump sources including Nd:YAG lasers and InGaAs diode lasers. The usefulness of Cr:YAG as an active laser material was rapidly demonstrated [1]. At present the trend is directed to development of compact self-mode-locked Cr:YAG lasers as perspective sources of femtosecond pulses in the 1.55 um telecommunication band[2].

In our previous paper we reported about continuous generation in Cr:YAG laser with symmetrical four mirror folded resonator with spherical mirrors having radii of curvature of 100 mm [3]. The lowest threshold for continuous operation was 2.8 W of absorbed pump power from arc lamp excited in house built continuous Nd:YAG laser generating linearly polarised radiation at wavelength of 1.06 um in single transversal mode. It was possible to adjust self-mode-locked regime in this laser by inserting a vertical slit into the resonator close to the flat end mirror and by changing the positions of the curved folding mirrors. The main problem in this experiment was the low temporal and pointing stability of pump laser.

In this paper we present results of optimisation of resonator parameters of pump laser in order to obtain dynamically stable configuration insensitive to variations of focal length of thermal lens created in Nd:YAG crystal and small misalignment of mirrors. Results of experimental verification of improved stability will be reported. The second part contains results of computer analysis of three mirror astigmatically compensated resonator of Cr:YAG laser consisting of two spherical mirrors and flat output mirrors. Using optimised compact three mirror resonator with mirrors having radii of curvatures of 75 mm the Cr:YAG laser threshold was decreased to 1.5 W of absorbed pump power. For absorbed pump power of 3 W the output power in single beam extracted through one curved mirror with reflectivity of 99.8% was 30 mW and total extracted power through all three mirrors was more than 100 mW at wavelength of 1.45 um. These data confirm a good potential of developed Cr:YAG laser for pumping by a laser diode excited solid state laser with a moderate power 3-4 W.

References

[2] Valentine,G.J. - Sibbett,W.: Proceedigs of Conference on Lasers and Electro-Optics CLEO 98 pp162-163, paper CTuM47, OSA 1998

[3] Kubeček,V. - Jelínková,H. - Takagi,Y. - Agnesi,A.: 3rd Int. Conference PHOTONICS 99, Prague SPIE Proceedings Vol. 4016, January 2000

This research has been supported by GACR grant No. 102/97/0580 and by MSMT grant J04/98:210000022

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