Diode-pumped 671nm laser frequency doubled by CPM LBO

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Abstract

A design of diode-pumped high-efficiency Nd:YVO4/LBO red laser is reported. Using critical phase-matching (CPM) LBO, 671nm red laser was obtained from 1342nm light by intracavity frequency doubling. With an incident pump laser of 800mW, using type-I and type-II CPM LBO, 97 and 52mWTEM00 mode red laser outputs were obtained, with optical-to-optical conversion efficiencies of up to 12.1% and 6.5%, respectively.

Introduction

It was well known that Nd3+ doped in YVO4 can also emit 1342nm in addition to 1064nm. Furthermore, Nd3+ can have a high doped concentration and emit polarized light in YVO4 [1], so Nd:YVO4 is highly suitable for diode-pumping to generate 1342nm laser, which can be frequency doubled to obtain 671nm red laser.

There are already some papers on diode-pumped 671nm red lasers [2], [3], [4], but all of them used type-II CPM KTP or NCPM LBO to generate the second harmonic wave. Among them, with a fiber-coupled 10W diode array, Zhang et al. used type-II KTP to achieve 671nm output of about 70mW [2]; also Zhang et al. used type-I NCPM LBO (T≈5°C) and a V-shaped folded cavity to obtain 502mW output, with optical-to-optical conversion efficiency up to 8.3% [3]; Agnesi et al. used type-II NCPM LBO (T≈38°C) and a V-shaped folded cavity to obtain 430mW output [4].

Analysis has shown that KTP has a low second harmonic generation (SHG) efficiency and bad beam quality due to its large walk-off angle, while NCPM LBO requires strict temperature control and is very hard to be a commercial product [5], especially for type-II NCPM LBO which has the highest efficiency, however, it strongly requires dry surroundings due to its work temperature being lower than room temperature. As to CPM LBO, we have not found any reports on it for 1342nm frequency doubling in diode-pumped Nd:YVO4 red lasers.

In this paper, type-I and type-II CPM LBO was used for 1342nm intracavity frequency doubling. By reasonable design, high SHG efficiency and good beam quality were obtained.

Section snippets

Characteristics of CPM LBO for 1342nm frequency doubling

We have calculated some important parameters of different CPM crystals. Critical phase-matching angle (θ,φ), effective nonlinear coefficient (deff), walk-off angle (ρ) and acceptance angle of CPM LBO (I), LBO (II) and KTP (II) are listed in Table 1.

Data listed in Table 1 showed that although LBO has less deff than KTP, its little walk-off angle and large acceptance angle can make LBO's effective work length (L) very long for 1342nm frequency-doubling. Based on the formula [6]L=1.16ω/ρ,where ω

Experimental setup

Based on the above analysis, the optional parameters were designed by computer programming. The equipment is shown in Fig. 1.

A laser diode with maximum output 1W, a central emitting wavelength of 806.4nm at 23°C and a divergent angle of 7.2×33.6deg2 was used as the pumping source. After going through the coupling optics, light emitted from the LD was reshaped to high-quality pumping light (with an ellipticity of 0.91, beam waist's radius is about 95μm) and was injected into Nd:YVO4 (1.3mm

Results and discussions

In the same setup, type-I and type-II CPM LBO were used for 1342nm frequency doubling, respectively. After 808 and 1342nm light were filtered, the 671nm laser output power was measured. The red laser's power as a function of pumping light is shown in Fig. 2.

Fig. 2 shows the thresholds of pump power were both about 40mW under the two conditions. But above the threshold, CPM LBO (I) is markedly better than LBO (II). When the pump light of 800mW was injected, 97 and 52mW671nm outputs were obtained

Conclusions

For the first time, type-I and type-II CPM LBO were used for 1342nm intracavity frequency doubling of a Nd:YVO4 laser. By reasonable design, high SHG efficiency and good beam quality were obtained. With 800mW incident pump laser, using type-I and type-II CPM LBO, 97 and 52mWTEM00 mode red laser outputs were obtained, the optical-to-optical conversion efficiencies are up to 12.1% and 6.5%, respectively. Furthermore, the power would be increased by a big margin if a folded cavity was used. We can

Acknowledgements

This work was supported by the National High-tech 863 plan of People's Republic of China (No.863-307-22-51, 863-16-05).

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