Abstract

In this work we report on the generation of third-harmonic 120 µW average power light at 440 nm in bulk GeO₂-SiO₂ and Er³⁺-doped GeO₂-SiO₂ glasses pumped by a Nd:YAG at 1.319 pm. In the experiment, a Nd:YAG laser operated at 1.319 µm was employed as the pump source. The laser delivered 150 ps pulses at 100 MHz repetition rate in a 700 ns Q-switch envelope at 1 kHz frequency. Our investigations were performed utilizing optical fiber preform samples. The preforms had both germanosilicate core and Er³⁺-doped germanosilicate core. Figure 1 shows a typical power spectrum of the third-harmonic signal at 440 nm generated in a 2 mm thick sample of 8% GeO₂ - doped silica optical fiber preform, for an average pump power of 400 mW. The light at 440 nm was the unique visible signal observed in the spectral region of 400 - 700 nm and was generated instantaneously with pump light illumination. The signal was generated in bursts of Gaussian shaped Q-switch envelopes of ~ 400 ns duration and the individual modelocked picosecond pulses in the envelope could also be observed. The pump power dependence of the output visible signal was investigated and presented a cubic power law dependence with pump intensity as expected for a parametric third-harmonic generation process. For the highest average pump power available, as much as 120 µW average power of blue-violet light at 440 nm was generated, corresponding to peak pulse powers of ~ 0.2 W. We have also tested, Er³⁺- doped germanosilicate fiber performs samples and the third-harmonic power spectrum has essentially shown the same characteristics as the undoped samples. However, in contrast to undoped samples, the signal intensity dependence with pump power for Er³⁺-doped glasses, has shown an initial cubic dependence for low powers and fourth order for intermediate powers, as illustrated in graph of Fig.2. For high pump powers an exponential growth was observed. This behavior is attributed to two and three-photon ressonance enhancement of χ⁽³⁾ [1, 2].

© 1996 IEEE