Passive Q-switching of ∼2.7 µm Er:Lu₂O₃ceramic laser with a semiconductor saturable absorber mirror

Abstract

We demonstrate the passively Q-switched operation of an Er:Lu 2 O 3 ceramic laser at >2.7 µm for the first time, to the best of our knowledge. By using a semiconductor saturable absorber mirror (SESAM), stable pulse trains with a repetition rate of 20-33.3 kHz are produced in a compacted v-shaped resonator. The pulse duration (FWHM), pulse energy, and peak power are 660 ns, 1.8 µJ, and >2.73 W, respectively, at 33.3 kHz repetition rate. Prospects for further improvements in terms of laser performances are discussed.

High Power and Short Pulse Width Operation of Passively Q-Switched Er:Lu2O3 Ceramic Laser at 2.7 μm

“…The Er:Lu 2 O 3 ceramic laser in present work provides similar pulse energy and average output power to the crystal laser, but higher pulse peak power and five times decrease in pulse duration [21][22][23]29]. Compared to the earlier reported PSQ Er:Lu 2 O 3 ceramic laser at 2.7 µm, the average output power and slope efficiency in the present work have increased by nearly an order of magnitude [29].…”

“…The measured pulse duration and the pulse repetition rate as a function of the absorbed pump power are presented in Figure 3. The pulse duration was 81 ns near the threshold and shows a slight decrease with an increase in the absorbed pump power, while the repetition rate monotonically increased from 3.1 kHz to 71 kHz as the absorbed pump power varied from 2.3 W to 9.4 W. At an absorbed pump power of 9.4 W, the minimum pulse width of 70 ns was obtained, which is nearly an order of magnitude narrower than previously reported for the PSQ Er:Lu 2 O 3 ceramic laser [29]. Given that the PSQ laser properties related to the SA, the improved performance in the present work can be attributed to the following reasons: low non-saturable loss of the Bragg-reflector-based SESAM itself results in a higher laser gain, while matching the semiconductor band-gap energy with the lasing photon energy further decreases the saturation fluence and the saturation carrier density of the SA, and thus, bleaching the SA is achievable with fewer laser photons, which in turn results in a decreased intracavity loss and an increased laser net gain [30,31].…”

“…The Er:Lu 2 O 3 ceramic laser in present work provides similar pulse energy and average output power to the crystal laser, but higher pulse peak power and five times decrease in pulse duration [21][22][23]29]. Compared to the earlier reported PSQ Er:Lu 2 O 3 ceramic laser at 2.7 µm, the average output power and slope efficiency in the present work have increased by nearly an order of magnitude [29]. This can be attributed to the modified cavity structure with increased utilization efficiency for the pump power, together with the optimized SA parameters with a decreased intracavity insertion loss.…”

“…In general, metal-reflector-based SESAMs have a relatively high non-saturable loss of >5% induced by the included buffer layer, substrate and Au bottom mirror, and hence may limit the performance of 3-µm solid-state lasers [27,28]. Q-switched operation of Er:Lu 2 O 3 ceramic laser using metal-reflector-based absorber has very recently been demonstrated, generating 60 mW of average output power with 660 ns of pulse duration [29].…”

Modeling of end-pumped electrooptically Q-switched lasers with the influences of thermal effects and spatial mode matching

“…In previous studies, spatial mode matching between the pump and lasing modes along the gain medium has been confirmed to be of great importance in determining output parameters. [10][11][12][13] However, serious thermal effects such as the thermal lens effect and thermally induced diffraction loss significantly affect the lasing mode size within the cavity, leading to the weakening of the pulse energy and the decrease in the pulse width, [14][15][16][17] which is not accurate with the exclusion of spatial mode matching with thermal effects at high pump levels. Clearly, a theoretical model, including spatial mode size and thermal effects, is required for predicting high-power end-pumped actively Q-switched (AQS) lasers with high accuracy.…”