Abstract
We report a comprehensive design procedure for passively $Q$-switched monolithic $\text{Nd}{:}\text{YAG}/{\text{Cr}^{4 + }}{:}\text{YAG}$ microchip lasers to realize operation conditions of the pulse repetition rate (PRR) ${ \gt } 100 \;\text{kHz}$ and pulse width (PW) ${ \lt }\, 400 \;\text{ps}$, simultaneously. Crucial parameters including effective pump power and waist diameter of the pump laser, doping concentration and thickness of the Nd:YAG crystal, initial transmittance (${T_0}$) of the ${\text{Cr}^{4 + }}{:}\text{YAG}$ crystal, as well as the reflectivity of the output coupler are all considered during the design process. Two single-longitudinal-mode-operated lasers are designed and constructed according to the numerical results. The lengths and doping concentrations of Nd:YAG for both microchips are optimized to be 0.5 mm and 2%, respectively. A PRR up to 170 kHz and PW of $\sim 370\;\text{ps}$ are measured under the pump power of 2.6 W for a microchip with ${T_0}$ of 0.85. A slightly lower PRR of 118 kHz with a shorter PW of ${\sim} 320 \;\text{ps}$ is also achieved under the same pump power for another microchip with ${T_0}$ of 0.8. The related pulse energies for the two microchips are ${\sim} 2.1 \;\unicode{x00B5} \text{J}$ and ${\sim} 1.8 \;\unicode{x00B5} \text{J}$, respectively. To the best of our knowledge, these results are among the highest PRRs achieved for passively $Q$-switched $\text{Nd}{:}\text{YAG}/{\text{Cr}^{4 + }}{:}\text{YAG}$ microchips with PWs ${ \lt }400\;\text{ps}$.
© 2020 Optical Society of America
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