A double pass $Nd^{3+}$ liquid amplifier and a $Nd^{3+}$:glass oscillator, both containing a stimulated Brillouin scattering(SBS) mirror, were constructed and their characteristics were investigated.
To achieve good SBS reflectivity, the effect of the purity of SBS medium on SBS reflectivity was investigated. In this experiment, 0.2 μm filter was used to remove the impurity in the FC-72 SBS medium. As a result, the reflectivity could be obtained up to 96% of the input laser energy. The breakdown threshold was increased by three times.
For the double-pass $Nd^{3+}$ liquid amplifier with SBS mirror, a $Nd^{3+}:POCl_3-SnCl_4$ solution was prepared as a laser gain medium. The spectral and lasing characteristics of liquid laser materials based on $POCl_3$ as inorganic solvents activated with $Nd^{3+}$ are comparable to those of $Nd^{3+}$ doped crystals and glasses. Two schemes for the double-pass $Nd^{3+}$ liquid amplifier with SBS mirror were investigated. One is well known scheme which consists of laser amplifier and SBS cell. The other is very simple scheme which consists of only a $Nd^{3+}$ liquid amplifier. In second scheme, the input beam was focused into the laser gain medium so that the reflection by SBS of liquid host material($POCl_3-SnCl_4$) and amplification by the excited Nd ion occurs simultaneously in the $Nd^{3+}$ liquid amplifier. The wavefront distortion, however, could not be compensated due to severe polarization distortion by thermal birefringence in liquid laser medium.
A simple method to improve the spatial profile of a passive Q-switched $Nd^{3+}$:glass laser(PQL) was proposed. To smooth the output profile, the passive Q-switched $Nd^{3+}$:glass laser utilized an auxiliary SBS output coupler. The spatial profile of such laser was significantly improved, the focusibility resulting in better. This laser showed several merits. First, the pulse width could be easily varied by adjusting the auxiliary cavity length without severe alignment. Second, the single-pulse regime of PQL becomes twice wider when PQL is coupled to the SBS cell. The enlargement of the single-pulse regime are due to the enhanced inversion depletion by the reflection from the SBS cell when the output energy of PQL exceeds the SBS threshold. Futhermore, the output energy was very enhanced by several times compared to PQL. The enhancement of the output energy by SBS cell was demonstrated by using several SBS materials such as acetone, $CS_2$, FC-72 and $SF_6$. This technique to adopt the auxiliary SBS output coupler can be well utilized in wide applications when good spatial beam quality is required.
