P$.3$ATi:$A{l}_2{O}_3$ laser is longitudinally pumped by the focused beam of an $Ar+$ laser at the pump wavelength ${}_p=514nm.$ A wavelength tuner is inserted in the cavity, forcing the laser to oscillate at $850$ nm $.$ Assume a round trip loss of the cavity ${}_{rt}=10\%,$ an output mirror reflectivity $R=95\%,$ and a pump efficiency ${}_p=30\%.$ Assume also that the laser is under optimum pumping conditions. Calculate the laser slope efficiency. $(5$ points$)$