Diode-pumped alkali vapor laser (DPAL) is a candidate in high power laser field. Under conditions of high-power pumping, ionization process will occur in DPAL′s gain medium, which has a negative impact on laser performance. One of the main rubidium atomic ionization channel is cascaded effect (5S→5P→5D) induced by the 776 nm far wing spectral component of the 780 nm diode pump source. In order to quantitatively measure the degree of ionization of rubidium DPAL, frequency-narrowed 776 nm high power semiconductor light source is needed to simulate the far wing of 780 nm pump light. Based on Littrow configuration, a linenarrowed 776 nm semiconductor laser output is realized, with spectral linewidth of less than 0.15 nm, output power of more than 10 W, and external cavity efficiency of 67%. By using 780 nm and 776 nm cascade pumping, a significant enhancement of fluorescence signal has been observed.