DPAL laser with local bidirectional alternative flowing gain medium

The invention provides a DPAL laser with local bidirectional alternative flowing gain medium. The DPAL laser comprises a steam box, an alkali metal generating device, an alkali metal recovery device, a circulation sub-system, a pumping module and a resonant module, wherein the alkali metal steam of the DPAL laser only flows in local, thus only the area adjacent to the steam box needs to maintain relative high temperature, the other areas can be at room temperature, and the requirement on the vacuum heat resistant performance of the laser is greatly reduced; as the alkali metal steam with very active chemical property is limited to be adjacent to the steam box, the alkali metal steam is prevented from being consumed by reaction between the alkali metal steam and a pipeline and components in the pipeline, and the pipeline and a fan do not need to be exposed under the high-temperature environment and are prevented from contacting the alkali metal steam, thus the pollution to the air channel and the cavity caused