What changes have taken place in Ai Qing's Selected Poems from the perspective of time?

Poetic style: Before liberation, Ai Qing cursed the darkness and eulogized the light with deep, intense and unrestrained brushwork; After the founding of the People's Republic of China, he continued to praise the people, praise the light and think about life. His "Return" songs are more extensive in content, deeper in thought, deeper in emotion, more diverse in techniques and more sophisticated in art.