Did Isaiah know he was writing about the crucifixion?
No, Isaiah did not know or picture the crucifixion as he wrote Isaiah 53. God had him write it so that after the fact people could look back and see the work of the cross, especially for the benefit of the Jew.
Les explains that Isaiah 53 is a prophetic statement concerning the work of the cross, but Isaiah did not understand or envision the crucifixion as he wrote it. Although many claim Old Testament believers saw the cross in the future, Les says they did not. Instead, God had Isaiah write it so that after the fact, people—especially the Jew—could go back to Isaiah 53 and see that God had the work of the cross in mind all along.
Surely he hath borne our griefs, and carried our sorrows: yet we did esteem him stricken, smitten of God, and afflicted.