laissez-passer vs safe conduct

laissez-passer

noun
  • A pass or permit; a document permitting the bearer to travel, sometimes issued as an emergency passport. 

safe conduct

noun
  • The security given by authority of a government to a stranger for his quietly coming into and passing out of the territories over which said government has jurisdiction or control. 

How often have the words laissez-passer and safe conduct occurred in a corpus of books? (source: Google Ngram Viewer )