Dear Professor XXXXXX,
How is everything going on recently? I am writing to inquire if you can send me the official invitation letter. The official invitation letter should use special letter paper of the Institute of Physics. You can send it to me directly in a scan version. A draft of acceptance letter in word format and a model in JPEG format are affiliated in the email. Together with the official invitation letter, you can send the research plan and your CV with your signature together. I will be very glad to hear from you.
With my best regards,
Yours Sincerely,
XXXXXXX