I get asked about the best way to send a thank you note after an interview.  These days a simple email is all you need to send. Be sure to send the note within 24 hours of your interview.  The sooner the better. 
Below is a great example (with edits for confidentiality) of one that a candidate of one of my colleagues sent to a client practice.  
Dear Dr. “Smith”,
I just wanted to say thank you for the opportunity to visit with you. Both the interview and the tour made for an exciting and complete day. I was so very impressed with the office tour. You were very thorough in explaining how the practice works and what would be expected when I join the team. I have been on several interviews and none have been as relaxing, stress free, and heartfelt as the one at “ABC Optometry”.
Thank you again for the opportunity to be considered for an Optometrist position at “ABC Optometry.” The interview served to reinforce my strong interest in becoming a member of the practice. I appreciate the chance to visit with you. I look forward to hearing from you again soon. 
Best regards,
Dr. “Jones”
Great note!  Because of this note the doctor is moving quicker through the interview process because the owner knows this candidate has a genuine desire to work for the practice. 

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