FYI. Here is my sample emails for requesting reference letter.
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Dear Professor XXXX:
My name is XXXX and I’m a Research Associate at the University of NoWhere. My research is focused on XXXX, XXX. I have been an active reviewer for several important IEEE transactions in my field.
I have always enjoyed reading your articles on XXXXX; I have followed your publications closely during past several years. Based on the analysis results of your paper, I have developed several new algorithms to solve XXX problems. Some of the results have been presented at different IEEE conferences and published on IEEE Trans. on XXX.
I am in the process of applying for a permanent resident visa (I-40, green card), and I need to find some independent experts to comment on my work in the form of 1~2 pages of letter. According to U.S. Citizenship and Immigration Service (USCIS), independent experts are defined as people who either do not know the beneficiary / applicant personally or have never worked with the applicant.
You are a top national expert in our field and therefore best person to write such a letter for me. Could you favor me with this reference letter? I understand that you are such a busy professor; therefore, I want to make sure it will cost you less than one or half hour. To achieve that, I will provide you with a detailed template letter according to guidance given by my attorney, if it is OK with you.
Please visit my website to get more information about my work,
http://students.myuniversity.edu/yourname
I will provide you with my detailed Curriculum Vitae later.
I sincerely appreciate your time and kind help.