Dear Friends:
Can any one of you have time to explain the tense in the following sentence:
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A beam of coherent light one-half inch wide will be three inches wide after
it has travelled one mile.
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In the adverbial clause, present perfect tense is used. But, this kind of
tense is generally used for an action which has finished so far. I think we
should use future perfect tense because it will be finished after it travels
one mile. Am I right?

Secondly, In English, all the words have one or more attribution. For
example, the word "mail" can be a noun, an transitive verb. Then, what about
"to" when it is used as an indicator of infinitive or infinitive phrases?
What does it belong to ?

TIA

Tianyi