107509
For FDML operation , the filter tuning frequency f needs to match the inverse cavity roundtrip time 1 / \ tau = c/L or a i-th harmonic thereof , with the group speed of light c in the cavity .
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Please list all entity words in the text that fit the category. Output format is "word1, word2". 
Option: location, person, organization 
Text: {0} 
Answer:
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