Which of the Following Is Essential for Laser Action to Occur

question 3

Multiple Choice

Which of the following is essential for laser action to occur between two energy levels of an atom?

• A)the lower level is metastable
• B)the upper level is metastable
• C)the lower level is the ground state
• D)the are more atoms in the lower level than in the upper level
• E)the lasing material is a gas

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