It seems like the answer options are missing from your query. A common example of a four-level laser is a Nd:YAG laser. Other examples include He-Ne lasers.
Which of the following is a four-level laser?
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Question context
This question is part of ⚡ Electrical Engineering within the broader 🛠️ Engineering Essentials subject and appears in the SPSC – Sindh Public Service Commission preparation collection. Reviewing the answer together with nearby questions helps reinforce the underlying concept and identify how it may appear in competitive exams.