LED vs. LASER: Which Properties Are Superior for a LASER Source? Consider the statements comparing a LASER source with an LED: Higher emission efficiency. No tuning arrangement. Narrow spectral width. Provision for optical confinement. Which statements are correct for a typical LASER relative to a typical LED?

Introduction / Context:
Semiconductor LEDs and LASER diodes are both widely used optical sources. However, they differ fundamentally in emission mechanism and optical characteristics, which drives their use in communications, sensing, and illumination.

Given Data / Assumptions:

• Typical edge-emitting or VCSEL-type LASER diodes versus common LEDs.
• Comparison at similar emission wavelengths.
• General properties rather than specific niche devices.

Concept / Approach:

LASERs provide stimulated emission with optical feedback, producing a coherent, narrow spectral line (small Δλ) and strong optical confinement in a cavity and waveguide. LEDs emit by spontaneous recombination over a broader spectrum and generally lower external efficiency into a given optical mode.

Step-by-Step Solution:

Verification / Alternative check:

Datasheets and textbooks show LED spectral widths of tens of nanometers versus LASER linewidths from sub-nanometer to much narrower; also, coherent beam quality and coupling efficiencies are higher for LASERs.

Why Other Options Are Wrong:

Any option including statement 2 is invalid because LASERs indeed can be tuned or include provision for tuning.

Common Pitfalls:

Assuming “efficiency” only means radiant flux per electrical watt without considering coupling into an optical mode; LASERs excel at delivering power into single-mode fibers.

Final Answer:

1, 3, 4 are correct