What is a characteristic of semiconductor diode lasers?

Semiconductor diode lasers are characterized by their ability to emit a fan-shaped beam. This is primarily due to the structure of the laser itself, which typically has a narrow output aperture designed to produce a beam that spreads out in a specific pattern. The fan-shaped beam is advantageous in a variety of applications because it allows for a wider area of illumination or data transmission.

The other options do not accurately reflect the characteristics of semiconductor diode lasers. While laser safety is important and considerations about carcinogenic properties are relevant in the context of certain laser types, semiconductor diode lasers are not predominantly known for being highly carcinogenic. The assertion that they are only used in industrial settings is not accurate, as these lasers also have widespread applications in consumer electronics, telecommunications, and medical devices. Finally, semiconductor diode lasers are capable of emitting light across a broad spectrum, not just red; they can produce various wavelengths, including infrared, green, and blue, depending on the materials used in their construction.