ANS:D - a beam of coherent light.

Laser is a device to produce a beam of coherent light. Explanation:

1. Gamma rays: Gamma rays are a form of electromagnetic radiation with very short wavelengths and high frequencies. Lasers do not produce gamma rays.
2. Microwaves: Microwaves are also a form of electromagnetic radiation, with longer wavelengths and lower frequencies compared to visible light. Lasers do not produce microwaves.
3. A beam of white light: While some light sources, such as incandescent bulbs or the sun, emit white light, lasers do not produce white light. Instead, lasers emit light of a specific wavelength, typically in the visible, infrared, or ultraviolet spectrum.
4. A beam of coherent light: Coherent light refers to light waves that are in phase with each other, meaning they have the same frequency and direction. Lasers produce coherent light by stimulating the emission of photons in a process called stimulated emission. This results in a highly directional, monochromatic (single-color), and coherent beam of light. This unique property of lasers makes them useful in a wide range of applications, including communications, manufacturing, medicine, and research.