What are the wavelength and type of the laser used in a standard CD-ROM drive?

Question

Question

This question was previously asked in

RRB NTPC Graduate Level CBT-I Official Paper (Held On: 09 Jun, 2025 Shift 1)

Answer 1

The correct answer is 780 nm; infrared laser.

Key Points

Standard CD-ROM drives use infrared lasers with a wavelength of 780 nm to read data encoded on the discs.
The laser interacts with the reflective surface of the CD, detecting pits and lands that represent binary data.
The 780 nm wavelength is optimal for CDs due to the size of the pits and the design of the disc structure.
Infrared lasers are not visible to the human eye but are highly effective for reading older optical media formats such as CDs.
Other optical storage devices like DVDs and Blu-ray discs use lasers with shorter wavelengths, enabling higher data storage capacities.

Additional Information

Laser Wavelengths in Optical Media:
- DVDs: Use red lasers with a wavelength of approximately 650 nm, allowing higher data density compared to CDs.
- Blu-ray discs: Use blue lasers with a wavelength of 405 nm, enabling even greater storage capacity due to smaller pits.
Working Principle of Optical Drives:
- Data is stored on optical discs in the form of microscopic pits and lands.
- The laser beam reads these patterns by detecting changes in reflectivity.
- The reflected signal is converted into electrical signals, which are interpreted as binary data.
Infrared Radiation:
- Infrared radiation is electromagnetic radiation with wavelengths longer than visible light but shorter than microwaves.
- It is widely used in communication devices, remote controls, and optical media systems.
Evolution of Optical Media:
- CDs were introduced in the 1980s as a digital replacement for analog audio storage.
- DVDs and Blu-ray discs followed, offering higher capacities for video and data storage.
- With the advent of solid-state drives (SSDs) and cloud storage, optical media usage has significantly declined.