- 2080 Baisakh · 3 marks
Short note: MASER
Short answer
MASER stands for Microwave Amplification by Stimulated Emission of Radiation. It achieves amplification through population inversion in a material (e.g., ruby) pumped to a higher energy level. Extremely low noise temperature (few kelvin) is obtained by cryogenic cooling, making it ideal for radio telescopes and deep-space receivers.
Write a short note on MASER.
MASER stands for Microwave Amplification by Stimulated Emission of Radiation. It is a very low-noise microwave amplifier or oscillator that uses stimulated emission from atoms or molecules. C. H. Townes built the first one in 1954, an ammonia maser at 23.87 GHz.
Principle
- An atom in an upper energy level E₂ can be pushed down to E₁ by an incoming photon of frequency f = (E₂ − E₁)/h. It then emits a second photon of the same frequency and phase. This is stimulated emission.
- Amplification needs population inversion, meaning more atoms in E₂ than in E₁. This is obtained by pumping.
- In the common three-level solid-state maser (ruby, Cr³⁺ in Al₂O₃), a pump signal at f₁₃ lifts atoms from level 1 to level 3. Level 3 then becomes more populated than level 2, so a signal at f₃₂ is amplified. The levels are tuned by a DC magnetic field (Zeeman splitting).
E3 ------------ <- pump f13 raises atoms
| signal f32 amplified
E2 ------------
E1 ------------
Features
- Extremely low noise temperature (a few kelvin), because the active medium is cooled to liquid-helium temperature.
- Narrow bandwidth and low output power. Needs cryogenic cooling and a magnetic field.
Applications: front-end amplifiers in radio telescopes and deep-space communication receivers, and atomic frequency standards (the hydrogen maser at 1.42 GHz).
✓ Answer checked by Claude Opus 5.5 (high effort)