CLT Laser Physics & Types 2 — Questions and Answers
Question 1: Which laser type uses a mixture of helium and neon gases to produce a red beam at 632.8 nm?
- CO2 laser
- Nd:YAG laser
- He-Ne laser (Correct answer)
- Argon ion laser
Correct answer: He-Ne laser
The helium-neon (He-Ne) laser emits a characteristic red beam at 632.8 nm by exciting neon atoms via energy transfer from metastable helium atoms.
Question 2: What is the term for the process in which an excited atom releases a photon spontaneously without external stimulation?
- Stimulated emission
- Absorption
- Spontaneous emission (Correct answer)
- Population inversion
Correct answer: Spontaneous emission
Spontaneous emission occurs when an excited atom returns to a lower energy state and releases a photon without any triggering event.
Question 3: In a semiconductor diode laser, what confines the light within the active region?
- External mirrors
- The p-n junction's refractive index difference (Correct answer)
- A Brewster window
- An external etalon
Correct answer: The p-n junction's refractive index difference
The difference in refractive index between the active p-n junction layer and the surrounding cladding layers creates a waveguide that confines light.
Question 4: Which laser medium produces emission in the mid-infrared range and is widely used for cutting and welding metals?
- Ruby laser
- He-Ne laser
- CO2 laser (Correct answer)
- Excimer laser
Correct answer: CO2 laser
The CO2 laser emits at 10.6 µm in the mid-infrared and is highly absorbed by metals, making it ideal for industrial cutting and welding.
Question 5: What property distinguishes laser light from ordinary white light in terms of phase relationship?
- Higher intensity
- Coherence (Correct answer)
- Broader spectrum
- Random polarization
Correct answer: Coherence
Laser light is coherent, meaning all photons share the same phase, frequency, and direction, unlike the random phases of ordinary light.
Question 6: The gain bandwidth of a laser medium determines which of the following?
- The maximum output power
- The range of wavelengths over which lasing can occur (Correct answer)
- The pump threshold current
- The beam divergence angle
Correct answer: The range of wavelengths over which lasing can occur
Gain bandwidth is the spectral range over which the medium provides net amplification, setting the possible lasing wavelengths.
Question 7: Which of the following best describes a four-level laser system compared to a three-level system?
- It requires higher pump power to reach threshold
- Its lower laser level is rapidly depopulated, lowering threshold (Correct answer)
- It always operates in pulsed mode only
- It uses two separate gain media
Correct answer: Its lower laser level is rapidly depopulated, lowering threshold
In a four-level system the lower laser level is quickly emptied by fast relaxation, so population inversion is easier to achieve and threshold pump power is lower.
CLT Laser Physics & Types 2
Which laser type uses a mixture of helium and neon gases to produce a red beam at 632.8 nm?