CLT Laser Physics & Types 3 â Questions and Answers
Question 1: What is the primary gain medium in an erbium-doped fiber amplifier (EDFA), and at what wavelength does it operate?
- Nd ions at 1064 nm
- ErÂłâș ions at ~1550 nm (Correct answer)
- Yb ions at 976 nm
- Ho ions at 2090 nm
Correct answer: ErÂłâș ions at ~1550 nm
EDFAs use erbium ions (ErÂłâș) doped into silica fiber and amplify signals near 1550 nm, which coincides with the low-loss window of optical fiber.
Question 2: In a Q-switched laser, what happens when the Q-switch opens?
- The pump source is turned off
- Cavity loss suddenly drops, releasing stored energy as a short intense pulse (Correct answer)
- The gain medium is cooled rapidly
- The output coupler reflectivity increases to 100%
Correct answer: Cavity loss suddenly drops, releasing stored energy as a short intense pulse
Opening the Q-switch removes the artificially high intracavity loss, causing the large stored population inversion to deplete rapidly as a high-peak-power pulse.
Question 3: Which laser type uses an organic dye dissolved in a solvent as the gain medium?
- Alexandrite laser
- Dye laser (Correct answer)
- Fiber laser
- Diode-pumped solid-state laser
Correct answer: Dye laser
Dye lasers use fluorescent organic dyes in liquid solution as the gain medium and are tunable over a broad wavelength range.
Question 4: What does the term 'TEMââ mode' indicate about a laser beam?
- The beam has the highest possible divergence
- The beam has a Gaussian intensity profile with the smallest beam waist (Correct answer)
- The beam is multimode with random polarization
- The beam propagates only in pulsed operation
Correct answer: The beam has a Gaussian intensity profile with the smallest beam waist
TEMââ is the fundamental transverse electromagnetic mode, characterized by a Gaussian profile and the lowest beam divergence for a given aperture.
Question 5: Excimer lasers produce UV radiation by using which type of gain medium?
- Rare-earth doped crystals
- Unstable noble-gas halide molecules (Correct answer)
- Semiconductor junctions
- Metal vapor ions
Correct answer: Unstable noble-gas halide molecules
Excimer lasers use excited dimers or exciplexesâbound excited states of noble-gas halides like ArF or KrFâthat dissociate after emitting a UV photon.
Question 6: What is the significance of the 'threshold pump power' in a laser?
- The power at which the gain medium melts
- The minimum pump power at which gain exactly equals loss and lasing begins (Correct answer)
- The power level that maximizes beam quality
- The pump power required for CW operation only
Correct answer: The minimum pump power at which gain exactly equals loss and lasing begins
Threshold pump power is the minimum excitation level at which the round-trip gain equals round-trip loss, allowing sustained laser oscillation.
Question 7: A titanium-sapphire (Ti:Sapphire) laser is valued primarily for which characteristic?
- Its narrow, fixed emission line at 694 nm
- Its broad tunability from approximately 650 to 1100 nm (Correct answer)
- Its ability to operate at room temperature without cooling
- Its very low cost compared to diode lasers
Correct answer: Its broad tunability from approximately 650 to 1100 nm
Ti:Sapphire has an exceptionally broad gain bandwidth spanning roughly 650â1100 nm, making it widely tunable and capable of producing ultrashort pulses.
CLT Laser Physics & Types 3
What is the primary gain medium in an erbium-doped fiber amplifier (EDFA), and at what wavelength does it operate?