Laser Physics & Types Flashcards
7 cards from real CLT practice questions. Tap to flip, then mark Knew It or Still Learning — missed cards come back until you master them.
Read the first 7 Laser Physics & Types flashcards as text
What role do distributed Bragg reflectors (DBRs) play in semiconductor lasers?
Answer: They act as wavelength-selective mirrors replacing cleaved facets
DBRs are periodic stacks of alternating refractive-index layers that reflect a specific wavelength with very high reflectivity, serving as high-quality cavity mirrors.
Which physical mechanism causes 'thermal lensing' in a solid-state laser gain medium?
Answer: Temperature-induced refractive index gradient creating a focusing effect
Waste heat from pump absorption creates a radial temperature gradient in the crystal, and since refractive index depends on temperature, the medium acts like a lens.
What distinguishes a 'free-electron laser' (FEL) from all other laser types?
Answer: Its gain medium is a beam of relativistic electrons wiggled by a magnetic undulator
FELs produce stimulated emission from relativistic electrons oscillating through a periodic magnetic undulator, with no atomic or molecular gain medium involved.
In mode-locked lasers, what determines the pulse duration achievable?
Answer: The inverse of the gain bandwidth of the laser medium
Transform-limited pulse duration is inversely proportional to gain bandwidth; a broader bandwidth supports shorter pulses via the time-bandwidth product relationship.
What is the primary advantage of a diode-pumped solid-state (DPSS) laser over a flashlamp-pumped equivalent?
Answer: Higher wall-plug efficiency and longer pump source lifetime
Laser diodes convert electricity to light far more efficiently than flashlamps and last tens of thousands of hours, dramatically improving overall system efficiency and reliability.
Which laser operates by achieving population inversion between rotational-vibrational levels using a gas discharge, and emits in the far-infrared?
Answer: HCN laser
HCN (hydrogen cyanide) lasers emit in the far-infrared around 337 µm by exploiting rotational transitions in the vibrationally excited HCN molecule.
What is 'amplified spontaneous emission' (ASE) and why is it undesirable in a laser amplifier?
Answer: Spontaneous photons amplified by the gain medium along unintended paths, depleting inversion and adding noise
ASE occurs when spontaneously emitted photons travel through the gain medium and are amplified, consuming stored inversion and introducing broadband noise that degrades signal quality.