Gallium-Arsenide Laser Diode

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What primary function do the polished front and rear faces of a Gallium-Arsenide laser diode serve?

To act as a resonant cavity for stimulated emission. (correct)
To provide mechanical support to the crystal structure.
To facilitate external electrical connections.
To prevent lasing action in unwanted directions.

In a heavily doped p-n junction of a GaAs laser diode, what is the position of the Fermi level on the n-side relative to the conduction band at thermal equilibrium?

The Fermi level lies within the valence band.
The Fermi level is located at the middle of the band gap.
The Fermi level aligns with the top of the valence band.
The Fermi level is pushed into the conduction band. (correct)

What is the primary role of applying a forward bias to the p-n junction in a GaAs semiconductor laser?

To overcome the potential barrier and inject charge carriers. (correct)
To decrease the rate of spontaneous emission.
To increase the resistance of the junction.
To widen the depletion region.

What happens in the active region of a GaAs laser diode when the current exceeds the threshold value?

Population inversion is achieved, leading to stimulated emission. (C) Signup and view all the answers

What determines the wavelength of light emitted by a GaAs semiconductor laser?

The energy gap of the GaAs material. (D) Signup and view all the answers

Why are the other two faces (besides the polished ones) of a Gallium-Arsenide laser diode roughened?

To prevent laser action in those directions. (B) Signup and view all the answers

Before a suitable forward bias is applied to a p-n junction in a GaAs laser, what type of emission is predominant when electrons and holes recombine?

Spontaneous emission. (A) Signup and view all the answers

What is the approximate wavelength of light emitted by a Gallium-Arsenide (GaAs) laser?

$8400 \text{ Å}$ (A) Signup and view all the answers

Which characteristic of laser beams allows them to be used in laser range finders for precise distance measurements in defense applications?

Their monochromaticity and unidirectionality, enabling focused and directional transmission and reception. (B) Signup and view all the answers

In LASIK eye surgery, what role does the laser play in correcting a patient's vision?

The laser reshapes the cornea to focus light correctly on the retina. (D) Signup and view all the answers

What is the primary advantage of using CO2 lasers in superficial cancer treatments, such as skin cancer?

Their precision and shallow cutting depth, minimizing damage to surrounding tissue. (B) Signup and view all the answers

What is the function of the photoconductor drum in a laser printer?

It forms a pattern of electrostatically charged dots to attract toner. (C) Signup and view all the answers

Why are lasers used in skin treatments like wrinkle reduction and scar removal?

Lasers can precisely remove layers of damaged skin and stimulate collagen production. (D) Signup and view all the answers

In laser range finders, what is the purpose of the optical filter before the signal reaches the photomultiplier in the receiver?

To filter out unwanted noise signals, ensuring a purer signal is amplified. (D) Signup and view all the answers

What is the role of a semiconductor diode laser in a laser printer?

To produce a concentrated beam of light that forms an electrostatic pattern on the photoconductor drum. (D) Signup and view all the answers

How does laser toning and tightening improve skin appearance?

By using lasers to penetrate deeper skin layers, addressing sun damage and promoting collagen production. (B) Signup and view all the answers

What is the primary role of a metastable state in achieving laser action?

To allow for a longer lifetime of atoms in an excited state, enabling population inversion. (B) Signup and view all the answers

Why is population inversion a necessary condition for laser action?

It increases the probability of stimulated emission over absorption, leading to light amplification. (B) Signup and view all the answers

In a laser system, what is the purpose of the pumping process?

To supply energy to the active medium to achieve population inversion. (B) Signup and view all the answers

What is the key difference between optical pumping and electrical pumping in laser systems?

Optical pumping uses light to excite atoms, while electrical pumping uses electrical energy. (A) Signup and view all the answers

What role do 'active centers' play within the active medium of a laser?

They are responsible for stimulated emission and light amplification. (C) Signup and view all the answers

What is the primary function of the laser cavity in a laser system?

To provide feedback of photons to stimulate further emission and amplify the light. (D) Signup and view all the answers

In the context of laser operation, what is the relationship between energy levels E1, E2, and E3, where E3 > E2 > E1, and E2 is the metastable state?

Atoms are excited from E1 to E3, then undergo spontaneous transition to the metastable state E2, allowing population inversion between E2 and E1. (B) Signup and view all the answers

Consider a laser system where the active medium initially has a greater population in the lower energy level (E1) than in the higher energy level (E2). Which of the following actions is essential to initiate laser action?

Supply energy to the active medium via pumping to achieve population inversion between E2 and E1. (C) Signup and view all the answers

Semiconductor Laser

A laser where the active medium is made of semiconducting materials.

GaAs Laser Construction

A single GaAs crystal, heavily doped with n-type and p-type materials, forming a small diode.