Stanford EE259 I Gaussian beams, beam scanning techniques I 2023 I Lecture 16

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Introduction to Lidar

Lidar uses laser light to illuminate the environment and measure the time it takes for the light to return to the sensor.
Components of lidar include the laser source, optics, and photo detector.
Different types of laser sources used in lidar: edge-emitting lasers and vertical cavity surface emitting lasers.
Two techniques for illuminating the scene with laser light: flashlight lidar and scanning lidar.
Flashlight lidar emits a broad beam to illuminate the entire scene at once.
Scanning lidar uses a narrow beam and scans it across the scene.
Gaussian beams and the paraxial wave approximation are used to describe the propagation of laser beams.

The angle of divergence (Theta D) determines how quickly a beam diverges.
Theta D is almost equal to Lambda over Pi Omega zero, where Omega zero represents the waist radius of the beam at the focus point.
The angle of divergence is inversely proportional to the waist radius.
A smaller focus point results in quicker divergence.

Red laser coupled to a fiber, limiting the beam waist to the diameter of the fiber's core (10 microns).
Laser beam tightly focuses at the tip of the fiber but quickly diverges afterward.
Quick divergence leads to larger spot sizes when objects are farther away.

Optics, particularly lenses, are necessary for collimating beams that diverge quickly.
Lenses can transform the beam waist diameter to a much larger size, reducing divergence.
Lens collimates the beam coming out of the fiber, increasing beam diameter from 10 microns to approximately 7 millimeters.
Collimated beam does not diverge as quickly as the original beam, allowing for better visibility even at a distance.

Optics can be designed according to specific application requirements.
Lens selection based on desired beam diameter at a certain distance.
Optics, such as lenses, are essential for controlling the divergence angle of a beam.
Presenter acknowledges that the lens used in the demonstration was not designed for a red laser, but still serves to illustrate the purpose of optics in controlling divergence.