Confocal Optics for Selective Measurements

Confocal microscopy is an advanced imaging technique that enhances optical resolution and contrast compared to conventional brightfield microscopy. It achieves this by using specialized focusing optics to create a small, precisely focused probe at the specimen’s focal plane. Additionally, a pinhole aperture is positioned at the conjugate of the focal plane. This pinhole selectively blocks out-of-focus light, allowing only light originating from the plane of interest to be collected. By raster scanning a focused laser beam across the sample, 2D images are generated. Repeating this process at different planes enables a 3D reconstruction of the sample.

The thickness of the plane of interest is primarily determined by the focal depth of the system, which is explained in further detail below.

Gaussian Beams

A Gaussian beam is a type of electromagnetic beam that plays a crucial role in optics and laser physics. Its intensity profile and amplitude envelope in the transverse direction are described by a Gaussian function. This distribution means that the beam's intensity is highest at the center and gradually decreases towards the edges, creating a smooth, bell-shaped curve. Notably, the Gaussian beam represents the fundamental mode of many practical laser beams and is therefore used as an idealized model for their description.

Key parameters of this model include:

  • Beam Waist Diameter (ω0): The narrowest point of the Gaussian beam.
  • Beam Divergence half angle (θ): The opening angle of the Gaussian beam.
  • Rayleigh Length (ZR): The distance from the beam waist where the cross-section area of the beam doubles. It can be calculated using the formula:

ZR=π·ω02/λ,

      where λ represents the wavelength of the beam.

The plane of interest can then be given by the depth of focus d=2ZR.