Lecture 10 focusing and colimating
- 1. FOCUSING AND COLLIMATING Prof. Sekartedjo Iwan Cony Setiadi
- 2. • An introduction to the use of lenses to solve optical applications can begin with the elements of ray tracing. • By ideal thin lens, we mean a lens whose thickness is sufficiently small that it does not contribute to its focal length. • We can also use basic geometry to look at the magnification of a lens This is the Gaussian lens equation. This equation provides the fundamental relation between the focal length of the lens and the size of the optical system 1 𝑓 = 1 𝑠% + 1 𝑠' REVIEW
- 3. Application 1: Focusing a Collimated Laser Beam Application 2: Collimating Light from a Point Source Simple Application
- 4. Application 3: Expanding a Laser Beam Simple Application Application 4: Focusing an Extended Source to a Small Spot
- 6. Beam Collimator Near-Zero Divergence Although lasers diverge slowly, the beam diameter enlarges sufficiently over a few meters. Collimator, device for changing the diverging light or radiation from a point source into a parallel beam.
- 7. • A collimated beam of light is a beam (typically a laser beam) which has a low beam divergence, so that the beam radius does not undergo significant changes within moderate propagation distances. • A divergent beam can be collimated with a beam collimator device, which in simple case is essentially a lens or a curved mirror BEAM EXPANDER What is divergence? Divergence describes the expansion of a laser beam over a long distance
- 8. Beam Expander The beam expanders increase the diameter of a collimated input beam to a larger collimated output beam. Beam expanders are used in applications such as laser scanning, interferometry, and remote sensing. Two type of laser beam expander: Keplerian and Galilean Keplerian beam expandersGalilean beam expanders
- 9. • When using the Keplerian or Galilean designs in laser beam expander applications, it is important to be able to calculate the output beam divergence. • This determines the deviation from a perfectly collimated source. The beam divergence is dependent on the diameters of the input and output laser beam • In addition, it is important to be able to calculate the output beam diameter at a specific working distance (L). The output beam diameter is a function of the input beam diameter and the beam divergence after a specific working distance (L)
- 10. A laser's input beam diameter and divergence can be used to calculate the output beam diameter at a specific working distance.
- 11. Application 1. Reducing Power Density 2. Minimizing Beam Diameter at a Distance 3. Minimizing Focused Spot Size 4. Laser Beam Size Compensation
- 12. Beam Shaper • In general, a beam shaper (or beam converter) is an optical device which somehow reshapes a light beam, i.e., it modifies its spatial profile. • In various industries there is a need to focus a laser beam to a well-defined size and shape with uniform intensity (flat top). • A flat top spot enables uniform laser treatment of the working surface, and maintains the same active area regardless of pulse energy.
- 13. Diffractive Optical Element ¨ A diffractive optical element (DOE) uses thin micro-structure patterns to alter the phase of the light that is propagated through it. ¨ Those micro-structures, once properly designed, can manipulate the light to almost any desired intensity profile or shape. ¨ Through in-phase manipulation of the input beam, We can achieve virtually limitless and, most importantly, speckle-free intensity profiles in the output beam.
- 14. The beam shaping element is a diffractive optical element (DOE) used to transform a near-gaussian incident laser beam into a uniform- intensity spot of either round, rectangular, square, line or other shape with sharp edges in a specific work plane. Each beam shaper is designed for use with a specific set of optical system parameters: • Wavelength • Input Beam Size (D) • Output Spot Size (d)
- 16. Why do we need beam shaper?
- 19. Discussion Question: Do you need to get intense light delivered at a distance? There are two choices: 1) Collimate the light or 2) Focus the light. ¨ Collimation expands the beam and sends it forward in relatively parallel beams. ¨ A focuser mounts on a collimator and either shrinks or magnifies the spot at a specific working distance. Which option is best for you?