Collimate Light from an LED | Thorlabs Insights

Tutorial: Collimating Light from an LED

Overview:

In this tutorial, we will demonstrate the approach used to collimate a highly divergent light source with a relatively large emitter size using a 505 nm mounted LED, two aspheric lenses, a viewing screen, and a thermal power meter and sensor. The goal is to balance between collecting more power from the LED and limiting the divergence of the collimated beam.

Materials Needed:

1. 505 nm mounted LED
2. Two aspheric lenses (Ø2" aspheric condenser lens with 0.76 NA and 32 mm focal length, 0.24 NA 100 mm focal length aspheric lens)
3. Viewing screen
4. Thermal power meter and sensor

Steps to Collimate Light from an LED:

1. Understand LED Properties:

   • Consider the angle and numerical aperture (NA) of the LED when collimating light.
   • Angle measures the full-width-half-max of the intensity profile with respect to the full angular range.
   • NA of the lens describes the largest cone of light the lens can collect.

2. Selecting the First Lens:

   • Use a Ø2" aspheric condenser lens with 0.76 NA and 32 mm focal length.
   • Position the lens close to the LED to capture more light but expect higher divergence.
   • Adjust the lens position until an image of the LED emitter is seen on the viewing screen.

3. Adjusting Lens Position:

   • Use an adjustable lens tube to iteratively push the image of the LED farther away.
   • Aim to produce a collimated beam, resembling an image at an infinitely long distance.

4. Check Divergence:

   • Expect a divergence of about 2.5° with the first lens.
   • Measure the beam diameter expansion at a distance of 24" from the output.

5. Assess Collimation:

   • Verify that the beam is collimated with no emitter structure close to the lens.
   • Record the size and power of the beam for further calculations.

6. Introduce the Second Lens:

   • Place the 0.24 NA 100 mm focal length aspheric lens in the cage system.
   • Expect a divergence of about 0.8° with this lens.

7. Check Beam Consistency:

   • Move the viewing screen back and forth to observe the consistency of the collimated beam diameter over the workspace.

8. Finalize Collimation:

   • Understand the compromise between beam power and divergence based on the numerical aperture, focal length, and emitter size.
   • Calculate the irradiance based on the recorded data.

9. Conclusion:

   • Understand that the total power in the output beam depends on the numerical aperture, while the divergence depends on the focal length and emitter size.
   • Contact Tech Support for any further questions.

By following these steps, you can effectively collimate light from an LED using the appropriate lenses and techniques to achieve the desired balance between power collection and beam divergence.