Collimate Light from an LED | Thorlabs Insights

Collimating light from an LED or other large, incoherent source can be a surprisingly challenging task. The emitter’s size and the collimating lens’ focal length and numerical aperture (NA) all influence the characteristics of the collimated beam. It can also be hard to know when the lens is positioned optimally. In this video, two lenses with different NAs and focal lengths are used to demonstrate a couple of collimation approaches. In addition, the emerging image of the emitter and other typical features of beams provided by collimating lenses are explored.

Two significant collimated beam properties are divergence and optical power. As shown in this demonstration, when two lenses have the same diameter, more light is collected when the focal length is smaller, since the NA is larger, but at the cost of increased collimated beam divergence. The divergence is also affected by the light emitter’s physical size. Assuming the same lens is used, the collimated beam’s divergence is larger when the emitter is larger.

One consequence of a larger divergence is that the beam’s irradiance (optical power per area) decreases at a faster rate with increasing distance from the lens. Another consequence is that the collimated region is shorter. The collimated region can be described as the part of the beam where rays from across the entire emitter overlap, which is usually close to the lens. With increasing distance from the lens, divergence separates the rays into different bundles, according to their point of origin, revealing an image of the emitter. Seeing an image can be unexpected, since it is not predicted by the thin lens equation and can create unexpected artifacts in an application.

00:00 - Introduction
00:41 – Divergence & Collimation Overview.
03:28 – Collimation with 0.76 NA Lens
05:50 – Collimated Beam Features
06:46 – Collimate with 0.24 NA Lens
08:34 – Collimated Beam Features

Components used in this Demonstration Include:
- LEDD1B T-Cube LED Driver: https://www.thorlabs.com/newgrouppage...
- M505L4 Mounted LED, 505 nm: https://www.thorlabs.com/newgrouppage...
- SM2A6 Adapter (SM2 to SM1 threads) to Mount LED: https://www.thorlabs.com/newgrouppage...
- SM1T2 Coupler, 0.5” Long, External SM1 Threads, to Mount LED: https://www.thorlabs.com/newgrouppage...
-SM1M05 Lens Tube, 0.5” Long, Internal SM1 Threads: https://www.thorlabs.com/newgrouppage...
- LCP34 Cage Plate, 60 mm, SM2 Threads: https://www.thorlabs.com/newgrouppage...
--ER6 Cage Rod: https://www.thorlabs.com/newgrouppage...
- C60L24 Cage System Cover, 60 mm: https://www.thorlabs.com/newgrouppage...
- ACL50832U Aspheric Condenser Lens, Ø2”, NA 0.76, f = 32 mm: https://www.thorlabs.com/newgrouppage...
- AL50100M Mounted Aspheric Lens, Ø50 mm, NA 0.24, f = 100 mm: https://www.thorlabs.com/newgrouppage...
- LCP34T Cage Plate, 60 mm, SM2 Threads: https://www.thorlabs.com/newgrouppage...
- PM400 Power Meter: https://www.thorlabs.com/newgrouppage...
- S425C-L Thermal Power sensor: https://www.thorlabs.com/newgrouppage...
- LA1002 Plano-Convex Lens, Ø75 mm, f – 150 mm: https://www.thorlabs.com/newgrouppage...
-KS3 Kinematic Mirror Mount, Ø3”: https://www.thorlabs.com/newgrouppage...
-EDU-VS1 Viewing Screen: https://www.thorlabs.com/newgrouppage...
- MB412 Aluminum Breadboard: https://www.thorlabs.com/newgrouppage...
- BA2 Mounting Base: https://www.thorlabs.com/newgrouppage...
- Post Collars: https://www.thorlabs.com/newgrouppage...
- Optical Posts: https://www.thorlabs.com/newgrouppage...
- Optical Post Holders: https://www.thorlabs.com/newgrouppage...

For more photonics how-to videos, visit https://www.thorlabs.com/newgrouppage...