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

[@sambathbunkh]

Great video shows

[@Tferdz]

Maybe some optical tweezers setup later? How to align with scattering collection?

[@thorlabs]

@Tferdz Thanks for your suggestion! The setup and alignment of an optical tweezer system is a great topic. Do you use back-focal-plane interferometry when aligning with the scattered light? Are there certain aspects of your approach that you think are the most interesting?

[@Tferdz]

@@thorlabs we use this setup 10.1007/978-1-4939-6421-5_7. We add some complexities by sending rotating linear polarized light so we can collect torque measurements. Besides that it's forward scattering with collection by a PSD for the XY and a photo detector for Z. The reason we separate is that we put an iris to block light for the z detector since it makes it more z-sensitive by removing xy cross talk. But it would be cool to have a video where we can show people at least some basic of optical tweezers, which is not that complicated.

[@thorlabs]

@Tferdz This is really helpful, thanks! It is great to have a better understanding of the type of video that you would find useful to share, and we enjoyed learning more about your alignment approach!

[@user-cf5sm9cn6v]

Is a bi-convex lens suitable for collimating LED light?

[@thorlabs]

@user-cf5sm9cn6v The bi-convex lens shape can collimate light from an LED but the collimated beam will include more aberrations (particularly spherical) compared to other lens shapes. Whether this collimated beam is suitable depends on your particular application. Typically bi-convex lenses are used for imaging applications where both surfaces are used to focus the light to a point in the image plane.

[@EXYZ3]

thank you so much❤.this is litterally what i was searching for for monthes (and even better). this is perfection. also, can we focus a wide spectrum (eg: white leds) to form a nice beam?

[@thorlabs]

@EXYZ3 We are glad to have been able to help! Yes, this technique and these lenses are routinely used to collimate white-light LEDS. The resulting beam quality will be similar to the beam quality obtained when collimating light from narrower-spectrum LEDs. However, the collimated light from a white-light LED often includes a rainbow effect around the edges of the beam due to the lens’ chromatic aberrations. The color separation around the collimated beam’s edge can be reduced by using an achromatic lens in place of the aspheric condenser lens, although achromatic lenses typically have lower NAs than aspheric condensers.

[@DaLi-i1f]

您好，优秀的演示表明了不同NA和焦距的透镜对LED的准直作用。我有一个疑问，当透镜先调节出一个无限远成像的距离后，为什么还要继续调节透镜，使之不成像呢，这个是什么意思呢，形成平行光吗？

[@thorlabs]

Yes, the typical goal of collimating light is to provide an output beam with all the rays traveling parallel to one another. In an ideally collimated beam, the image of the light source would only be visible infinitely far away from the lens. In between the lens and infinity no image would be visible, because in the ideally collimated beam, rays from all points on the light source would overlap one another. However, in real world applications, it is typically not possible to move the image infinitely far away. This is because divergence separates the collimated ray bundles originating from different points on the light source. Due to this, one approach to collimating light from a relatively large source is to adjust the lens until the image is as far away as possible. When the viewable distance is too short to confirm that the image has been moved to the maximum possible distance, adjusting the lens to move the image past the farthest viewable distance is one way to push the expected image closer to its maximum possible distance.

[@ahmedmostafa-tf2vo]

Can this setub used to collimate light from a small filament lamp ?

[@thorlabs]

@ahmedmostafa-tf2vo Yes, lenses like the aspheric condensers used in this demonstration are regularly used to collimate light from a variety of different light sources, including filament lamps. Achromatic lenses are another option, since they can provide better results for broad-spectrum sources, but it can be difficult to find high-NA achromatic lenses. However, in all cases, the divergence of the collimated beam will increase as the size of the emitter increases.

[@ParTaban]

Hi your video is great but there are some contradictions: it is concluded from this video that a lense with higher NA and therefore with higher divergence, should provide lower irradiance as the beam area increses and the power decresea. but when you strat to explain experimentally, the results is vise versa. for lense with NA = 0.76 and f = 32 mm, irradiance is 177w/mm2, p = 0.29w and A= 1640mm2 for lense with NA=0.24 and f = 100mm, irradiance is 17w/mm2, p = 0.03w and A= 1735mm2 can you clarify this? do we expect a decresead iradiance with an incresead divergence which should be obtained wiht lense with NA = 0.76?

[@thorlabs]

@ParTaban The collimated beam with the higher 0.76 NA lens collected more power and provided a larger irradiance at the measurement plane in the video compared to the collimated beam provided by the lower 0.24 NA lens, as you pointed out in the measurements. However, the collimated beam output from the higher NA lens also has a larger divergence, so the irradiance will reduce at a quicker rate as the measurement plane moves away from the collimating lens. This means that while the lower NA lens has a lower overall irradiance near the collimating lens, the lower divergence provides a more consistent irradiance as the collimated beam travels away from the lens.

[@user-gz3sf7gy6z]

Your explanation is excellent, but I could not understand well

[@thorlabs]

@user-gz3sf7gy6z We are sorry that you had trouble understanding. Are there one or more topics that you would like us to explain in more detail in an upcoming video?

[@user-gz3sf7gy6z]

@@thorlabs I thank your efforts but I understood the subject.

[@JulianJXhori]

I think I know that Paul guy!

[@thorlabs]

@JulianJXhori Thanks Julian! Good luck in your upcoming physics courses!