01 Source
Start with the laser you have.
Set a collimated flat-top or Gaussian beam, its diameter, and its wavelengths. This one is a 4 mm flat-top beam at 1.064 µm.
Laser beam path modeling
Know your spot size before you buy the optics.
Lay out your laser, mirrors, and lenses, and trace the beam through them. See where it focuses and how large the spot is, including the aberrations a spot-size formula leaves out.
Free to use · Runs in your browser · No lens-design training needed
- 01
Real lenses, not ideal ones
See how spherical aberration and chromatic focus shift move a stock lens’s focus away from its rated focal length.
- 02
The whole path at once
Source, fold mirrors, beam expander, and focusing lens, traced together with the spacing you’ll build.
- 03
Parts you can order
Insert any of 2,471 supported Thorlabs singlets. Each lens keeps its part number for your order.
Every beam, spot, and focus position on this page is traced by the lenskit engine as you scroll. Results are for each lens’s nominal prescription and don’t include manufacturing tolerances.
Analysis
Answer what a spot-size formula can’t. Before you order a part.
Every analysis runs on the system you built, in your browser. Start with the spot at your Image Plane, then look closer when a number surprises you.
01 Spot Diagram
How big is my spot?
Where the rays land on the Image Plane, with RMS and maximum spot radius and the centroid.
02 Through Focus
How much focus tolerance do I have?
Spot size at planes before and after the Image Plane, so you can see how quickly the focus grows as the working distance changes.
03 Chromatic Focus Shift
Does my alignment beam focus in the same place?
Paraxial focus position across the source spectrum, such as a 633 nm pointer next to a 1.064 µm process beam.
04 Spherical Aberration
Is the lens shape costing me?
How rays at the edge of the beam focus differently from rays at the center.
05 Point Spread Function (PSF)
What does the focused light look like?
The modeled intensity at the Image Plane, as a slice or a 3D surface.
06 Wavefront Error
How far is the lens from ideal?
The optical path difference across the beam, with RMS and peak-to-valley values.
Plots show the tour's LA1509 focusing lens with the Image Plane at 100 mm and a 1.064 µm source; Chromatic Focus Shift adds a 633 nm alignment beam. Some analyses are unavailable for extended sources.
Starter systems
Open a working system. Change it to match yours.
Open a starter close to what you’re building and inspect its layout and analyses, no account needed. Create an account to save your own copy and adapt the source, optics, and spacing.
01
Single focusing lens
A collimated beam and one lens. The quickest way to see where a real lens focuses and how fast the spot grows on either side.
02
Beam delivery with a 3× expander
The system from the tour: a 1.064 µm beam folded twice, expanded 3×, and focused by a stock Thorlabs lens. Swap a lens and see how the spot changes.
03
Scan lens at 10.6 µm
A multi-element scan lens for CO₂ lasers, traced at several field angles. See how the spot holds up across the scan field.
Keep the work moving
Send the design. Not a screenshot.
The layout, parts, and source settings stay together, so whoever opens your link sees the system you built and can run its analyses themselves.
Share a link that opens without an account.
Send an unlisted link to a colleague, customer, or supplier. They can inspect the system, run supported analyses, and save their own copy without changing yours.
Keep it private until you choose.
New systems and copies start private. Reopen them from your account, and recover unsaved drafts if a tab closes.
Bring in lenses you’ve already defined.
Import OSLO .len prescriptions, or save lenses to your personal library and reuse them in any system.
Before you get started
A few practical details.
What you need to begin, what the results include, and where lenskit stops.
Is lenskit free?
Yes, it’s free to use. Create an account, verify your email, and choose a username to start designing. Paid features may come later; their scope and pricing haven’t been decided.
Do I need to know Zemax?
No. You build the system from a source, lenses, mirrors, and an Image Plane in a visual layout, with nothing to install. You’ll still need your requirements, such as beam size, wavelength, and working distance, and the analyses use some optics vocabulary.
How much can I trust the results?
Lenskit traces rays through the exact prescriptions in your system, using each glass’s refractive index at your wavelengths. The results describe those nominal lenses. Manufacturing tolerances and coatings aren’t modeled, so treat a result as a design check, not a guarantee of built performance.
Can I start with stock optics?
Yes. Search supported Thorlabs singlets and insert them into your system; each lens keeps its part number. You can also enter your own prescription or reuse a lens from your personal library. Check current specifications with the supplier before ordering.
Are my designs public?
No. New designs are private. You can keep them private, share an unlisted link, or publish them in the gallery. Anyone with access can inspect the system and run supported analyses without an account. Editing someone else’s design saves an independent copy; the original doesn’t change.
Can I bring in designs from OSLO or Zemax?
You can import OSLO .len prescriptions with air-spaced singlets, conics and aspheres, catalog glasses, and single-axis tilted mirrors. Cemented lenses, lens tilts, and coordinate returns aren’t supported. You can also import and export lenskit JSON. Zemax import and export to other design programs aren’t currently available.
What can’t lenskit do?
It isn’t a full lens design suite. Whole-system optimization, tolerancing, stray light and non-sequential analysis, coating simulation, and Gaussian beam propagation aren’t available. Gaussian sources set the input beam profile, but the beam is traced with rays, not propagated as a Gaussian beam. Optimization refines one lens at a time.
Design your laser beam path before you build it.
Set up your source, add the optics you’re considering, and see the modeled focus before you order anything.
Free to use · Runs in your browser · No lens-design training needed