UNIQUE FEATURES OF THE POINT SOURCE MICROSCOPE (PSM)
The PSM is an unusually flexible optical test instrument with many unique features that set it apart from other optical test instruments. This is why we call it the “Swiss Army Knife” of optical instruments.
As opposed to most optical test instruments, the PSM is lightweight and has a small physical footprint. This means the PSM is used and mounted in places many other instruments cannot be used because of their size and mass. The PSM is easily mounted on a common xyz stage found in most optical labs and shops, and is easily built into other optical test instrumentation.
The PSM is multiple instruments in one like the Swiss Army Knife; used with a microscope objective it is an autostigmatic microscope useful for measuring radii of curvature and optical alignment among other uses, while used without an objective it is an autocollimator with a small aperture that is particularly useful for measuring errors in small prisms and windows.
The PSM is sensitive to a very wide range of intensities due to an adjustable internal laser diode light source and an adjustable camera. The internal source has a bright mode for aligning the PSM under ambient lighting of about 0.3mW and an adjustable range to avoid camera saturation of 25 μW down to 25 pW. The camera shutter is controllable over a range of 1000 and has a gain of 10. This gives a total dynamic range of intensities of easily handled of about 108.
While on the subject of intensity, the PSM is a Class I laser device so it may be used without laser safety restrictions as long as the PSM case remains closed. If additional power is needed the PSM may be coupled to an external light source via a single mode fiber. In addition, this feature gives the flexibility to use the PSM at any desired wavelength from 350 nm to over 2 μm. Clearly the PSM is not optimized over this wavelength range but it can still be used productively over this range (and with the appropriate camera for use beyond 1 μm).
In addition to being an autostigmatic microscope, the PSM is also a full field video microscope that is parfocal with the autostigmatic focus so you can see where the reflected spot focus is coming from. This is useful in case the reflected spot appears asymmetrical where it should not. The microscope may be focused on contamination or a defect in the surface being examined.
The sensitivity to focused spot motion is adjustable by changing objectives. While the PSM is supplied with a 10x objective, it will work with any infinity corrected objective from 100x to 2x. For even lower magnification and wider field of view, a simple plano-convex lens with an efl up to 150 mm may be used with the expected loss of lateral sensitivity.
Finally, just like a Swiss Army Knife, the PSM is completely portable. It has two USB cables to a laptop computer that is supplied with the PSM and is powered by the laptop which has the PSM Align software installed. The PSM is ready to use when received. Plug in the two USB cables, boot the computer, click on the PSM icon (be a little patient), and the video screen appears. You are now ready to work.
EASY SYSTEM ALIGNMENT
Optical alignment means positioning optically significant features like centers of curvatures and foci precisely where the optical design specifies.
The PSM enables this process by detecting and locating these optical features on the micrometer level and then relating them to mechanical fixtures, datums and features such as steel balls.
The PSM bridges the gap between optically significant features that cannot be mechanically probed and mechanical hardware such as bores, seats and mounts that can be located by conventional mechanical means.
CENTER AND ALIGN WITH ONE TOOL
The Point Source Microscope makes optical system alignment easy and deterministic, letting you perfectly align each component’s center-of-curvature and on-axis focused beam to the exact specifications. With both bright field imaging and autostigmatic microscopy, the PSM lets you align all optically important features quickly. Ergonomic features such as a bright laser diode setting make alignment simple, even in full room light.
The PSM lets you align the actual optical features, rather than relying on mechanical datums, so you can relax mechanical tolerances on your optics and mounts to reduce system costs. Use the PSM for everything from simple optics to complex systems such as Offner relays, atmospheric error correction systems and off-axis telescopes.
The PSM is invaluable for aligning aspheric optics, including off-axis aspheres. The PSM locates point images and shows the image shape as a star test. This unique system reduces alignment error to near zero by keeping the image in the correct location while adjusting the asphere to minimize aberrations.
ASPHERE ALIGNMENT
The PSM is also valuable for aligning aspheres and off-axis aspheres by using the aberrations aspheres produce when they are misaligned.
The PSM sees the reflected or transmitted Star image produced by the optical element or system in real time so there is optimum visual feedback as adjustments in alignment are made.
Since the PSM is sensitive to wavefront errors of as little as 8th wave rapid adjustment is made to near perfect alignment as witnessed by a symmetric image viewed going through focus.
RAPIDLY INSPECT LENS QUALITY
The PSM serves as an excellent incoming quality inspection tool, enabling fast verification of image shape, with λ/8 sensitivity, so you can easily resolve out-of specification optics without the expense or complication of using an interferometer. Further, the PSM can measure radius of curvature for production control, verify whether a lens meets specifications, or verify that a lens is correctly oriented. The PSM can even be mounted on a CMM for precise, non-contact x-y-z location.
OTHER OPTICAL METROLOGY USES
Picture of PSM aligning an off-axis parabola to a fiber feed using a plane mirror
In addition to its use for alignment, the PSM is useful for incoming inspection for radius of curvature, focal length, figure errors larger than 8th wave and centering errors.
Used as an autocollimator by removing the objective lens, the wedge in windows and parallelism of prism faces can be measured with 1 arc second precision.
The small beam size makes it particularly useful for small prisms.
NOTE ON USING PSM WITH OTHER LIGHT SOURCES
We are often asked if the PSM can be used at wavelengths other than the standard internal laser diode and LED sources at 635 nm. The answer is definitely yes by coupling in an external fiber feed light source.
The PSM performs to original specifications all the way from 405 to 1080 nm without any modification.
This makes the PSM useful for aligning laser diode sources to other components in an optical system, for example. The useful spectral range for the PSM may be even greater, we simply have not tried over an even broader range.
SPECIFICATIONS APPLICATIONS
SYSTEM TYPE
Portable, high-resolution video microscope
PROBE
Non-contact, 3D distance measuring probe for x-y-z stage or CMM
OBJECTIVES
10X Nikon standard; 4X or 20X optional
OBJECTIVE MOUNTS
Nikon M25 standard; rms, Mitutoyo, C-mount, Thorlabs SM1 and Right Angle Adapter optional
WORKING DISTANCE
> 17 mm with 10x objective
LATERAL SENSITIVITY
±0.5 mm range, 0.1μm sensitivity with 10X objective
AXIAL SENSITIVITY
±2 μm with 10x objective
ANGULAR SENSITIVITY
± 1.4° range, ±1 arc second sensitivity when used as an autocollimator (no objective)
VIDEO CAMERA
FLIR BlackflyS, 1440 x 1080 pixels 3.45 um pixels, 10 bit mono, >30 fps via USB3.1; other C/CS mount cameras color or mono optional
LIGHT SOURCES
Internal: full field 635 nm LED and laser diode point source, software controlled
Bright setting of laser diode for ambient lighting initial alignment
External: FC/APC connector for user supplied external fiber source Works from 405 to 1080 nm
OPTIONS
Optical Centering Station
Bench rail
Custom fixturing
COMPUTER
Dell laptop with USB3 interface, Windows 10 standard; desktop computer optional
INTERFACES
All USB3
SOFTWARE
PSMAlignTM software for real-time alignment and Control (LabVIEWTM license included)
WEIGHT
600 grams including10X objective and camera
DIMENSIONS
189 x 107 x 31 mm deep with objective and camera
