The LIG Nanowise SMAL (Super-Resolution Microsphere Amplifying Lens) is an optical device developed to capture lateral resolution beyond the diffraction limit offered by traditional microscopy. To evaluate its true resolving power, the SMAL lens was assessed using the Newport HIGHRES-1 USAF resolution target, which covers features as low as 137 nm, dimensions that conventional optical objectives cannot resolve.
This discussion illustrates how the SMAL lens can resolve the smallest features on the HIGHRES-1 target with considerable success, as well as comparing performance with both SEM ground-truth imaging and a traditional 100× high-NA objective.
The Newport HIGHRES-1 Target
The HIGHRES-1 incorporates a quartz substrate patterned with a 100 nm chromium layer to generate a high-precision USAF-1951 resolution chart. Its fine features – Group 11, Element 6, with 137 nm lines and 137 nm spaces (3,649 lp/mm) – are less than the diffraction limit that visible-light microscopy can achieve. Newport notes that to easily resolve these structures, SEM is the conventional approach, making the target an appropriate choice for evaluating super-resolution imaging performance.
Experimental Setup
SMAL Lens Optical Imaging Assembly
- LIG Nanowise SMAL™ lens mounted on LIG Nanowise microscope Nanoro M
- High-NA No immersion configuration
- Wideband LED illumination
- Scientific CMOS camera for image capture
The SMAL lens was arranged in an alignment that allowed maximization of near-field coupling. This facilitates imaging beyond the diffraction limit.
Control Imaging Using a 100× Objective Lens (UV-Enhanced Reference)
A high-quality 100× UV-capable objective (NA ≈ 1.2) was used as a control during the experiment alongside the application of a methodology reported by JMC Scientific Consulting for the Newport HIGHRES-2 slide.
The HIGHRES-2 also contains equivalent USAF feature dimensions to HIGHRES-1. At 313 nm UV illumination, the 100× objective achieved resolutions down to the ~150–200 nm range, incorporating Groups 10 and parts of Group 11. However, the finest of 137 nm structures (Group 11, Element 6) below or at the threshold of the limit of detection. This is in agreement with the theoretical diffraction limit, even when applying UV illumination.
This verifies performance as expected:
- 100× objective resolves down to ~150–200 nm
- Unable to resolve 137 nm
- Serves as a practical high-end optical reference, but cannot be considered a super-resolution method
Source: UV Microscopy – Resolution testing with the Newport Highres-2 USAF slide, JMC Scientific Consulting Ltd, April 16, 2022
SEM Imaging (Ground-Truth Reference)
Scanning electron microscopy was used to image the HIGHRES-1 target, which provided definitive ground-truth resolution. The SEM was able to resolve all features down to 137 nm line/space clearly. This validates the physical dimensions of the pattern. Therefore, SEM is the best-suited method for confirming true resolution because the 137 nm elements are beneath the diffraction limit of visible-light optics. The SEM image acts as the comparative performance benchmark for SMAL and 100× objective images.
Source: Newport website
Results
SEM Reference
- Fully resolves all groups and elements, including 137 nm features (Figure 1)
- Delivers precise verification of line width, spacing, and edge definition
- Establishes the physical limits of the target
Figure 1. SEM image of the Newport HIGHRES-1 sample target. Image Credit: LIG Nanowise
Standard 100× Objective
- Resolves features down to ~150–200 nm, depending on wavelength (Figure 2)
- Group 10 and partial Group 11 resolved under UV and white light
- 137 nm features appear blurred or merged and remain unresolved,
- Validates the classical diffraction limit for traditional optics
Figure 2. 100x immersion objective lens optical images of the Newport HIGHRES-1 target sample imaged in Visible Light (left) and UV (right). Image Credit: LIG Nanowise
SMAL Lens Performance
- Resolves the 137 nm features (Group 11, Element 6) with clarity
- Clear line/space separation with measurable contrast
- Resolution performance matches the SEM reference closely
- Exhibits true super-resolution capability beyond the 100× objective
Figure 3. DRY SMAL image of the Newport HIGHRES-1 target sample. Image Credit: LIG Nanowise
Comparative Summary
System Smallest Resolved Feature Group 11 Element 6 (137 nm) Notes
- SEM 137 nm - Resolved - Ground-truth benchmark
- 100× Objective - ~150–200 nm - Not resolved - Diffraction-limited
- SMAL Lens 137 nm - Resolved - Super-resolution
Conclusion
It was determined that by using the Newport HIGHRES-1 target, the LIG-Nanowise SMAL lens exhibits validated super-resolution imaging as it can resolve the smallest of 137 nm USAF features. This shows similar performance to SEM, making the instrument considerably superior to a standard 100× objective. This demonstrates that the SMAL lens is a compelling and practical tool for nanoscale imaging across the materials science discipline as well as for semiconductor inspection and nanofabrication quality control.
This information has been sourced, reviewed and adapted from materials provided by LIG Nanowise.
For more information on this source, please visit LIG Nanowise.