# BROADBAND FOCUSING FOR EXTREME MULTIMODAL MICROSCOPY

> **NIH NIH R21** · UNIVERSITY OF CALIFORNIA-IRVINE · 2024 · $145,448

## Abstract

Project Summary
Virtually all optical microscopes for biological imaging are based on refractive objective lenses.
The performance of these lenses approaches the theoretical limit, however, their use is limited
to the visible to near-infrared spectral range. Even within this range, their performance is only
guaranteed over a relatively narrow range, and broadband use is invariably affected by
chromatic aberrations. Another problem is the group delay dispersion that these lenses
introduce to short optical pulses, which reduces the efficiency of nonlinear optical (NLO) signal
generation in the microscope. Taken together, these shortcomings seriously compromise the
imaging properties of several NLO imaging modalities such as three-photon excited
fluorescence and third-harmonic generation. In addition, refractive objectives simply cannot be
used for NLO techniques that incorporate excitation light in the mid-infrared (MIR) range, such
as photothermal imaging and sum-frequency generation, promising technologies based on MIR
molecular contrast. The only viable alternative is the all-reflective Schwarzschild-Cassegrain
(SC) objective, which is inherently achromatic but suffers from a non-ideal pointspread function
and a center obscuration that limits throughput. Because of these limitations, SC lenses have
not found widespread use in biological imaging applications. This lack of performance is also
the reason why advances in exciting new MIR-based NLO imaging technologies have been
stifled: there simply are no high-performance high numerical focusing options available to
support these emerging imaging technologies.
 In this project, we develop a novel all-reflective high numerical aperture lens that
overcomes all limitations of the SC focusing lens. Based on a non-concentric design, this new
design features perfect color correction from the ultra-violet to the mid-infrared, exhibits a wide
field of view, dramatically reduces group delay dispersion and significantly improves throughput
by eliminating the center obscuration all together. This lens not only advances existing NLO
modalities that rely on broadband radiation, but also enables new technologies such as
photothermal imaging and SFG microscopy that have thus far suffered from low performance
focusing optics.

## Key facts

- **NIH application ID:** 10869930
- **Project number:** 5R21EB034084-02
- **Recipient organization:** UNIVERSITY OF CALIFORNIA-IRVINE
- **Principal Investigator:** Eric Olaf Potma
- **Activity code:** R21 (R01, R21, SBIR, etc.)
- **Funding institute:** NIH
- **Fiscal year:** 2024
- **Award amount:** $145,448
- **Award type:** 5
- **Project period:** 2023-07-01 → 2026-06-30

## Primary source

NIH RePORTER: https://reporter.nih.gov/project-details/10869930

## Citation

> US National Institutes of Health, RePORTER application 10869930, BROADBAND FOCUSING FOR EXTREME MULTIMODAL MICROSCOPY (5R21EB034084-02). Retrieved via AI Analytics 2026-05-25 from https://api.ai-analytics.org/grant/nih/10869930. Licensed CC0.

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