# US 11,994,472 B2 · Sub-wavelength Raman imaging with combined optical and electron excitation

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- Number: US 11,994,472 B2
- Document ID: US11994472B2
- Status: Granted
- Kind: B2
- Application number: 17/629,697
- Filed: 2020-07-24
- Published: 2022-08-25
- Granted: 2024-05-28
- Earliest claimed: 2019-07-26
- Assignees: The Board of Trustees of the Leland Stanford Junior University
- Applicants: The Board of Trustees of the Leland Stanford Junior University
- Inventors: Jennifer A. Dionne; Amr Ahmed Essawi Saleh; Daniel K. Angell
- Web page: https://patentgrep.com/patent/US11994472B2

## CPC

- G01N 21/65: Raman scattering
- H01J 37/226: {Optical arrangements for illuminating the object; optical arrangements for collecting light from the object}
- G01J 3/44: Raman spectrometry; Scattering spectrometry {; Fluorescence spectrometry}
- G01N 21/658: {enhancement Raman, e.g. surface plasmons}
- G01N 2021/655: {Stimulated Raman}
- H01J 2237/2003: Environmental cells
- G01N: INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES (measuring or testing apparatus or processes other than immunoassay, involving enzymes or microorganisms C12M, C12Q)
- H01J: ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS (spark-gaps H01T; electric arc lamps H05B31/00; particle accelerators H05H)
- G01J: MEASUREMENT OF INTENSITY, VELOCITY, SPECTRAL CONTENT, POLARISATION, PHASE OR PULSE CHARACTERISTICS OF INFRARED, VISIBLE OR ULTRAVIOLET LIGHT; COLORIMETRY; RADIATION PYROMETRY (light sources F21, H01J, H01K, H05B; investigating properties of materials by optical means G01N)

## Abstract

Improved stimulated Raman spectroscopy is provided by replacing the Stokes (or anti-Stokes) optical source with a localized electromagnetic emitter that is excited with a non-electromagnetic excitation. Such a localized emitter can be an efficient Stokes (or anti-Stokes) source for stimulated Raman spectroscopy, and can also provide deep sub-wavelength spatial resolution. In a preferred embodiment, an electron beam from an electron microscope is used to excite the localized emitter. This provides combined Raman imaging and electron microscopy that has the two imaging modalities inherently registered with each other.

## Claims

### Claim 1

A method of performing stimulated Raman spectroscopy on a sample, the method comprising:
providing optical pump radiation to the sample at a predetermined wavelength, wherein the sample defines a Raman-shifted wavelength relative to the predetermined wavelength;
disposing a localized electromagnetic emitter in proximity to the sample, wherein the localized electromagnetic emitter has an electromagnetic resonance at the Raman-shifted wavelength;
providing a non-electromagnetic excitation to the localized electromagnetic emitter configured to excite an electromagnetic mode of the localized electromagnetic emitter at the Raman-shifted wavelength; and
receiving a stimulated Raman signal from the sample.

### Claim 2 (depends on 1)

The method of claim 1, wherein the optical pump radiation has a full-width half-maximum linewidth of 1 nm or less.

### Claim 3 (depends on 1)

The method of claim 1, wherein the Raman-shifted wavelength is less than the predetermined wavelength.

### Claim 4 (depends on 1)

The method of claim 1, wherein the Raman-shifted wavelength is greater than the predetermined wavelength.

### Claim 5 (depends on 1)

The method of claim 1, wherein the non-electromagnetic excitation provided to the localized electromagnetic emitter is periodically modulated, and wherein lock-in detection is employed to improve a signal to noise ratio of the stimulated Raman signal.

### Claim 6 (depends on 1)

The method of claim 1, wherein the non-electromagnetic excitation is provided by an electron beam.

### Claim 7 (depends on 6)

The method of claim 6, wherein the electron beam is provided by an electron microscope, whereby simultaneous electron microscopy and Raman imaging is provided.

### Claim 8 (depends on 1)

The method of claim 1, wherein the localized electromagnetic emitter comprises a cathodoluminescent emitter.

### Claim 9 (depends on 1)

The method of claim 1, wherein the localized electromagnetic emitter comprises one or more nanoparticles.

### Claim 10 (depends on 9)

The method of claim 9, wherein a shape of the one or more nanoparticles is selected from the group consisting of: spheres and rods.

### Claim 11 (depends on 1)

The method of claim 1, wherein the electromagnetic resonance of the localized electromagnetic emitter is a plasmonic resonance.

### Claim 12 (depends on 11)

The method of claim 11, wherein the plasmonic resonance is a dark mode having reduced coupling to far-field radiation.

### Claim 13 (depends on 1)

The method of claim 1, wherein the localized electromagnetic emitter is chiral, whereby the stimulated Raman signal is responsive to chirality of the sample.