Converging thermal lenses, and optical systems, kits, and methods for formation and use thereof
A converging thermal lens is transiently formed by directing a shaped pulsed light beam having at least a first wavelength to a thermo-optic material, whereby the thermo-optic material absorbs the light beam and experiences local heating in response thereto. The heating induces a refractive index profile in the thermo-optic material that temporarily forms the converging thermal lens. In some embodiments, the refractive index of the thermo-optic material has a negative temperature dependence, and the pulsed light beam is shaped to have an inverted light pattern with a maximum intensity in an outer region of the beam cross-section. Alternatively, in some embodiments, the refractive index of the thermo-optic material has a positive temperature dependence, and the pulsed light beam is shaped to have a radially-varying light pattern with a maximum intensity in a central region of the beam cross-section.
1. An optical system comprising:
a first light source providing a focus-activation beam of light having at least a first wavelength;
a beam-shaping optical assembly comprising one or more optical components disposed in or along an optical path to a sample, the beam-shaping optical assembly forming the focus-activation beam from the first light source to have a radially-varying light pattern;
a thermo-optic material disposed in the optical path before a target portion of a sample, the thermo-optic material absorbing light at the first wavelength, a temperature of the thermo-optic material increasing in response to said absorption; and
a transient, converging thermal lens formed in the thermo-optic material by a heating-induced refractive index profile generated by the absorption of the focus-activation beam with the radially-varying light pattern,
wherein:
a temperature dependence of refractive index of the thermo-optic material is negative, and the radially-varying light pattern is an inverted light pattern having a minimum or zero intensity within a central region and a maximum intensity within an outer region surrounding the central region; or
a temperature dependence of refractive index of the thermo-optic material is positive, and the radially-varying light pattern has a maximum intensity within a central region and a minimum or zero intensity within an outer region surrounding the central region.
2. The optical system of claim 1 , wherein the beam-shaping optical assembly comprises one or more diffractive optical elements, one or more refractive optical elements, or any combination thereof.
3. The optical system of claim 1 , wherein the beam-shaping optical assembly comprises a vortex phase plate, a spatial light modulator (SLM), a digital micromirror device (DMD), or any combination thereof.
4. The optical system of claim 3 , wherein the first light source provides the focus-activation beam as substantially monochromatic light having the first wavelength.
5. The optical system of claim 1 , further comprising:
a second light source providing a probe beam of light having a second wavelength different from the first wavelength,
wherein the thermo-optic material absorbs light at the first wavelength different than light at the second wavelength.
6. The optical system of claim 1 , wherein:
the thermo-optic material comprises a thermal lensing member disposed in the optical path before the sample,
the thermal lensing member comprises glass, polymer, ceramic, a container with liquid solution therein, or any combination thereof, and
the thermal lensing member has a material composition thereof tailored to absorb light at the first wavelength.
7. The optical system of claim 1 , further comprising:
an objective lens disposed in the optical path before the sample,
wherein the optical system is configured as an optical microscope.
8. The optical system of claim 1 , wherein the thermo-optic material comprises a second portion of the sample disposed before the target portion.
9. The optical system of claim 1 , wherein the first light source comprises a pulsed laser that outputs a train of optical pulses as the focus-activation beam, and the converging thermal lens is formed in the thermo-optic material by the heating-induced refractive index profile generated by absorption of a single one of the optical pulses of the train.
10. The optical system of claim 9 , wherein one or more of the optical pulses has a pulse length less than 500 ns so as to minimize heat diffusion during operation of the thermal lens.
11. A kit for improving resolution of an optical microscope, the optical microscope having an objective lens and a probe beam light source, the kit comprising:
a focus-activation light source constructed to provide a beam of light having at least a first wavelength that is different from a wavelength emitted by the probe beam light source;
a beam-shaping optical assembly comprising one or more optical components to be disposed in or along an optical path to a sample, the beam-shaping optical assembly being constructed to form the beam from the focus-activation light source to have a radially-varying light pattern; and
a thermal lensing member constructed to be disposed in the optical path before the sample, the thermal lensing member being constructed to absorb light at the first wavelength such that a temperature of the thermal lensing member increases in response to said absorption so as to form a transient, converging thermal lens, the thermal lensing member absorbing light at the first wavelength different than light at the wavelength emitted by the probe beam light source,
wherein:
a temperature dependence of refractive index of the thermal lensing member is negative, and the radially-varying light pattern is an inverted light pattern having a minimum or zero intensity within a central region and a maximum intensity within an outer region surrounding the central region; or
a temperature dependence of refractive index of the thermal lensing member is positive, and the radially-varying light pattern has a maximum intensity within a central region and a minimum or zero intensity within an outer region surrounding the central region.
12. The kit of claim 11 , wherein the thermal lensing member comprises glass, polymer, ceramic, a container with liquid solution therein, or any combination thereof, and the thermal lensing member has a material composition thereof tailored to absorb light at the first wavelength.
13. The kit of claim 11 , wherein the thermal lensing member is substantially transparent to light at the wavelength emitted by the probe beam light source.
14. The kit of claim 11 , wherein the beam-shaping optical assembly comprises one or more diffractive optical elements, one or more refractive optical elements, a vortex phase plate, a spatial light modulator (SLM), a digital micromirror device (DMD), or any combination thereof.
15. The kit of claim 11 , wherein:
the focus-activation light source comprises a laser that outputs a train of optical pulses as the beam, and
the focus-activation light source and the thermal lensing member are configured such that a converging thermal lens is formed in the thermal lensing member by a heating-induced refractive index profile generated by absorption of a single one of the optical pulses of the train.
16. The kit of claim 15 , wherein one or more of the optical pulses has a pulse length less than 500 ns so as to minimize heat diffusion during operation of the thermal lens.
17. A method comprising:
(a) forming a transient, converging thermal lens by:
generating a first beam of light having at least a first wavelength;
shaping the first beam to have a radially-varying light pattern; and
directing the shaped first beam to a thermo-optic material, the thermo-optic material absorbing light at the first wavelength, a temperature of the thermo-optic material increasing in response to said absorption,
wherein the thermal lens is formed in the thermo-optic material by a heating-induced refractive index profile generated by the absorption of the shaped first beam with the radially-varying light pattern, and
wherein:
a temperature dependence of refractive index of the thermo-optic material is negative, and the radially-varying light pattern is an inverted light pattern having a minimum or zero intensity within a central region and a maximum intensity within an outer region surrounding the central region; or
a temperature dependence of refractive index of the thermo-optic material is positive, and the radially-varying light pattern has a maximum intensity within a central region and a minimum or zero intensity within an outer region surrounding the central region.
18. The method of claim 17 , further comprising:
(b) within 10 μs after (a), imaging a sample using at least the converging thermal lens by:
generating a second beam of light having a second wavelength different from the first wavelength;
using at least the converging thermal lens, focusing the second beam onto a target portion of the sample; and
detecting light from the target portion of the sample,
wherein the thermo-optic material absorbs light at the first wavelength different than light at the second wavelength,
the first beam comprises a train of optical pulses, and
the converging thermal lens is formed in the thermo-optic material by the heating-induced refractive index profile generated by absorption of a single one of the optical pulses of the train.
19. The method of claim 17 , further comprising:
(b) within 1-10 ms after (a), imaging a sample using at least the converging thermal lens by:
generating a second beam of light having a second wavelength different from the first wavelength;
using at least the converging thermal lens, focusing the second beam onto a target portion of the sample; and
detecting light from the target portion of the sample,
wherein the thermo-optic material absorbs light at the first wavelength different than light at the second wavelength, and
the heating-induced refractive index profile of the converging thermal lens during (b) evolves from heat diffusion within the thermo-optic material.
20. The method of claim 17 , wherein the shaping of (a) comprises using one or more diffractive optical elements, one or more refractive optical elements, a vortex phase plate, a spatial light modulator (SLM), a digital micromirror device (DMD), or any combination thereof to shape the first beam to have a light pattern with intensity that varies radially.
21. The method of claim 17 , wherein:
the thermo-optic material comprises a thermal lensing member that is disposed in an optical path before a sample, the thermal lensing member having a material composition tailored to absorb light at the first wavelength, or
the thermo-optic material comprises a portion of a sample before a target portion of the sample.