US 11,193,914 B2

Sheet 18 of 20

Dec. 7, 2021

U.S. Patent

BIVCY MEY nnn:

adopeauy

Ty wn

Sl ‘Old
x
90 FO B20 0
: + B0
- ST'0-
T0-
: ¢0°0-
<
Z0Z
108

0)

(a)



US 11,193,914 B2

Sheet 12 of 20

Dec. 7, 2021

U.S. Patent

9 10S Y10S

F106

él ‘DIA

e106

S106

VUNOWB 199}89S sursevasouy

T106


US 11,193,914 B2

3

disposed on a support substrate in panel A; converting the
liquid composition to a solid or gel superstratum in going
from panel A to panel B; and forming the photoacoustic
photon meter by lifting off a photoacoustic generative array
from the support substrate onto the superstratum and remov-
ing the superstratum with transferred array in going from
panel B to panel C;

FIG. 14 shows a process making a photoacoustic photon
meter that includes initial deposition of a liquid composition
ona photoacoustic generating pattern disposed on a support
substrate in panel A; converting the liquid composition to a
solid or gel superstratum, forming the photoacoustic photon
meter by lifting off'a photoacoustic generative array from the
support substrate onto the superstratum, and taking the
superstratum with transferred array and in going from panel
Ato B; flipping the superstratum with the array up side down
in going from panel B to C; adding another layer of
superstratum with different optical properties on top of the
flipped photoacoustic photon meter in going from panel C to
panel D:

FIG. 15 shows scattering of photons in a photon propa-
gating medium and subjecting an analyte volume disposed
in the propagation medium to photons in panel A; and in
panel B an enlarged view of the analyte volume on which a
photoacoustic photon meter is disposed;

FIG. 16 shows a process for performing photoacoustic
imaging with a photoacoustic photon meter;

FIG. 17 shows a configuration of a photoacoustic photon
meter for simultaneously determining photon fluence and
acoustic pressure;

FIG. 18 shows a photoacoustic generative array on a
support substrate before transferring to a superstratum in
panel A; in panel B a photoacoustic photon meter that
includes the photoacoustic generative array shown in panel

‘A with superstratum: and in panel C a graph of acoustic 3

pressure versus time obtained by a photoacoustic transducer
in the reflection position to measure the pressure from the
photoacoustic photon meter shown in panel B;

FIG. 19 shows a process of simultaneously measuring the
photoacoustic pressure and photon fluence by a photoacous-
tic photon meter including a carbon nanotube array where
the array has multiple connected carbon nanotube patches
with varied absorption coefficients in panel A; a graph of
photoacoustic signal versus time in panel B from different
portions of the photoacoustic photon meter measured by a
photoacoustic transducer shown in panel A; a graph of
photodetector signal versus time from different portions of
the photoacoustic photon meter shown in panel C; and a
graph of photoacoustic pressure and photodetector signals
from different portions of the photoacoustic photon meter
simultaneously measured by an ultrasound sensor and a
photodetector shown in panel D.

FIG. 20 shows a plurality of micrometer scale photoa-
coustic photon meters for resolution calibration in panel A;
and in panel B a graph of photoacoustic intensity along a line
across the plurality of the photoacoustic photon meters
shown in panel A for resolution analysis.

DETAILED DESCRIPTION

A detailed description of one or more embodiments is
presented herein by way of exemplification and not limita-
tion.

It has been discovered that photoacoustic photon meter
disclosed herein measures a spatial photon fluence, spectral
photon fluence, temperature, or pressure in a turbid medium.
Photon fluence refers to irradiating photon energy per unit

S

2

8

40

45

60

4

area or an irradiated number of photons per unit area. Spatial
photon fluence refers to a spatial distribution of the photon
fluence across a surface irradiated with photon. Spectral
photon fluence refers to photon fluence per unit bandwidth
of the wavelength of the irradiating light.

Advantageously, the photoacoustic photon meter over-
comes technical limitations of conventional devices that fail,
in a light-diffusing or light-absorbing material, to provide an
accurate local photon fluence measurement with varied
wavelength. Failure of such conventional devices can occur
because a spatial distribution of light-scattering or light-
absorbing entities disposed in a material may be non-
uniform, and an enemy or propagating direction or depth of
propagating photons in the material may not be spatially

5 homogeneous and can be wavelength-dependent.

In the photoacoustic photon meter, carbon nanotubes
(CNTs) can be arranged in a randomly distributed format or
a systematically aligned or ordered format, wherein the
CNTs absorb photons over a broad range of wavelengths and
convert optical energy to thermal or mechanical energy that
can be measured by a change in electrical conductivity of the
CNTs or via ultrasound pressure created from thermal con-
version by the CNTs of the absorption of the photons.

In an embodiment with reference to FIG. 1, FIG. 2, FIG.

5 3, and FIG. 4, photoacoustic photon meter 200 includes

photoacoustic generative array 203 that includes a plurality
of carbon nanotubes 204 disposed in photoacoustic gener-
ating pattern 205. Carbon nanotubes 204 receive photons
206 including optical energy 208 and produce thermal
energy 207 from optical energy 208. Superstratum 201
includes thermally expandable elastomer 202 on which
photoacoustic generative array 203 is fixedly disposed in
position on superstratum 201 to spatially conserve photoa-
coustic generating pattern 205. Superstratum 201 is optically
transparent to photons 206; receives thermal energy 207
from photoacoustic generative array 203; expands and con-
tracts in response to receipt of thermal energy 207; and
produces photoacoustic pressure waves 209 in response to
expansion and contraction 217. Photoacoustic pressure
waves 209 includes a photoacoustic intensity and photoa-
coustic frequency that are based upon an amount of optical
energy applied to carbon nanotubes 204 by photons 206, a
spatial photon fluence of photons 206, or a spectral photon
fluence of photons 206.

In an embodiment with reference to FIG. 4, photoacoustic
photon meter 200 includes photon propagation medium 210
disposed on superstratum 201 and in photoacoustic commu-
nication with superstratum 201. Photon propagation medium
210 receives photoacoustic pressure waves 209 from super-
stratum 201; and communicates photoacoustic pressure
waves 209 through photon propagation medium 210. Mea-
suring photoacoustic pressure waves 209 by photoacoustic
photon meter 200 can include configuring photoacoustic
transducer 211 in photoacoustic communication with photon
propagation medium 210 and superstratum 201. Photoa-
coustic transducer 211 receives the signal of photoacoustic
pressure waves 209 from photon propagation medium 210;
and produces electrical signal 212 from photoacoustic pres-
sure waves 209 and from which the optical fluence of
photons 206 can be determined.

According to an embodiment, with reference to FIG. 5,
photoacoustic photon meter 200 includes photoacoustic gen-
erative array 203 interposed between superstratum 201 and
secondary substrate 219.

With reference to FIG. 6, photoacoustic photon meter 200
can be configured as resolution target 220 or fluence target
221. Photoacoustic photon meter 200 configured as a reso-


US 11,193,914 B2

Sheet 3 of 20

Dec. 7, 2021

U.S. Patent

90%

§ ‘Dla

6

0:

:

90%

90%

906

906



US 11,193,914 B2

Sheet 19 of 20

Dec. 7, 2021

U.S. Patent

(sr) eu.

Ost SCT GOT Si OS SE OO

{g)*0
(yet
(oye
(s)*r
(pyr
(ey
{zy
(yen

ry

(gyn

(sy

(eet (1) ert

generat

°
00% -y
Oo
wo
oor &
DB
B
009 -F
Ss
oe
000T (9)
O'sz

SLE

GLE

(Aw) 2UBIS Yd Yeag-o}- 88d

&
3
et

iced)

6I ‘DIA

{sr} sw.
rae) TO oO To-
(9) q oe~
(aya
(9}'n ot~
igor
pe SFT
(e}Prt
(Prt i Ot
rye q
ics)

Go FIs OLS OOS 11S Les OSS 90S’ BIS

i

(¥)

{AW} (BUBIS vd


US 11,193,914 B2

9

plary light sources 218 include a nanosecond pulsed laser
diode, optical parametric oscillator nanosecond laser, dual
comb mode-lock frequency comb laser, and the like. It is
contemplated that light source 218 can be pulsed at a
repetition frequency from 1 Hz to 100 MHz, typically from
10 Hz to 100 kHz, with a pulse width from 1 fs to 1 ms,
specifically from 1 ns to 100 ns. Photons 206 can have a
wavelength from ultraviolet to mid-infrared, specifically
from 266 nm to 5000 nm. An energy of photons 206 can be
from 1 pJ to 100 mJ, specifically from 1 nJ to 1 J. An
optical fluence of photons 206 can be from 0.001 to 1 times
the ANSI limit (100 mJ/cm? at 520 nm), specifically from
0.1 mJ/em? to 100 mJ/cm?, wherein the ANSI limit varies as
a function of wavelength of light. In an embodiment, pho-
tons 206 have a wavelength of 520 nm, a fluence of 50.9
mJ/cm?, a repetition rate of 10 kHz, and a pulse width of 4
ns.

Carbon nanotubes 204 disposed on superstratum 201
receive photons 206, e.g.. from light source 218. Optical
energy 208 of photons 206 can be from 1 pl to 1 wl,
specifically from 1 nJ to 100 nJ. Carbon nanotubes 204 in
photoacoustic generative array 203 convert optical energy
208 to thermal energy 207 that is communicated to super-
stratum 201. Thermal energy 207 can be expressed by
1-exp(-thicknessxabsorption coefficient),

Superstratum 201 receives thermal energy 207 from pho-
toacoustic generative array 203 and converts thermal energy
207 to photoacoustic pressure waves 209 by repeated heat-
ing leading to expansion of thermally expandable elastomer

202 when photoacoustic generative array 203 receives pho- 3

tons 206 and rapidly accumulates optical energy before heat
dissipation during the irradiation of photons 206 by photoa-
coustic generative array 203 so that almost no thermal
energy 207 is communicated from photoacoustic generative

array 203 to superstratum 201 during the pulse duration time 3

by a pulsed laser. The rapidly accumulated thermal energy
induced mechanical expansion and contraction of the pho-
toacoustic generative array 203 to generate photoacoustic
pressure in the photoacoustic generative array 203 generates
local pressure transferred to superstratum 201. Photoacous-
tic pressure waves 209 have a photoacoustic intensity and
photoacoustic frequency. The photoacoustic intensity can be
from 1 kPa to 1 GPa. The photoacoustic frequency is in the
ultrasound frequency range and can be from 10 kHz to
several GHz.

Photon propagation medium 210 can receive photoacous-
tic pressure waves 209 from superstratum 201. Photon
propagation medium 210 can include gas, liquid, gel, or
solid to receive the acoustic pressure energy either directly
from the photoacoustic generative array 203 or from the
superstratum in contact with the photoacoustic generative
array 203 and convert the energy into propagating pressure
wave and can be water, single or multi-element gas, a
gel-like material such as hydrogel, or solid materials such as
metal and ceramic. Exemplary propagation media 210
includes water, NO, trace gas, and the like. It is contem-
plated that photon propagation medium 210 can have a
viscosity from 10 uPa-s (gas) to 1 mPars (water) for gas and
liquid, about 1 mPa‘s for water at room temperature. Photon
propagation medium 210 can have a frequency and tem-
perature dependent transmission efficiency with an absorp-
tion of 1 dB/km of a 10 kHz sound wave at room tempera-
ture in water. In an embodiment, photon propagation
medium 210 includes water.

Photoacoustic pressure waves 209 propagate through
photon propagation medium 210, and photoacoustic trans-
ducer 211 can receive photoacoustic pressure waves 209

40

45

10

from photon propagation medium 210. Photoacoustic trans-
ducer 211 can include ultrasound transducers, including a
surface material in contact with the photon propagation
medium 210 in one end and the other with an element to
convert sensed pressure signal to an electrical or optical
signal and can be a piezoelectric pressure sensor, Fabry-
Perot optical cavity sensor, metamaterial sensor, or other
hybrid sensor of such types. Exemplary photoacoustic trans-
ducers 211 include a hydrophone, optical cavity sensor,
microcantilever sensor, and the like.

Photoacoustic transducer 211 produces electrical signal
212 from receipt of photoacoustic pressure waves 209
Electrical signal 212 can include an intensity, pulse width,
time delay from the beginning time of the laser irradiation,
and frequency spectrum to measure the pressure wave
characteristics in the photon propagation medium 210,
reflecting the acoustic pressure characteristics generated
from the photoacoustic generative array 203 and can be a
time-traced voltage signal. Exemplary electrical signal 212
include peak-to-peak amplitude of the propagating pressure
wave packet, pulse width of the wave packet, and the delay
time from the beginning time of the laser irradiation, and the
like. The photoacoustic intensity can be from 1 kPa to 1
GPa. The photoacoustic frequency is in the ultrasound
frequency range and can be from 10 kHz to several GHz.
The amplitude is the peak-to-peak distance in volts mea-
sured from the propagating wave packet of the pressure
wave measured by a photoacoustic transducer. In an
embodiment, photoacoustic transducer 211 includes a focus-
ing piezoelectric transducer with a 50 MHz center detection
frequency and with a frontal end with about 6 mm in
diameter.

It is contemplated that the optical fluence of photons 206
is determined from electrical signal 212 measured by an
photoacoustic transducer 211 or from electrical signal mea-
sured by a photodetector 214. The optical fluence can
include a spatial photon fluence of photons 206 or a spectral
photon fluence of the photons 206. The spatial photon
fluence is a distribution of optical fluence as received over
photoacoustic generative array 203. The distribution can be
uniform or non-uniform across photoacoustic generative
array 203 so that an amount of optical energy irradiated onto
the carbon nanotubes 204 by the photons 206 across pho-
toacoustic generative array 203 can be the same for a
uniform distribution of spatial photon fluence or can be
different for a non-uniform distribution of spatial photon
fluence. In this respect, a spectral photon fluence can be
spatially uniform or non-uniform, e.g., having a Gaussian
distribution in space. A spectral photon fluence can also be
of some intensity distribution across the wavelength range,
based on a distribution of wavelengths of photons 206.

In an embodiment, e.g., as shown in FIG. 19, photode-

5 tector 214 is in optical communication with photoacoustic

generative array 203 and superstratum 201 and receives
photons 206 transmitted through photoacoustic generative
array 203 and superstratum 201. Photoacoustic transducer
211 produces electrical signal 212 from receipt of photoa-
coustic pressure waves 209. Electrical signal 212 can
include intensity, pulse width, time delay from the beginning
time of the laser irradiation, and frequency spectrum to
measure the pressure wave characteristics in the photon
propagation medium 210, reflecting the acoustic pressure

5 characteristics generated from the photoacoustic generative

array 203. Exemplary electrical signals 212 include peak-
to-peak amplitude of the propagating pressure wave packet,


US 11,193,914 B2

1
PHOTOACOUSTIC PHOTON METER AND
PROCESS FOR MEASURING PHOTON
FLUENCE

CROSS REFERENCE TO RELATED
APPLICATIONS

The application claims priority to U.S. Provisional Patent
Application Ser. No. 62/798,104 filed Jan. 29, 2019, the
disclosure of which is incorporated herein by reference in its
entirety,

STATEMENT REGARDING FEDERALLY
SPONSORED RESEARCH

This invention was made with United States Government
support from the National Institute of Standards and Tech-
nology (NIST), an agency of the United States Department
of Commerce. The Government has certain rights in the
invention. Licensing inquiries may be directed to the Tech-
nology Partnerships Office, NIST, Gaithersburg, Md.,
20899; voice (301) 301-975-2573; email tpo@nist.gov; ref-
erence Ser. No. 16/774,646.

BRIEF DESCRIPTION

Disclosed is a photoacoustic photon meter comprising: a
photoacoustic generative array comprising a plurality of
carbon nanotubes disposed in a photoacoustic generating
pattern, such that the carbon nanotubes: receive photons
comprising optical energy, and produce thermal energy from
the optical energy; and a superstratum comprising a ther-
mally expandable elastomer on which the photoacoustic
generative array is fixedly disposed in position on the

superstratum to spatially conserve the photoacoustic gener- 3

ating pattern, and such that the superstratum: is optically
transparent to the photons; receives the thermal energy from
the photoacoustic generative array; expands and contracts in
response to receipt of the thermal energy; and produces
photoacoustic pressure waves in response to the expansion
and contraction, the photoacoustic pressure waves compris-
ing a photoacoustic intensity and photoacoustic frequency
that are based upon an amount of optical pressure applied to
the carbon nanotubes by the photons, a spatial photon
fluence of the photons, or a spectral photon fluence of the
photons.

Disclosed is a process for measuring photon fluence with
a photoacoustic photon meter, the process comprising:
receiving photons by the carbon nanotubes in the photoa-
coustic generative array disposed on the superstratum; pro-
ducing, by the carbon nanotubes, thermal energy from the
optical energy of the photons; receiving, by the superstra-
tum, the thermal energy from the photoacoustic generative
array; expanding and contracting, by the superstratum, in
response to receiving the thermal energy: and producing, by
the superstratum, photoacoustic pressure waves in response
to expanding and contracting of the superstratum to measure
the photon fluence of the photons received by the photoa-
coustic photon meter, wherein the photoacoustic pressure
waves comprise a photoacoustic intensity and photoacoustic
frequency that are based upon an amount of optical pressure
applied to the carbon nanotubes by the photons, a spatial
photon fluence of the photons, or a spectral photon fluence
of the photons.

Disclosed is a process for measuring a local temperature
rise with a photoacoustic photon meter, the process com-
prising: receiving photons by the carbon nanotubes in the

0

0

30

40

&

3

2

photoacoustic generative array deposited on a plurality of
electrical conductors that is in thermal contact at the inter-
face; increasing a temperature of the photoacoustic genera-
tive array upon receiving photons by the carbon nanotubes;
measuring an electrical voltage across a first pair of electri-
cal conductors of the plurality of electrical conductors while
applying an electrical current across a second pair of elec-
trical conductors of the plurality of electrical conductors;
producing a current versus voltage curve from the electrical
voltage and the electrical current; determining the electrical
resistance from the current versus voltage curve; and obtain-
ing the local temperature change from temperature-depen-
dent electrical conductivity changes.

BRIEF DESCRIPTION OF THE DRAWINGS.

The following description should not be considered lim-
iting in any way. With reference to the accompanying
drawings, like elements are numbered alike.

FIG. 1 shows a perspective view of a photoacoustic
photon meter;

FIG. 2 shows a plan view of a photoacoustic photon
meter;

FIG. 3 shows a cross-section of the photoacoustic photon
meter;

FIG. 4 shows a photoacoustic photon meter;

FIG. 5 shows a plurality of photoacoustic photon meters;

FIG. 6 shows a plurality of photoacoustic photon meters;

FIG. 7 shows a photoacoustic photon meter configured as
a resolution target, wherein panel A shows a scanning
electron micrograph of the photoacoustic photon meter array
before transfer to a superstratum; and panel B shows a
photoacoustic microscope image mapping photoacoustic
pressure from the array that was detected by a photoacoustic
transducer in the reflective position:

FIG. 8 panel A shows a plurality of photoacoustic gen-
erative arrays on a support substrate before transfer to a
superstratum, and, in panel B, a partially expanded view of
a photoacoustic photon meter configured as a fluence target
that includes a plurality of superstrata with individual pho-
toacoustic generative arrays and various photoacoustic gen-
erating patterns of carbon nanotubes:

FIG. 9 shows a plurality of photoacoustic photon meters
configured as a fluence target in panel A; in panel B, an
image of the map of the photoacoustic pressure from the
array, detected by a photoacoustic transducer in the reflec-
tive position: suggestive dimensions of the photon meters in
panel C;

FIG. 10 shows a photoacoustic photon meter configured
for measurement of electrical conductivity or resistance
versus temperature of photoacoustic generative array of
carbon nanotubes under photon fluence irradiation;

FIG. 11 shows a photoacoustic photon meter configured
for measurement of temperature and photon fluence in panel
A; a scanning electron micrograph of the photoacoustic
photon meter without an optical window on the photoacous-
tic photon meter in panel B; an expanded view of the
photoacoustic power meter in panel C; and a graph of
resistance versus temperature for a photoacoustic photon
meter in panel D;

FIG. 12 shows a plurality of superstrata with tunable
optical properties, such as light absorption and/or scattering
properties, for disposition of carbon nanotubes in a photoa-
coustic generative array in a photoacoustic photon meter;

FIG. 13 shows steps in a process for making a photoa-
coustic photon meter that includes initial deposition of a
liquid composition onto a photoacoustic generating pattern


US 11,193,914 B2

Sheet 16 of 20

Dec. 7, 2021

U.S. Patent

9T ‘DIL

<~606

00% —— — |
se
OZ
_
906

( &

(Lv) (240) = d

Peleioued oinsseig puNOseIN

jeLiayeus yeg1e} By] Ul puNos jo paads 1A
ainssaid punosesyn pajyeisuad iq

}aTi€] BUY JO JuaIOIJys09 UO|SUedxa jewel 7d
DLUNJOA Buiquosqe 1YsI{ $,1881e} 1A CLVDA=A &
jetajeu jesuey ayy jo Asuap sd
Jaquosge auj jo AWARSNpuoD jeuayy :49
aseaioui ainjesadwe} Ly

yo sl] BY] 0] BOBLINS BY] LUO1] BOURISIP :Z
79812} ay] JO JUSIYJ800 UaNdiosqe Pn
Adiaua JYyst] pasjnd :0}

Agiaua WY paquosge :e| {ASious 181) 18h pesing jo uondiosoy



US 11,193,914 B2

Sheet 8 of 20

Dec. 7, 2021

U.S. Patent

T

S

%

8 Dl

—— 7

S906

—

(¥)

Ss

B06

£06


US 11,193,914 B2

21

17. The process for measuring photon fluence of claim 16,
further comprising determining, from the electrical signal,
the photon fluence by converting the electrical signal into
the photon fluence of the photons.

18. The process for measuring photon fluence of claim 17,
wherein converting the electrical signal into the photon
fluence of the photons comprises:

subjecting the electrical signal to a pressure conversion

factor to obtain a photoacoustic pressure signal from
the electrical signal; and

normalizing the photoacoustic pressure signal to a fluence

normalization factor to obtain the photon fluence of the
photons.

19. The process for measuring photon fluence of claim 18,
wherein the fluence normalization factor comprises:

By
(@ “Hall's a) .

wherein v, is the speed of sound in the superstratum; B is
a volume expansion coefficient of the superstratum; C,,
is isobaric specific heat of photoacoustic generative
array; |, is an absorption coeflicient of the photoacous-

22

tic generative array of the photoacoustic generating
pattern irradiated by the photons at a position ry at a
wavelength A of photons.
20. A process for measuring a local temperature rise with
5 the photoacoustic photon meter of claim 1, the process
comprising:
receiving photons by the carbon nanotubes in the photoa-
coustic generative array deposited on a plurality of
electrical conductors that is in thermal contact at the
interface;
increasing a temperature of the photoacoustic generative
array upon receiving photons by the carbon nanotubes;
measuring an electrical voltage across a first pair of
electrical conductors of the plurality of electrical con-
ductors while applying an electrical current across a
second pair of electrical conductors of the plurality of
electrical conductors;
producing a current versus voltage curve from the elec-
trical voltage and the electrical current;
determining the electrical resistance from the current
versus voltage curve; and
obtaining the local temperature change from temperature-
dependent electrical conductivity changes.

20

+ * RR Oe


US 11,193,914 B2

15

coustic photon meter 200 in photon propagation medium
210; and subjecting photoacoustic photon meter 200 with
photons 206; absorbing photons 206 by carbon nanotubes
204 arranged as photoacoustic generative array 203; pro-
ducing photoacoustic pressure waves 209 in response to
receiving photons 206 by photoacoustic generative array
203 via receipt of thermal energy 207 by superstratum 201;
receiving photoacoustic pressure waves 209 by photoacous-
tic transducer 211 from photoacoustic pressure waves 209;
producing electrical signal 212 from photoacoustic pressure
waves 209 by photoacoustic transducer 211; and converting
electrical signal 212 to obtain an acoustic pressure P of
thermal energy 207, such that

PE yery. 2) Mra, WO, Hath ¥)

wherein Bv,2/C, is a Griineisen coefficient; 1, (tp A) is an
absorption coefficient of carbon nanotubes 204 in photoa-
coustic generative array 203 of photoacoustic photon meter
200; and @ (11',(typ *)s Meaty 4) is'a photon fluence (energy
per unit area), wherein 4", (ty 2) is a reduced scattering
coefficient of the photon propagating medium: 11, (ty. A) is
an absorption coefficient of the photon propagating medium,
and 2 is a wavelength of pulsed photons 206.
Photoacoustic photon meter 200 and processes disclosed
herein have numerous beneficial uses, including accurate

measurement of photon fluence in a turbid medium, accurate 3

performance testing of photoacoustic transducers, develop-
ment of ultrasound sources with controlled pressure char-
acteristics. Photoacoustic photon meter 200 and processes
disclosed herein provide information for a mechanism of
photonic to thermal or mechanical energy conversion.
Advantageously, photoacoustic photon meter 200 over-
comes limitations of technical deficiencies of conventional
compositions and conventional articles such as a lack of
conventional measurement technologies and standards that
provide accurate local photon fluence, temperature, and
pressure measurements in turbid media. In a light-diffusing
or light-absorbing material, accurate local photon fluence
measurement is challenging. In a turbid medium, scattered
photons dominate and the photon fluence is heterogeneous
in the bulk due to variations in the local intensity and
scattering angle of the photons. Conventional photon detec-
tion sensors such as photomultipliers or photodiodes fail to
accurately measure local photon fluence because of
unknown reflectance at or near the sensor surface and
wavelength-dependent spectral responsivity of the conven-
tional sensor. Moreover, conventional articles are hard to
embed in a bulk material. Photoacoustic photon meter 200
overcomes these limitations and has a known absorption
coefficient that can be selectively fabricated into a desired
shape and disposed in an optically turbid or clear medium or
placed on an exposed surface thereof. Further, photoacoustic
photon meter 200 measures local photon fluence for quan-
titative optical imaging of biological tissues, local tempera-
ture fluctuations in turbid materials during photothermal
therapy that kills tumor cells by light illumination. Photoa-
coustic photon meter 200 can calibrate measurement results
by photonic and optoelectronic devices in a turbid environ-
ment and provide resolution and photon fluence measure-
ment targets. Photoacoustic photon meter 200 can have a
small variation in absorption efficiency across a broad
wavelength range so that photoacoustic photon meter 200
can be a calibration tool for quantitative multispectral mea-

S

2

40

&

16

surements in a variety of optical imaging applications
including optical microscopy, optical coherence tomogra-
phy, photoacoustic microscopy, computed tomography, mul-
tispectral imaging, and the like as well as non-imaging
calibration of an ultrasound transducer or thermometer.
Photoacoustic photon meter 200 and processes herein
unexpectedly measure delivered photon fluence through
photoacoustic pressure. Conventional photon detection sen-
sors such as photomultipliers or photodiodes can be inad-
equate to measure the local photon fluence in a scattering
medium due to unknown reflectance at or near the sensor
surface and wavelength dependent spectral responsivity of a
conventional sensor. Moreover, conventional sensors can be
difficult to embed in a bulk material. Beneficially, photoa-

5 coustic photon meter 200 includes carbon nanotubes with

known absorption coefficient and can be fabricated into a
selected shape that can be disposed in an optically turbid or
clear medium and, upon being illuminated by a pulsed light
source (e.g., laser or light emitting diode, LED), photoa-
coustic photon meter 200 produces photoacoustic pressure
that is detected and used to determine local photon fluence.
Moreover, photoacoustic photon meter 200 provides quan-
titative evaluation of performance of photoacoustic imaging
devices and can be provided in a format such as a resolution

5 target for spatial resolution evaluation or a calibrated spec-

tral response analyzer for quantitative multispectral mea-
surements.

The articles and processes herein are illustrated further by
the following Examples, which are non-limiting,

EXAMPLES
Example 1
Determination of Photoacoustic Pressure

With reference to FIG. 18, photoacoustic photon meter
200 was made by growing CNTs vertically on a silicon
substrate by chemical vapor deposition on patterns pre-
defined by photolithography and transferring the patterned
CNTs to a PDMS substrate as described previously. Pho-
toacoustic photon meter 200 included transferred CNT pat-
tes on a PDMS superstratum, wherein patterns were
various shapes that included lines, rectangles, and discs with
various sizes from a few micrometers to a few millimeters.

Photoacoustic photon meter 200 was subjected to photons
206, from which superstratum 201 produced photoacoustic
pressure waves 209. FIG. 18C shows a graph of acoustic
pressure versus time for raw data of photoacoustic pressure
waves 209 from photoacoustic generating pattern 205 upon
irradiating photoacoustic generative array 203 with a single
laser pulse of photons 206 that had wavelength 532 nm,
pulse width 11 ns, and peak pulse energy 20 nJ that were
focused onto a Gaussian spot size of 2.5 um in diameter, a
full width of 1/e maximum of a Gaussian profile. Photoa-
coustic pressure waves 209 were received by a 50 MHz
bandwidth ultrasound transducer as photoacoustic trans-
ducer 211.

Example 2

Simultaneous Determination of Photoacoustic
Pressure and Photon Fluence

Photoacoustic photon meter 200 can be a standard such as
a calibrated spectral response analyzer for quantitative mul-
tispectral measurements or a multispectral radiometer to


US 11,193,914 B2

Sheet 5 of 20

Dec. 7, 2021

U.S. Patent

616é~—
106“

T0é4

Old

606

v

£06

HOS (

£06

fete

0S

806


U.S. Patent Dec. 7, 2021 Sheet 4 of 20

US 11,193,914 B2

200
how
218 q~2ll
206
210
¢
7
209
|
a
203—7* L_] L_J tt} 204
201
+ 202

FIG. 4


US 11,193,914 B2

Sheet 17 of 20

Dec. 7, 2021

U.S. Patent

Topazepoyy

LT Old

348i pasind ayi jo yBuajanem vy
~_ 60% uunipetu ayy jo yusinyja09 UoNduosge : °
LUNIpalu 84} 4o YUa!I1J4909 SuLieyess peonpal : * i

{eave yun jad Agiaua) sduany lyst]

(Qquainiffao) uasiauns9) d=

3a8ie} JNO 3yi jo
quaiaijja0o uolduosqy

ve (UMD Tp eta)


US 11,193,914 B2

Sheet 7 of 20

Dec. 7, 2021

U.S. Patent

wr OOT

a8eu adoasomiyayy nysnoseajaug

0

L Old

G

sul OOT

Sl]
! a l

(@)

¥OE &0E

ydesSaiy(uonse;}3 Buruuess



US 11,193,914 B2

5

lution target 220 that includes secondary substrate 219 for a
light scattering material in which photoacoustic generative
array 203 has carbon nanotubes 204 arranged in a photoa-
coustic generating pattern 205, wherein photoacoustic gen-
erating pattern 205 is discontinuous so that the photoacous-
tic generating pattern 205 includes a plurality of non-
continuous pattern 213 as shown in FIG. 7.

With reference to FIG. 8 and FIG. 9, photoacoustic photon
meter 200 configured as a fluence target 221 includes a
plurality of photoacoustic generative arrays 203 that include
individual photoacoustic generating patterns 205. Here, each
photoacoustic generative array 203 is individually disposed
on a separate superstratum 201 (e.g., 201.1, 201.2, 201.3),
wherein the superstrata (201.1, 201.2, 201.3) are stacked
together to form layers of photoacoustic generating pattern
205 (205.1, 205.2, 205.3). Here, first superstratum 201.1 and
first photoacoustic generative array 203.1 are stackedly
disposed on second superstratum 201.2 and second photoa-
coustic generative array 203.2 that is stackedly disposed on
third superstratum 201.3 and third photoacoustic generative
array 203.3. Although three stacked photoacoustic generat-
ing pattern (205.1, 205.2, 205.3) are shown in FIG. 8 and
FIG. 9, a number of stacked layers of photoacoustic gen-
erative arrays 203 disposed on superstratum 201 is arbitrary
and can be selected to obtain a selective fluence target
design. Further, photoacoustic photon meter 200 can include
additional layers of superstratum 201 (e.g., 201.4, 201.5).

In an embodiment, with reference to FIG. 10, photoa-
coustic photon meter 200 includes a pattern of a thin film of

an electrical conductor 215.1 and 215.2 with disposed 3

photoacoustic generative array 203 in contact with its top.
Additional electrical conductors 215 (¢.g., 215.3, 215.4) can
be included in photoacoustic photon meter 200. In this
manner, photoacoustic photon meter 200 can be configured

for measuring an electrical resistance across the electrode 3

with the photoacoustic generative array 203 on top. Here,
voltage meter 222 can be connected to third electrical
conductor 215.3 and fourth electrical conductor 215.4, and
current source 223 can be connected to one end of first
electrical conductor 215.1 and the other end of second
electrical conductor 215.2 so that photoacoustic generative
array 203 can be subjected to photons 206, e.g., from light
source 218 in response to which superstratum 201 produces
photoacoustic pressure waves 209 that are received by
photoacoustic transducer 211. In response to receipt of
photoacoustic pressure waves 209, photoacoustic transducer
211 produces electrical signal 212 that is used to determine
photon fluence of photons 206 from light source 218.
Moreover, electrical resistance of photoacoustic generative
array 203 can be obtained by measuring an electrical voltage
while applying an electrical current across electrical con-
ductors 215.1 and 215.2, the electrical resistance can be
calculated from the current versus voltage curve then the
local temperature change information can be obtained from
the temperature dependent electrical resistance change.
Photoacoustic photon meter 200 includes superstratum
201 on which photoacoustic generative array 203 is formed
or disposed. Superstratum 201 can include elastomeric poly-
mers including poly(dimethylsulfoxide) (PDMS), poly(vi-
nyl chloride) plastisol (PVCP), poly-methyl-methacrylate,
polystyrene, polyethylene, high-density _ polyethylene
(HDPE), medium-density polyethylene, low-density poly-
ethylene, and ultrahigh molecular weight polyethylene to
absorb full or partial irradiated photon energy and to convert
absorbed photon energy into heat and then to induce
mechanical expansion and contraction thereof. Superstratum
201 can include an elastomeric polymer as a base material

S

2

40

&

3

6

and additives disposed in the base material. Exemplary
superstrata 201 include thermally expandable elastomer 202
such as PDMS with a high thermal expansion coefficient for
effective conversion of heat energy into mechanical energy
for expansion and contraction of the material to effectively
generate photoacoustic pressure waves. A thickness of
superstratum 201 can be from 100 nm to 10 cm. The
Young’s modulus and thermal expansion coefficient of
superstratum 201 can be from 1000 kPa to 10000 kPa and
from 1x10~ K~! to 1x10"? KTM, respectively. Accordingly,
superstratum 201 can expand and contract in response to
thermally expandable elastomer 202 being heated either
locally or globally. The specific heat capacity of superstra-
tum 201 can be from 1000 J kg~'K~! to 10000 J kg~"K7!. In

s an embodiment, superstratum 201 includes elastomeric

polymer PDMS with or without additives such as titanium
dioxide nano- and micro-particles and microbeads such as
polystyrene beads or silica beads. It is contemplated that
superstratum 201 can be a composition that includes addi-
tives in the elastomer. Such additives include light scattering
and absorbing nano- and micro-particles such as titanium
dioxide nanoparticles, polystyrene micro beads, silica micro
beads, metal and semiconductor nanoparticles, carbon par
ticles and spheres, carbon nanotubes, and pigment proteins

S such as hemoglobin, cytochrome C, and myoglobin, Such

additives with controlled concentration provide controlled
light absorption and scattering properties. FIG. 12 shows a
plurality of superstrata (201.1, 201.2, .. . , 201.6) that
include thermally expandable elastomer 202 and varying
amounts of an additive that change an optical transparency
of superstratum 201 through optical attenuation at a selected
wavelength or optical fluence.

Superstratum 201 can be formed from liquid composition
226. Liquid composition 226 can include thermally expand-
able elastomer 202 as well as light scattering and absorbing
additives, solvent, and the like nano- and micro-particles
such as titanium dioxide nanoparticles, polystyrene micro
beads, silica micro beads, metal and semiconductor nan-
oparticles, carbon particles and spheres, carbon nanotubes,
and pigment proteins such as hemoglobin, cytochrome C,
and myoglobin to control light scattering and absorbing
properties, other optical properties, photothermal properties,
and mechanical properties. Liquid composition 226 can be
subjected to curing by heating to form a gel or solid

5 superstratum 201. It is contemplated that during formation

of superstratum 201 or thereafter thermally expandable
elastomer 202 can be crosslinked selectively to obtain an
amount of crosslinking in the elastomer of thermally
expandable elastomer 202 to provide a desired expansion
and contraction property such as rigidity, thermal expansion
rate, and the like. In an embodiment, solvents for liquid
composition 226 can include diisopropylamine, chloroform,
tetrahydrofuran, hexanes, cyclohexane, toluene, benzene,
chlorobenzene, methylene chloride, t-butyl alcohol, metha-

5 nol, and ethanol. In an embodiment, diisopropylamine is the

solvent and initiates cross linking.

Secondary substrate 219 can include an identical base
material as included in superstratum 201 and identical
additives to control light scattering and absorbing properties,
other optical properties, photothermal properties, and
mechanical properties and can be an additional substrate to
encapsulate photoacoustic generative array 203 or adjust
optical attenuation properties in the irradiation beam path of
photoacoustic photon meter 200. Optical attenuation can

5 include absorption of photons 206 or scattering of photons

206. In this respect, in FIG. 15, exemplary secondary
substrates 219 can include thermally expandable elastomer


a2 United States Patent

Hwang et al.

US011193914B2

US 11,193,914 B2
Dec. 7, 2021

(10) Patent No.:
(45) Date of Patent:

(54) PHOTOACOUSTIC PHOTON METER AND
PROCESS FOR MEASURING PHOTON
FLUENCE

(71) Applicant: Government of the United States of
America, as represented by the
Secretary of Commerce, Gaithersburg,
MD (US)

(72) Inventors: Jeeseong Hwang, Louisville, CO (US);
Christopher Yung, Louisville, CO
(US); Kimberly Ann Briggman,
Boulder, CO (US); John Henry
Lehman, Boulder, CO (US)

GOVERNMENT OF THE UNITED
STATES OF AMERICA, AS
REPRESENTED BY THE
SECRETARY OF COMMERCE,
Gaithersburg, MD (US)

(73) Assignee:

(*) Notice: Subject to any disclaimer, the term of this,

patent is extended or adjusted under 35
U.S.C. 154(b) by 129 days.

(21) Appl. No.: 16/774,646
(22) Filed: Jan. 28, 2020

(65) Prior Publication Data
US 2020/0240957 Al Jul. 30, 2020
Related U.S. Application Data

(60) Provisional application No. 62/798,104, filed on Jan.

29, 2019.
(51) Int. CL

GOIN 29/22 (2006.01)

COIB 32/158 (2017.01)

GOIN 29/24 (2006.01)
(52) US. CL

cpc GOIN 29/2418 (2013.01); COIB 32/158

(2017.08); GOIN 29/221 (2013.01);
(Continued)

(58) Field of Classification Search
CPC ...sesseeeeeeeee COIB 32/158; GOIN 29/221; GOIN
29/2418; GOIN 2291/02872; GOIN
2291/02881; GOIN 2291/101

(Continued)

(56) References Cited
U.S. PATENT DOCUMENTS

8,811,631 B2* 8/2014 Liu HO4R 23/002
381/164
8,946,683 B2* 2/2015 Rogers B82Y 10/00
257/40

(Continued)
FOREIGN PATENT DOCUMENTS

EP 001909080 Al * 4/2008 GOLI 1/42

Primary Examiner — Jacques M Saint Surin
(74) Attorney, Agent, or Firm — Office of Chief Counsel
for National Institute of Standards and Technology

(57) ABSTRACT

A photoacoustic photon meter includes: a photoacoustic
generative array including carbon nanotubes disposed in a
photoacoustic generating pattern, such that the carbon nano-
tubes: receive photons comprising optical energy, and pro-
duce thermal energy from the optical energy; and a super-
stratum including a thermally expandable elastomer on
which the photoacoustic generative array is fixedly disposed
in position on the superstratum to spatially conserve the
photoacoustic generating pattern, and such that the super-
stratum: is optically transparent to the photons; receives the
thermal energy from the photoacoustic generative array;
expands and contracts in response to receipt of the thermal
energy; and produces photoacoustic pressure waves in
response to the expansion and contraction, the photoacoustic
pressure waves including a photoacoustic intensity and
photoacoustic frequency that are based upon an amount of
optical pressure applied to the carbon nanotubes by the
photons, a spatial photon fluence of the photons, or a spectral
photon fluence of photons.

20 Claims, 20 Drawing Sheets

205 204 208

is

(LBs

xe
a

202—

vant

mS
NO

An

204


U.S. Patent Dec. 7, 2021 Sheet 10 of 20 US 11,193,914 B2

Ibo
IS

a
~
he

215.1 &.

200
2151 :
204 Lp, 2162 vor
216.1 yo
204 203
202

V: voltage between the inner probes

T: Current through the outer probes

RW) = ve : electrical resistance

FIG. 10


U.S. Patent Dec. 7, 2021 Sheet 9 of 20 US 11,193,914 B2

(C)
2.5m

5mm

FIG. 9

(B)



US 11,193,914 B2

19

cially in the context of the following claims) are to be
construed to cover both the singular and the plural, unless
otherwise indicated herein or clearly contradicted by con-
text. “Or” means “and/or.” It should further be noted that the
terms “first,” “second,” “primary,” “secondary,” and the like
herein do not denote any order, quantity, or importance, but
rather are used to distinguish one element from another. The
modifier “about” used in connection with a quantity is
inclusive of the stated value and has the meaning dictated by
the context (e.g., it includes the degree of error associated
with measurement of the particular quantity). The conjunc-
tion “or” is used to link objects of a list or alternatives and
is not disjunctive; rather the elements can be used separately
or can be combined together under appropriate circum-
stances.

What is claimed is:

1. A photoacoustic photon meter comprising:

a photoacoustic generative array comprising a plurality of
carbon nanotubes disposed in a photoacoustic generat-
ing pattern, such that the carbon nanotubes:
receive photons comprising optical energy, and
produce thermal energy from the optical energy; and

a superstratum comprising a thermally expandable elas-
tomer on which the photoacoustic generative array is
fixedly disposed in position on the superstratum to
spatially conserve the photoacoustic generating pattern,
and such that the superstratum:
is optically transparent to the photons;

receives the thermal energy from the photoacoustic 3

generative array;

expands and contracts in response to receipt of the
thermal energy; and

produces photoacoustic pressure waves in response to

the expansion and contraction, the photoacoustic 3

pressure waves comprising a photoacoustic intensity
and photoacoustic frequency that are based upon an
amount of optical pressure applied to the carbon
nanotubes by the photons, a spatial photon fluence of
the photons, or a spectral photon fluence of the
photons.

2. The photoacoustic photon meter of claim 1, further

comprising:

a photon propagation medium disposed on the superstra-
tum and in photoacoustic communication with the
superstratum and that:
receives the photoacoustic pressure waves from the

superstratum; and
communicates the photoacoustic pressure waves
through the photon propagation medium.

3. The photoacoustic photon meter of claim 2, further

comprising:
a photoacoustic transducer in photoacoustic communica-
tion with the photon propagation medium and the
superstratum and that:
receives the photoacoustic pressure waves from the
photon propagation medium: and

produces electrical signal from the photoacoustic pres-
sure waves and from which the optical fluence of the
photons can be determined.

4. The photoacoustic photon meter of claim 3, further

comprising:

a plurality of electrical conductors disposed on the super-
stratum with the photoacoustic generative array depos-
ited on the electrical conductors, such that the electrical
conductors are in thermal contact with the photoacous-
tic generative array.

S

2

50

35

65

20

5. The photoacoustic photon meter of claim 3, further
comprising a photodetector in optical communication with
the photoacoustic generative array and the superstratum and
that receives photons transmitted through the photoacoustic
generative array and the superstratum.

6. The photoacoustic photon meter of claim 1, wherein the
photoacoustic generating pattern is discontinuous so that the
photoacoustic generating pattern comprises a plurality of
laterally or axially non-contacting portions.

7. The photoacoustic photon meter of claim 1, wherein the
photoacoustic generating pattern is continuous in an absence
of a discontinuity among the carbon nanotubes in the
photoacoustic generating pattern.

8. The photoacoustic photon meter of claim 1, wherein the
carbon nanotubes are aligned with respect to each other.

9. The photoacoustic photon meter of claim 1, wherein the
carbon nanotubes are randomly arranged or bundled with
respect to each other.

10. The photoacoustic photon meter of claim 1, wherein
the carbon nanotubes in the photoacoustic generating pattern
are arranged spatially and provide different portions of the
photoacoustic generating pattern to have a different optical
absorption coefficient 1, and reduced scattering coefficient
Ta

11. The photoacoustic photon meter of claim 1, wherein
the thermally expandable elastomer comprises polydimeth-
ylsiloxane.

12. The photoacoustic photon meter of claim 2, wherein
the photon propagation medium comprises water.

13. The photoacoustic photon meter of claim 3, wherein
the photoacoustic transducer comprises a hydrophone.

14. A process for measuring photon fluence with the
photoacoustic photon meter of claim 1, the process com-
prising:

receiving photons by the carbon nanotubes in the photoa-

coustic generative array disposed on the superstratum;
producing, by the carbon nanotubes, thermal energy from
the optical energy of the photons;

receiving, by the superstratum, the thermal energy from

the photoacoustic generative array;

expanding and contracting, by the superstratum, in

response to receiving the thermal energy; and
producing, by the superstratum, photoacoustic pressure
waves in response to expanding and contracting of the
superstratum to measure the photon fluence of the
photons received by the photoacoustic photon meter,
wherein the photoacoustic pressure waves comprise a
photoacoustic intensity and photoacoustic frequency
that are based upon an amount of optical pressure
applied to the carbon nanotubes by the photons, a
spatial photon fluence of the photons, or a spectral
photon fluence of the photons.
15. The process for measuring photon fluence of claim 14,
further comprising:
receiving, by the photon propagation medium, the pho-
toacoustic pressure waves from the superstratum; and

communicating, by the superstratum, the photoacoustic
pressure waves through the photon propagation
medium.

16. The process for measuring photon fluence of claim 15,
further comprising:

receiving, by the photoacoustic transducer, the photoa-

coustic pressure waves from the photon propagation
medium; and

producing, by the photoacoustic transducer, an electrical

signal from the photoacoustic pressure waves.


US 11,193,914 B2

17

measure wavelength-dependent photon transport in turbid
medium. Here, measured photoacoustic pressure is propor-
tional to a light absorption coefficient of a sample and local
photon fluence irradiated onto the sample. Photon fluence at
an irradiated region can be obtained from measured pressure
signal. For high accuracy, the acoustic pressure signal and
photon fluence are measured simultaneously. With reference
to FIG. 19, light source 218 produces a pulsed laser light as.
photons 206 that propagate through photoacoustic trans-
ducer 211 with an open aperture, allowing for passing the
irradiating light through, at its center. Photons 206 are
received by photoacoustic generative array 203 disposed on
superstratum 201 of photoacoustic photon meter 200 with
known 1,(4) or (1,0). Photoacoustic pressure waves 209
provide photoacoustic pressure generated from a single laser
pulse and that is detected by photoacoustic transducer 211.
Photons 206 irradiated onto photoacoustic photon meter 200
are partially transmitted through photoacoustic photon meter
200 and measured by photodetector 214 disposed opposing
photoacoustic photon meter 200. With known (4) or
(u,'(A), the total fluence irradiated on photoacoustic photon
meter 200 is calculated using the Beer-Lambert law or
another technique. FIG. 18B shows time-traced photoacous-
tic pressure signals obtained from different regions of pho-
toacoustic generative array 203 of photoacoustic photon
meter 200 that had different j1,. FIG. 18C shows a time-
traced photon transmission signal obtained from different
regions of photoacoustic generative array 203 with different
11,. FIG. 19D shows a graph of peak-to-peak pressure signal

versus peak photodiode signal exhibited a transmission 3

increase as photoacoustic signal decreased as photoacoustic
photon meter 200 was translated to an optically darker
region that had a greater 11,

Example 3

CNT-Based Sensor for Simultaneous Temperature
and Fluence Measurements

In photoacoustic photon meter 200, upon irradiation,
absorbed photons increase a local temperature of photoa-
coustic photon meter 200, resulting in change of electrical
resistivity or conductivity of carbon nanotubes 204 in pho-
toacoustic generative array 203. Therefore, photoacoustic
photon meter 200 with photoacoustic generating pattern 205
disposed on superstratum 201 and arranged in a selected
configuration provides a local temperature sensor. Accord-
ingly, photoacoustic photon meter 200 was configured as a
thermistor in an integrated device. Lithography and chemi-
cal vapor deposition (CVD) provided patterning of CNTs on
a micrometer scale on a support. Electrical conductors were
attached to photoacoustic generating pattern 205 to monitor
change in electrical resistivity or conductivity by absorbed
photons from a pulsed light source with measurements made
by a 4-probe measurement technique. FIG. 11 shows a CNT
photoacoustic generating pattern 205 in a photoacoustic
generative array 203 deposited on a silicon or vanadium
oxide substrate configured as a microbolometer for measur-
ing electrical resistivity in response to temperature change.
This device can be modified for photoacoustic measure-
ments by including an optically transparent window below
the CNT pattern for optical transmission measurement and
encapsulation of the device with PDMS superstratum 201
for effective photoacoustic signal generation of photoacous-
tic pressure waves 209 in photon propagation medium 210
such as water. Photoacoustic photon meter 200 can be
water-proofed for resistivity or conductivity measurements.

S

3

40

18

FIG. 19 shows a graph of resistance versus temperature for
vertically aligned CNTs in photoacoustic generative array
203. It should be appreciated that changes in simultaneously
measured ultrasound pressure and electrical resistance or
resistivity with known emission energy of the light source
provide a calibration curve of the fluence versus electrical
conductivity. The fluence versus ultrasound pressure
obtained by the method described can provide a calibration
curve of the fluence versus ultrasound pressure. These two
calibration curves for the pressure, photon fluence, and
electrical conductivity, by inter-relating them, provide for
readily obtaining one value from the others.

Example 4

Dimensional Calibration with a Resolution
Standard

‘A resolution standard was made by vertically growing
CNTs on a silicon wafer by lithography and chemical vapor
deposition technique, followed by transferring the CNT
patterns to the surface of PDMS, where pattern consists of
a group of 2 micrometer width lines and 4 micrometer width
lines, where lines are separated by a 20 micrometer distance.

s. The resolution standard is shown in FIG. 20. The resolution

standard was irradiated with pulsed laser of photons 206 that
had wavelength 532 nm, pulse width 11 ns, and peak pulse
energy 20 nJ that were focused onto a Gaussian spot size of
2.5 jum in diameter. Photoacoustic pressure waves 209 were
received by a 50 MHz bandwidth ultrasound transducer as
photoacoustic transducer 211 while raster scanning the
sample to produce a 2D photoacoustic pressure signal image
shown in FIG. 20(A), and from this image intensity profiles
along the indicated lines over the image were plotted in FIG.

20(B). This can be used to calibrate the raster scanner and.
determine the resolution of the phoatoacoustic imaging
device.

While one or more embodiments have been shown and
described, modifications and substitutions may be made
thereto without departing from the spirit and scope of the
invention. Accordingly, it is to be understood that the present
invention has been described by way of illustrations and not
limitation. Embodiments herein can be used independently
or can be combined.

All ranges disclosed herein are inclusive of the endpoints,
and the endpoints are independently combinable with each
other. The ranges are continuous and thus contain every
value and subset thereof in the range. Unless otherwise
stated or contextually inapplicable, all percentages, when
expressing a quantity, are weight percentages. The suflix
“(s)” as used herein is intended to include both the singular
and the plural of the term that it modifies, thereby including
at least one of that term (e.g. the colorant(s) includes at least
one colorants). “Optional” or “optionally” means that the
subsequently described event or circumstance can or cannot
occur, and that the description includes instances where the
event occurs and instances where it does not. As used herein,
“combination” is inclusive of blends, mixtures, alloys, reac-
tion products, and the like.

As used herein, “a combination thereof” refers to a
combination comprising at least one of the named constitu-
ents, components, compounds, or elements, optionally
together with one or more of the same class of constituents,
components, compounds, or elements.

All references are incorporated herein by reference.

The use of the terms “a” and “an” and “the” and similar
referents in the context of describing the invention (espe-


U.S. Patent Dec. 7, 2021 Sheet 6 of 20 US 11,193,914 B2

Resolution Target
205,

208 Fluence Target 201

FIG. 6


US 11,193,914 B2

Sheet 20 of 20

Dec. 7, 2021

U.S. Patent

06 “DIA

{sjoxid) A

(nv) Aususn vd

saul] Suipuodsa02 ay} Buoje sapijoud Ajisuaquy

(D)

(Vv)


US 11,193,914 B2

11

pulse width of the wave packet, and the delay time between
the pulse irradiation time and the signal arrival time, and the
like.

According to an embodiment, e.g., as shown in FIG. 10
and FIG. 19, photoacoustic photon meter 200 includes
electrical conductor 215 with photoacoustic generative array
203 in contact with electrical conductor 215 to provide
thermal energy from photoacoustic generative array 203 to
electrical conductor 215 upon light irradiation onto photoa-
coustic generative array 203. Electrical conductor 215 can
include photo lithographically patterned thin metal or metal
oxide films to measure an electrical conductivity across the
electrode with photoacoustic generative array 203 on top
while irradiating a pulsed light onto photoacoustic genera-
tive array 203 and can be a thin film gold, silver, tungsten,
titanium, indium tin oxide, silicon nitride, or silicon oxide.
Exemplary electrical conductors 215 include a thin firm of
indium tin oxide, tungsten, titanium oxide and the like. In an
embodiment, electrical conductor 215 includes a tungsten
thin film.

Electrical conductor 215 can be in contact with photoa-
coustic generative array 203 on its top for electrical equip-
ment or circuitry to provide electrical measurement of
electrical conductance or resistance change across electrical
conductor 215 when photoacoustic generative array 203 is
irradiated by a pulsed laser increasing local temperature of
electrical conductor 215, while current is supplied across the
electrical conductor 215. Electrical equipment includes volt-

age meter 222 to measure voltage across electrical conductor 3

215, current source 223 to provide electrical current to
electrical conductor 215 with photoacoustic generative array
203 on its top. Electrical resistance of photoacoustic gen-
erative array 203 can be determined with such devices

configured as shown in FIG. 10, Here, when photons 206 are 3

received by photoacoustic generative array 203, electrical
resistance can decrease as photoacoustic generative array
203 provides heat to electrical conductor 215 to increase its
temperature by heat transfer from the heated photoacoustic
generative array 203.

Photoacoustic photon meter 200 can be made in various
ways. In an embodiment, with reference to FIG. 13 and FIG.
14, a process for making photoacoustic photon meter 200
includes forming photoacoustic generative array 203 on
support substrate 224; disposing support substrate 224 that
includes photoacoustic generative array 203 disposed
thereon in container 225 (e.g., a mold or petri dish); dispos-
ing liquid composition 226 on photoacoustic generative
array 203 in container 225; solidifying liquid composition
226 to form superstratum 201; and transferring, from sup-
port substrate 224, photoacoustic generative array 203 to
superstratum 201 to make photoacoustic photon meter 200.
With reference to FIG. 5, the process for making photoa-
coustic photon meter 200 can include further forming sec-
ondary substrate 219 on superstratum 201 such that photoa-
coustic generative array 203 is interposed between
superstratum 201 and secondary substrate 219.

Forming photoacoustic generative array 203 on support
substrate 224 can include drop casting a solution containing
carbon nanotubes and drying, spin casting a solution con-
taining carbon nanotubes and drying, transferring carbon
nanotubes from an aqueous solution, and chemical vapor
depositing carbon nanotubes with photolithographic pattern-
ing. The last approach includes photolithography in which a
photoresist defines a range of patterns for selective deposi-
tion of a surface catalyst followed by lift-off of the photo-
resist to leave a pattern of catalyst coating on the support

S

8

2

3

12

substrate, and growing carbon nanotubes using chemical
vapor deposition selectively on the catalyst pattern.

Solidifying liquid composition 226 to form superstratum
201 can include a volume of liquid elastomeric solution
included with curing reagent, wherein diisopropylamine, is
poured into a petri dish that contains support substrate 224
with photoacoustic generative array 203 attached on the
bottom surface of the container by an epoxy glue. The petri
dish can be heated at 75° C. for 4-6 hours to solidify the
liquid elastomeric polymer.

Transferring, from support substrate 224, photoacoustic
generative array 203 to superstratum 201 can include oven
baking, then removing the solidified elastomeric polymer
out of the container and transferring photoacoustic genera-
tive array 203 from the surface of the support substrate 224
onto the bottom surface of superstratum 201.

Forming secondary substrate 219 on superstratum 201 can
include, after inverting superstratum 201, disposing super-
stratum 201 in another container with the transferred pho-
toacoustic generative array 203 on its top surface, pouring a
volume of liquid elastomeric solution included with curing
reagent thereon, and optionally repeating the process for
solidifying liquid composition 226 to form superstratum 201
and transferring, from support substrate 224, photoacoustic
generative array 203 to superstratum 201.

The process for making photoacoustic photon meter 200
also can include the addition of light scattering or absorbing
additives including nano- and micro-particles such as tita-
nium dioxide nanoparticles, polystyrene micro beads, silica
micro beads, metal and semiconductor nanoparticles, carbon
particles and spheres, carbon nanotubes, and pigment pro-
teins such as hemoglobin, cytochrome C, and myoglobin.
Inclusion of additives can be performed as follows. Addi-
tives are dispersed into a solvent, mixed with elastomeric
polymer liquid, and thoroughly dispersed in the polymer
liquid. The solvent is evaporated by degassing, heat can be
applied. A curing reagent is added to initiate solidification.
A volume of this final composition is poured into container
and degassed in a vacuum chamber. The process can be
repeated for solidifying liquid composition 226 to form
superstratum 201 and transferring, from support substrate
224, photoacoustic generative array 203 to superstratum
201

‘A process for process for measuring photon fluence with
photoacoustic photon meter 200 can include the following,
The experimentally measured photoacoustic pressure is pro-
portional to the light absorption coefficient of the sample and
local photon fluence irradiated onto the sample as follows:

Be ,
Ge eats A)-O(ry HA), Halts AD)

Here, v, is the speed of sound in a medium; B is a volume
expansion coefficient; C,, is an isobaric specific heat capac-
ity; a is an absorption coefficient at the irradiated target
position (r;) at wavelength (2.) of the pulsed light: @ is
photon fluence (the number of irradiated photons per unit
area of the target) that depends on the beam path (ry,) of the
photons in the medium, wavelength-dependent reduced scat-
tering coefficient (11,4) of the medium through which the
photons are transported before reaching the target, and
wavelength and photon path-dependent absorption coefli-
cient (1,(typ 4) of the medium. With known vs, B, Cp, and
na, the photon fluence at the irradiated region can be
obtained from the experimentally measured pressure signal


U.S. Patent Dec. 7, 2021 Sheet 2 of 20 US 11,193,914 B2

200

205

204

FIG. 2


U.S. Patent Dec. 7, 2021 Sheet 13 of 20 US 11,193,914 B2

FIG. 18



U.S. Patent Dec. 7, 2021 Sheet 15 of 20 US 11,193,914 B2

(B)

229
FIG. 15

A bs

5
228

227~— Te

(A)
210~ f° *


U.S. Patent Dec. 7, 2021 Sheet 1 of 20 US 11,193,914 B2

204 205 204 204 203

204

202 201

FIG. 1


US 11,193,914 B2

7

202, light attenuator 227 (e.g., an absorber, a scatterer, and
the like), optical matrix 228, or the like. A thickness of
secondary substrate 219 can be from 100 nm to 10 cm. The
Young’s modulus and thermal expansion coefficient of sec-
ondary substrate 219 can be from 1000 kPa to 10000 kPa
and from 1x10 K~! to 1x107? K~', respectively. Accord-
ingly, secondary substrate 219 can expand and contract in
response to thermally expandable elastomer 202 being
heated either locally or globally. The specific heat capacity
of secondary substrate 219 can be from 1000 J kg'K7! to
10000 J kg~'K~!. In an embodiment, secondary substrate
219 includes elastomeric polymers including PDMS, PVCP,
poly-methyl-methacrylate, polystyrene, polyethylene, high-
density polyethylene (HDPE). medium-density polyethyl-
ene, low-density polyethylene, and ultrahigh molecular
weight polyethylene and not limited to these listed elasto-
meric polymeric materials. PDMS, PVCP or HDPE can be
the base material. It is contemplated that secondary substrate
219 can be a composition that includes additives in the
elastomer. Such light scattering and absorbing additives
include nano- and micro-particles such as titanium dioxide
nanoparticles, polystyrene micro beads, silica micro beads,
metal and semiconductor nanoparticles, carbon particles and
spheres, carbon nanotubes, and pigment proteins such as
hemoglobin, cytochrome C, and myoglobin. Such additives
with controlled concentration provide controlled light
absorption and scattering properties.

Photoacoustic generative array 203 can be formed on
support substrate 224 before transferring photoacoustic gen-

erative array 203 to superstratum 201 from support substrate 3

224 to form photoacoustic photon meter 200. Support sub-
strate 224 can include a flat or curved solid or gel material
onto which carbon nanotubes in sub-micrometer or microm-
eter scale patterns can be grown or deposited including

materials such as silicon, quartz, calcium fluoride, magne- 3

sium fluoride, glass, Teflon, glass coated with metals includ-
ing indium tin oxide, gold, aluminum, titanium, elastomeric
polymers. Exemplary support substrates 224 include a sili-
con wafer, polished metal substrate, optical flat window, and
the like. Moreover, support substrate 224 have stable ther-
mal and chemical properties to enable photolithography or
electron beam lithography patterning of carbon nanotubes
catalyst and subsequent growth of carbon nanotubes by
chemical vapor deposition technique. A thickness of support
substrate 224 can be from 100 micrometer to 1 centimeter.
The Young’s modulus of support substrate 224 can be from
10 GPa to 200 GPa. In an embodiment, support substrate
224 includes silicon wafer, quartz, magnesium fluoride, and
calcium fluoride substrates.

Carbon nanotubes 204 can include multi wall, single wall,
metallic, semiconductor carbon nanotubes of one or more of
these types that can have different electrical, mechanical,
thermal, or optical properties including electrical conduc-
tivity, peak absorption wavelength, specific heat capacity,
light absorption and scattering properties. Carbon nanotubes
204 can be vertically grown by chemical vapor deposition,
homogenously dispersed carbon nanotubes in elastomeric
polymer, or carbon nanotubes transferred from a water
surface to a solid substrate. Exemplary carbon nanotubes
204 include metallic single wall, metallic multiwall, semi-
conductor single wall, semiconductor multiwall carbon
nanotubes and the like. An aspect ratio of individual carbon
nanotubes 204 can be from 10 to 1000000, specifically from
100 to 2000. Carbon nanotubes 204 can be modified to
include a substitute atom in the body of the carbon nanotube,
such that a substitute atom replaces a carbon atom in the
body of the carbon nanotube. Exemplary substitute atoms

2

40

&

8

include boron, nitrogen, silicon, and the like. Carbon nano-
tubes 204 can include a functional group attached to an
atom, e.g., a carbon atom or substitute atom. Exemplary
functional groups include carboxyl, amine, hydroxyl, and
the like. In an embodiment, carbon nanotubes 204 includes
metallic multiwalled carbon nanotubes vertically grown on
a silicon substrate by chemical vapor deposition or photog-
raphy patterning.

Carbon nanotubes 204 are disposed in photoacoustic
generative array 203 and arranged in photoacoustic gener-
ating pattern 205 that produces spatially selective heating of
superstratum 201 over a desired period of time. Photoacous-
tic generating pattern 205 includes a shape formatted to
selectively create photoacoustic pressure waves 209 from
specific regions of superstratum 201. Exemplary shapes of
photoacoustic generating pattern 205 are relative to a surface
of superstratum 201 on which carbon nanotubes 204 are
disposed in desired patterns including linear, round, spiral,
interdigitated, polygonal, and the like. Photoacoustic gen-
erating pattern 205 can be discontinuous such that gaps
occur between adjacent patterns of carbon nanotubes 204
with a plurality of non-contacting portions 213 of carbon
nanotubes 204 (see, e.g.. FIG. 7) or can be continuous (see,
eg. FIG. 19A) so that adjacent patterns or portions of
carbon nanotubes 204 are in physical contact. Photoacoustic
generating pattern 205 can be continuous in an absence of a
discontinuity among carbon nanotubes 204. A pitch, i.e. a
distance of separation, between adjacent parts of photoa-
coustic generative array 203 can be selected to achieve
thermal heating rate or thermal heating area of superstratum
201 in response to receipt of photons 206 by carbon nano-
tubes 204. The pitch can be from 100 nanometers to 10
millimeters.

It is contemplated that photoacoustic generative array 203
can include a plurality of photoacoustic generating patterns
205, e.g., as shown in FIG. 7. Further, photoacoustic gen-
erative array 203 can include a plurality of different types of
carbon nanotubes 204, including a combination of modified
carbon nanotubes (¢.g., including a substitute atom or func-
tional group), aspect ratios, and the like. It is contemplated
that carbon nanotubes 204 in photoacoustic generative array
203 can be aligned with respect to each other so that carbon
nanotubes 204 are aligned at a selected angle with respect to
the surface of superstratum 201 on which photoacoustic
generative array 203 is disposed to provide, e.g., vertically
aligned or bundled carbon nanotubes and the like. Carbon
nanotubes 204 can be randomly arranged with respect to
each other. Moreover, carbon nanotubes 204 in the photoa-
coustic generating pattern 205 can be arranged spatially and
provide different portions of photoacoustic generating pat-
tern 205 to have a different optical absorption coefficient j1,
and reduced scattering coefficient 1,'. After patterning, the
carbon nanotubes can be exposed to a gas plasma to make
the carbon nanotubes bundled; such processing changes
optical properties of the carbon nanotubes such as absorp-
tion and scattering or reduced scattering coefficients.

Light source 218 produces photons 206. Light source 218
can include a pulsed laser, intensity modulated continuous
laser, pulsed light emitting diode, intensity modulated light
emitting diode, and frequency comb laser that produces
photons 206 having a wavelength from ultraviolet to mid
infrared to provide optical energy to carbon nanotubes 204
that absorb light and convert light energy into heat that is
subsequently converted to photoacoustic pressure. Light
source 218 can include light delivery or light modification
components such as an optical fiber, lens, frequency doubler,
frequency tripler, frequency quadrupler, and the like. Exem-


US 11,193,914 B2

Page 2
(52) US.CL
CPC verses GOIN 2291/02872 (2013.01); GOIN
2291/0281 (2013.01); GOIN 2291/101
(2013.01)

(58) Field of Classification Search
USPC veecsetesestseessneeessneesssneesseseeesssneesssnes 73/643
See application file for complete search history.
(56) References Cited
U.S. PATENT DOCUMENTS

9,759,689 B2 9/2017 Guo
10,725,373 BI* 7/2020 Kumar GO3F 7/0002

* cited by examiner


US 11,193,914 B2

13

For high accuracy, the pressure signal and photon fluence
can also be measured simultaneously. This is achieved by an
experimental configuration demonstrated in FIG. 19. A
pulsed laser light is irradiated through a photoacoustic
transducer with a clear hole, passing the irradiating light
through, at the center and onto photoacoustic generative
array 203 with known ,(4) and/or (1,'(A). Photoacoustic
pressure generated by a single laser pulse is detected by
photoacoustic transducer 211. The photons irradiated onto
the sample is partially transmitted through the sample which
is measured by photodetector 214 placed on the opposite
side. With known 1,0.) and/or (110), the total fluence
irradiated onto the sample can be back calculated by the
Beer-Lambert law and/or other relevant techniques. With
reference to FIG. 19, a plot of peak to peak pressure signal
vs the peak photodiode signal exhibits the transmission
increases as the photoacoustic signal decreases when the
sample is translated to optically darker region due to increas-
ing 1,

Photoacoustic photon meter 200 has numerous advan-
tages and unexpected benefits and uses. In an embodiment,
a process for measuring photon fluence with photoacoustic
photon meter 200 includes: receiving photons 206 by carbon
nanotubes 204 in photoacoustic generative array 203 dis-
posed on superstratum 201; producing, by carbon nanotubes
204, thermal energy 207 from optical energy 208 of photons
206; receiving, by superstratum 201, thermal energy 207
from photoacoustic generative array 203; expanding and
contracting, by superstratum 201, in response to receiving

thermal energy 207; and producing, by superstratum 201, 3

photoacoustic pressure waves 209 in response to expanding
and contracting of superstratum 201 to measure photon
fluence of photons 206 received by photoacoustic photon
meter 200, wherein photoacoustic pressure waves 209

include a photoacoustic intensity and photoacoustic fre- 3

quency that are based upon an amount of optical energy
applied to carbon nanotubes 204 by photons 206, a spatial
photon fluence of photons 206, or a spectral photon fluence
of photons 206. The process for measuring photon fluence
further can include receiving, by photon propagation
medium 210, photoacoustic pressure waves 209 from super-
stratum 201; and communicating, by superstratum 201,
photoacoustic pressure waves 209 through photon propaga-
tion medium 210. The process for measuring photon fluence
further can include receiving, by photoacoustic transducer
211, photoacoustic pressure waves 209 from photon propa-
gation medium 210; and producing, by photoacoustic trans-
ducer 211, electrical signal 212 from photoacoustic pressure
waves 209. The process for measuring photon fluence fur-
ther can include determining, from electrical signal 212,
photon fluence by converting electrical signal 212 into the
photon fluence of photons 206.

Converting electrical signal 212 into photon fluence of
photons 206 can include subjecting electrical signal 212 to
a pressure conversion factor to obtain a photoacoustic pres-
sure signal from electrical signal 212; and normalizing the
photoacoustic pressure signal to a fluence normalization
factor to obtain the photon fluence of photons 206. The
fluence normalization factor can include:

By
(

wherein Bv,2/C, is a Griineisen coefficient: 41, (ty, 4) is an
absorption coefficient of carbon nanotubes 204 in photoa-

a1
“Hal a») :

S

3

40

60

6:

14

coustic generative array 203 of photoacoustic photon meter
200; and P(\,(ryp4), He(fxe 4) is a photon fluence (energy
per unit area), wherein ', (ry, A) is a reduced scattering
coeflicient of the photon propagating medium; 1, (ty, %) is
an absorption coefficient of the photon propagating medium,
and 2 is a wavelength of pulsed photons 206.

With reference to FIG, 15, it should be appreciated that
propagation of photons 206 through photon propagation
medium 210 that can be, e.g., a turbid medium, including
optical matrix 228 in which is disposed light attenuator 227
that scatter or absorb certain photons 206, can be received by
analyte volume 229. Photoacoustic photon meter 200 can be
disposed on analyte volume 229 to measure an optical
property, mechanical property, or thermal property by mea-

5 suring photoacoustic pressure. Here, photon fluence analyte

volume 229 is @=dN/dA, wherein dN is the number of
photons 206 entering into a virtual sphere of cross sectional
area dA as shown in FIG. 14B.

It is contemplated that photoacoustic photon meter 200
produces a photoacoustic pressure for detection of local
fluence within an optically turbid or clear medium. Photoa-
coustic photon meter 200 can be disposed in or on the
optically turbid or clear medium. photoacoustic pressure
waves 209 also is referred to as a photoacoustic pressure

5. signal that can be detected by photoacoustic transducer 211

In an embodiment, with reference to FIG. 16, a process for
performing photoacoustic imaging with photoacoustic pho-
ton meter 200 includes disposing photoacoustic photon
meter 200 in photon propagation medium 210; and subject-
ing photoacoustic photon meter 200 with photons 206;
absorbing photons 206 by carbon nanotubes 204 arranged as
photoacoustic generative array 203, such that an amount of
photons 206 absorbed is

Ter
wherein 1, is the amount of absorbed light energy; I, is
irradiating pulsed light energy; 1, is an absorption coefli-
cient of the target, and z is a distance from an exterior
surface of photon propagation medium 210 to photoacoustic
generative array 203 of photoacoustic photon meter 200.
The process of performing photoacoustic imaging also can
include producing thermal energy 207 to locally heat pho-
toacoustic generative array 203 and superstratum 201, such
that a temperature change of superstratum 201 by thermal
energy 207 is

wherein @ is an experimentally determined material-depen-
dent constant, AP is the pressure rise when the temperature
rise by AT. The process of performing photoacoustic imag-
ing also can include thermoelastically expanding superstra-

5 tum 201 in response to receiving thermal energy 207 from

photoacoustic generative array 203, such that the change in
the volume V of superstratum 201 after expansion is V=V,
(BAT). wherein V, is the initial volume, and is a thermal
expansion coeflicient of superstratum 201. The process of
performing photoacoustic imaging also can include con-
tracting superstratum 201 and generating photoacoustic
pressure waves 209 as ultrasound pressure P such that
P=(pv,2) (BAT), wherein v, is the speed of sound in the
photon propagation medium 210.

In an embodiment, with reference to FIG. 16, a process
for determining photon fluence and acoustic pressure with
photoacoustic photon meter 200 includes disposing photoa-


US 11,193,914 B2

Sheet 11 of 20

Dec. 7, 2021

U.S. Patent

Tt ‘Old

(3) aunqgevedweay

OOF OS¢ O02 OST GOL ag a
: 10

ot

oT

©
=
{(SiuyQ) aauesisay

Ot

100

Ayisuap yseso} Buiseaioag | (@

BISBUL M\ Pele}eipioy

Wy)


US 11,193,914 B2

Sheet 14 of 20

Dec. 7, 2021

U.S. Patent

PI Dla

606 £06
\ ¥0% Bulino

owe + © — tou/SWdd ppe

1 eememeememme Byun

e 606
\.

POG
) = a Jajsuely
102 >a
“
‘\oog
(@ / W) 98%
208