Action spectroscopies use a readout created by the action of light on the molecules or material rather than optical absorption. Ultrafast 2D photocurrent and 2D fluorescence spectroscopies are two such action spectroscopies. Despite their utility, multidimensional action spectroscopies suffer from a background created by incoherent population mixing. These backgrounds appear when the action of one molecule impacts that of another, creating a signal that mimics a fourth-order population response but is really just the convolution of two linear responses. The background created by incoherent mixing is often much larger than the desired foreground signals. In this paper, we describe the physical mechanisms that give rise to the incoherent signals, drawing Feynman paths for each. There are three variations of incoherent signals, differing by their pulse ordering. They all have the same phase dependence as the desired fourth-order population signals and so cannot be removed by standard phase cycling, but they do differ in their polarization responses and dephasing times. We propose, and implement, a spectrometer design that eliminates the background signals for isotropically oriented samples, leaving only the desired fourth-order 2D action spectra. Our spectrometer utilizes a TWINS interferometer and a pulse shaper interferometer, each driven with a different white-light source so that the pulse pairs within each interferometer are phase stable, but not between the two. The lack of phase stability between the two interferometers eliminates two of the three incoherent responses. The third incoherent response is eliminated with the polarization scheme ⟨0, π/2, π/4, π/4⟩. Our spectrometer also enables both 2D photocurrent and 2D white-light spectra to be collected simultaneously, thereby enabling a direct comparison between action and optical detection under identical conditions and at the exact same position on the sample. Using this spectrometer and photovoltaic devices made from thin films of semiconducting carbon nanotubes, we demonstrate 2D photocurrent spectra free of incoherent background.

1.
P.
Hamm
,
M.
Lim
, and
R. M.
Hochstrasser
, “
Structure of the amide I band of peptides measured by femtosecond nonlinear-infrared spectroscopy
,”
J. Phys. Chem. B
102
,
6123
6138
(
1998
).
2.
J.
Hybl
,
A.
Albrecht
,
S.
Gallagher Faeder
, and
D.
Jonas
, “
Two-dimensional electronic spectroscopy
,”
Chem. Phys. Lett.
297
,
307
313
(
1998
).
3.
M. C.
Asplund
,
M. T.
Zanni
, and
R. M.
Hochstrasser
, “
Two-dimensional infrared spectroscopy of peptides by phase-controlled femtosecond vibrational photon echoes
,”
Proc. Natl. Acad. Sci. U. S. A.
97
(
15
),
8219
8224
(
2000
).
4.
N.
Demirdoven
,
M.
Khalil
, and
A.
Tokmakoff
, “
Correlated vibrational dynamics revealed by two-dimensional infrared spectroscopy
,”
Phys. Rev. Lett.
89
(
23
),
237401
(
2002
).
5.
C. R.
Baiz
,
B.
Blasiak
,
J.
Bredenbeck
,
M.
Cho
,
J. H.
Choi
,
S. A.
Corcelli
,
A. G.
Dijkstra
,
C. J.
Feng
,
S.
Garrett-Roe
,
N. H.
Ge
et al, “
Vibrational spectroscopic map, vibrational spectroscopy, and intermolecular interaction
,”
Chem. Rev.
120
(
15
),
7152
7218
(
2020
).
6.
M. K.
Petti
,
J. P.
Lomont
,
M.
Maj
, and
M. T.
Zanni
, “
Two-Dimensional spectroscopy is being used to address core scientific questions in biology and materials science
,”
J. Phys. Chem. B
122
(
6
),
1771
1780
(
2018
).
7.
S.
Biswas
,
J.
Kim
,
X.
Zhang
, and
G. D.
Scholes
, “
Coherent two-dimensional and broadband electronic spectroscopies
,”
Chem. Rev.
122
(
3
),
4257
4321
(
2022
).
8.
P.
Hamm
and
M. T.
Zanni
,
Concepts and Methods of 2D Infrared Spectroscopy
(
Cambridge University Press
,
2001
).
9.
P.
Hamm
, “
Principles of nonlinear optical spectroscopy: A practical approach or: Mukamel for dummies
,” https://www.chem.uci.edu/~dmitryf/manuals/Fundamentals/Mukamel%20for%20dummies.pdf,
2005
.
10.
S.
Mukamel
,
Principles of Nonlinear Optical Spectroscopy
(
Oxford University Press
,
1995
).
11.
P. F.
Tekavec
,
G. A.
Lott
, and
A. H.
Marcus
, “
Fluorescence-detected two-dimensional electronic coherence spectroscopy by acousto-optic phase modulation
,”
J. Chem. Phys.
127
(
21
),
214307
(
2007
).
12.
G.
Nardin
,
T. M.
Autry
,
K. L.
Silverman
, and
S. T.
Cundiff
, “
Multidimensional coherent photocurrent spectroscopy of a semiconductor nanostructure
,”
Opt. Express
21
(
23
),
28617
28627
(
2013
).
13.
A. A.
Bakulin
,
C.
Silva
, and
E.
Vella
, “
Ultrafast spectroscopy with photocurrent detection: Watching excitonic optoelectronic systems at work
,”
J. Phys. Chem. Lett.
7
(
2
),
250
258
(
2016
).
14.
S.
Draeger
,
S.
Roeding
, and
T.
Brixner
, “
Rapid-scan coherent 2D fluorescence spectroscopy
,”
Opt. Express
25
(
4
),
3259
3267
(
2017
).
15.
P.
Maly
and
T.
Mancal
, “
Signatures of exciton delocalization and exciton-exciton annihilation in fluorescence-detected two-dimensional coherent spectroscopy
,”
J. Phys. Chem. Lett.
9
(
19
),
5654
5659
(
2018
).
16.
V.
Tiwari
,
Y. A.
Matutes
,
A. T.
Gardiner
,
T. L. C.
Jansen
,
R. J.
Cogdell
, and
J. P.
Ogilvie
, “
Spatially-resolved fluorescence-detected two-dimensional electronic spectroscopy probes varying excitonic structure in photosynthetic bacteria
,”
Nat. Commun.
9
(
1
),
4219
(
2018
).
17.
N.
Zhou
,
J.
Hu
,
Z.
Ouyang
,
O. F.
Williams
,
L.
Yan
,
W.
You
, and
A. M.
Moran
, “
Nonlinear photocurrent spectroscopy of layered 2D perovskite quantum wells
,”
J. Phys. Chem. Lett.
10
(
23
),
7362
7367
(
2019
).
18.
A.
Anda
and
J. H.
Cole
, “
Two-dimensional spectroscopy beyond the perturbative limit: The influence of finite pulses and detection modes
,”
J. Chem. Phys.
154
(
11
),
114113
(
2021
).
19.
L.
Bolzonello
,
F.
Bernal-Texca
,
L. G.
Gerling
,
J.
Ockova
,
E.
Collini
,
J.
Martorell
, and
N. F.
van Hulst
, “
Photocurrent-detected 2D electronic spectroscopy reveals ultrafast hole transfer in operating PM6/Y6 organic solar cells
,”
J. Phys. Chem. Lett.
12
(
16
),
3983
3988
(
2021
).
20.
Z.
Ma
,
L.
Chen
,
C.
Xu
, and
J. A.
Fournier
, “
Two-Dimensional infrared spectroscopy of isolated molecular ions
,”
J. Phys. Chem. Lett.
14
(
43
),
9683
9689
(
2023
).
21.
L.
Chen
,
Z.
Ma
, and
J. A.
Fournier
, “
Ultrafast transient vibrational action spectroscopy of cryogenically cooled ions
,”
J. Chem. Phys.
159
(
4
),
041101
(
2023
).
22.
S. E.
Sanders
,
M.
Zhang
,
A.
Javed
, and
J. P.
Ogilvie
, “
Expanding the bandwidth of fluorescence-detected two-dimensional electronic spectroscopy using a broadband continuum probe pulse pair
,”
Opt. Express
32
(
6
),
8887
8902
(
2024
).
23.
Q.
Xie
,
Y.
Zhang
,
E.
Janzen
,
J. H.
Edgar
, and
X. G.
Xu
, “
Atomic-force-microscopy-based time-domain two-dimensional infrared nanospectroscopy
,”
Nat. Nanotechnol.
19
,
1108
(
2024
).
24.
P.
Gregoire
,
A.
Kandada
,
E.
Vella
,
R.
Leonelli
, and
C.
Silva
, “
Incoherent population mixing contributions to phase-modulation two-dimensional coherent excitation spectra
,” arXiv:1707.02673 (
2017
).
25.
I.
Bargigia
,
E.
Gutierrez-Meza
,
D. A.
Valverde-Chavez
,
S. R.
Marques
,
A. R.
Srimath Kandada
, and
C.
Silva
, “
Identifying incoherent mixing effects in the coherent two-dimensional photocurrent excitation spectra of semiconductors
,”
J. Chem. Phys.
157
(
20
),
204202
(
2022
).
26.
M.
Bruschi
,
L.
Bolzonello
,
F.
Gallina
, and
B.
Fresch
, “
Unifying nonlinear response and incoherent mixing in action-2D electronic spectroscopy
,”
J. Phys. Chem. Lett.
14
(
30
),
6872
6879
(
2023
).
27.
L.
Bolzonello
,
M.
Bruschi
,
B.
Fresch
, and
N. F.
van Hulst
, “
Nonlinear optical spectroscopy of molecular assemblies: What is gained and lost in action detection?
,”
J. Phys. Chem. Lett.
14
(
50
),
11438
11446
(
2023
).
28.
M.
Bruschi
,
F.
Gallina
, and
B.
Fresch
, “
Simulating action-2D electronic spectroscopy of quantum dots: Insights on the exciton and biexciton interplay from detection-mode and time-gating
,”
Phys. Chem. Chem. Phys.
24
(
45
),
27645
27659
(
2022
).
29.
V.
Coropceanu
,
X.-K.
Chen
,
T.
Wang
,
Z.
Zheng
, and
J.-L.
Brédas
, “
Charge-transfer electronic states in organic solar cells
,”
Nat. Rev. Mater.
4
(
11
),
689
707
(
2019
).
30.
K. J.
Karki
,
J.
Chen
,
A.
Sakurai
,
Q.
Shi
,
A. T.
Gardiner
,
O.
Kuhn
,
R. J.
Cogdell
, and
T.
Pullerits
, “
Before Forster. Initial excitation in photosynthetic light harvesting
,”
Chem. Sci.
10
(
34
),
7923
7928
(
2019
).
31.
D. A.
Blank
,
L. J.
Kaufman
, and
G. R.
Fleming
, “
Fifth-order two-dimensional Raman spectra of CS2 are dominated by third-order cascades
,”
J. Chem. Phys.
111
(
7
),
3105
3114
(
1999
).
32.
K. J.
Kubarych
,
C. J.
Milne
, and
R. J. D.
Miller
, “
Heterodyne detected fifth-order Raman response of liquid CS2: ‘Dutch cross’ polarization
,”
Chem. Phys. Lett.
369
(
5–6
),
635
642
(
2003
).
33.
Z.
Zhang
,
K.
Bennett
,
V.
Chernyak
, and
S.
Mukamel
, “
Utilizing microcavities to suppress third-order cascades in fifth-order Raman spectra
,”
J. Phys. Chem. Lett.
8
(
14
),
3387
3391
(
2017
).
34.
A.
Javed
,
J.
Luttig
,
K.
Charvatova
,
S. E.
Sanders
,
R.
Willow
,
M.
Zhang
,
A. T.
Gardiner
,
P.
Maly
, and
J. P.
Ogilvie
, “
Photosynthetic energy transfer: Missing in action (detected spectroscopy)?
,” arXiv:2406.06784 (
2024
).
35.
M. T.
Zanni
,
N.
Ge
,
Y.
Kim
, and
R. M.
Hochstrasser
, “
Two-dimensional IR spectroscopy can be designed to eliminate the diagonal peaks and expose only the crosspeaks needed for structure determination
,”
Proc. Natl. Acad. Sci. U. S. A.
98
(
20
),
11265
11270
(
2001
).
36.
R. M.
Hochstrasser
, “
Two-dimensional IR-spectroscopy: Polarization anisotropy effects
,”
Chem. Phys.
266
,
273
284
(
2001
).
37.
A.
Tokmakoff
, “
Orientational correlation functions and polarization selectivity for nonlinear spectroscopy of isotropic media. I. Third order
,”
J. Chem. Phys.
105
(
1
),
1
12
(
1996
).
38.
K. M.
Farrell
,
N.
Yang
, and
M. T.
Zanni
, “
A polarization scheme that resolves cross-peaks with transient absorption and eliminates diagonal peaks in 2D spectroscopy
,”
Proc. Natl. Acad. Sci. U. S. A.
119
(
6
),
e2117398119
(
2022
).
39.
K. M.
Farrell
,
C. R.
Fields
,
S. S.
Dicke
, and
M. T.
Zanni
, “
Simultaneously measured kinetics of two amyloid polymorphs using cross peak specific 2D IR spectroscopy
,”
J. Phys. Chem. Lett.
14
(
51
),
11750
11757
(
2023
).
40.
J. D.
Gaynor
,
R. B.
Weakly
, and
M.
Khalil
, “
Multimode two-dimensional vibronic spectroscopy. I. Orientational response and polarization-selectivity
,”
J. Chem. Phys.
154
(
18
),
184201
(
2021
).
41.
G. S.
Schlau-Cohen
,
A.
Ishizaki
,
T. R.
Calhoun
,
N. S.
Ginsberg
,
M.
Ballottari
,
R.
Bassi
, and
G. R.
Fleming
, “
Elucidation of the timescales and origins of quantum electronic coherence in LHCII
,”
Nat. Chem.
4
(
5
),
389
395
(
2012
).
42.
D.
Brida
,
C.
Manzoni
, and
G.
Cerullo
, “
Phase-locked pulses for twoki-dimensional spectroscopy by a birefringent delay line
,”
Opt. Lett.
37
(
15
),
3027
(
2012
).
43.
M. A.
Dugan
,
J. X.
Tull
, and
W. S.
Warren
, “
High-resolution acousto-optic shaping of unamplified and amplified femtosecond laser pulses
,”
J. Opt. Soc. Am. B
14
(
9
),
2348
2358
(
1996
).
44.
E.
Grumstrup
,
S. H.
Shim
,
M.
Montgomery
,
N. H.
Damrauer
, and
M. T.
Zanni
, “
Facile collection of two-dimensional electronic spectra using femtosecond pulse-shaping technology
,”
Opt. Express
15
(
25
),
16681
16689
(
2007
).
45.
N. M.
Kearns
,
R. D.
Mehlenbacher
,
A. C.
Jones
, and
M. T.
Zanni
, “
Broadband 2D electronic spectrometer using white light and pulse shaping: Noise and signal evaluation at 1 and 100 kHz
,”
Opt. Express
25
(
7
),
7869
7883
(
2017
).
46.
P.
Tian
,
D.
Keusters
,
Y.
Suzaki
, and
W.
Warren
, “
Femtosecond phase-coherent two-dimensional spectroscopy
,”
Science
300
(
5625
),
1553
1555
(
2003
).
47.
Z. M.
Faitz
,
D.
Im
, and
M. T.
Zanni
, “
Femtosecond pulse shaper built into a prism compressor
,”
Opt. Express
32
(
4
),
6092
6103
(
2024
).
48.
A. C.
Jones
,
M. B.
Kunz
,
I.
Tigges-Green
, and
M. T.
Zanni
, “
Dual spectral phase and diffraction angle compensation of a broadband AOM 4-f pulse-shaper for ultrafast spectroscopy
,”
Opt. Express
27
(
26
),
37236
37247
(
2019
).
49.
S. H.
Shim
and
M. T.
Zanni
, “
How to turn your pump–probe instrument into a multidimensional spectrometer: 2D IR and vis spectroscopies via pulse shaping
,”
Phys. Chem. Chem. Phys.
11
(
5
),
748
761
(
2009
).
50.
M.
Son
,
Z. T.
Armstrong
,
R. T.
Allen
,
A.
Dhavamani
,
M. S.
Arnold
, and
M. T.
Zanni
, “
Energy cascades in donor-acceptor exciton-polaritons observed by ultrafast two-dimensional white-light spectroscopy
,”
Nat. Commun.
13
(
1
),
7305
(
2022
).
51.
R. D.
Mehlenbacher
,
M. Y.
Wu
,
M.
Grechko
,
J. E.
Laaser
,
M. S.
Arnold
, and
M. T.
Zanni
, “
Photoexcitation dynamics of coupled semiconducting carbon nanotube thin films
,”
Nano Lett.
13
(
4
),
1495
1501
(
2013
).
52.
D.
Abramavicius
and
S.
Mukamel
, “
Coherent third-order spectroscopic probes of molecular chirality
,”
J. Chem. Phys.
122
(
13
),
134305
(
2005
).
53.
A. F.
Fidler
,
V. P.
Singh
,
P. D.
Long
,
P. D.
Dahlberg
, and
G. S.
Engel
, “
Dynamic localization of electronic excitation in photosynthetic complexes revealed with chiral two-dimensional spectroscopy
,”
Nat. Commun.
5
,
3286
(
2014
).
54.
D. B.
Strasfeld
,
C. T.
Middleton
, and
M. T.
Zanni
, “
Mode selectivity with polarization shaping in the mid-IR
,”
New J. Phys.
11
,
105046
(
2009
).
55.
J. E.
Laaser
and
M. T.
Zanni
, “
Extracting structural information from the polarization dependence of one- and two-dimensional sum frequency generation spectra
,”
J. Phys. Chem. A
117
(
29
),
5875
5890
(
2013
).
56.
A. S.
Thomas
,
V. N.
Bhat
, and
V.
Tiwari
, “
Rapid scan white light two-dimensional electronic spectroscopy with 100 kHz shot-to-shot detection
,”
J. Chem. Phys.
159
(
24
),
244202
(
2023
).
57.
J.
Rehault
,
M.
Maiuri
,
A.
Oriana
, and
G.
Cerullo
, “
Two-dimensional electronic spectroscopy with birefringent wedges
,”
Rev. Sci. Instrum.
85
(
12
),
123107
(
2014
).
58.
J.
Nite
,
J.
Cyran
, and
A.
Krummel
, “
Active Bragg angle compensation for shaping ultrafast mid-infrared pulses
,”
Opt. Express
20
(
21
),
23912
23920
(
2012
).
59.
S. H.
Shim
,
D.
Strasfeld
, and
M. T.
Zanni
, “
Generation and characterization of phase and amplitude shaped femtosecond mid-IR pulses
,”
Opt. Express
14
(
26
),
13120
13130
(
2006
).
60.
K. J.
Karki
,
J. R.
Widom
,
J.
Seibt
,
I.
Moody
,
M. C.
Lonergan
,
T.
Pullerits
, and
A. H.
Marcus
, “
Coherent two-dimensional photocurrent spectroscopy in a PbS quantum dot photocell
,”
Nat. Commun.
5
,
5869
(
2014
).
61.
D. J.
Bindl
and
M. S.
Arnold
, “
Efficient exciton relaxation and charge generation in nearly monochiral (7,5) carbon nanotube/C60 thin-film photovoltaics
,”
J. Phys. Chem. C
117
(
5
),
2390
2395
(
2013
).
62.
R. D.
Mehlenbacher
,
T. J.
McDonough
,
M.
Grechko
,
M. Y.
Wu
,
M. S.
Arnold
, and
M. T.
Zanni
, “
Energy transfer pathways in semiconducting carbon nanotubes revealed using two-dimensional white-light spectroscopy
,”
Nat. Commun.
6
,
6732
(
2015
).
63.
M. F.
Garcia-Parajo
,
G. M. J.
Serger-Nolten
,
J.
Veerman
,
J.
Greve
, and
N. F.
Van Hulst
, “
Real-time light-driven dynamics of the fluorescence emission in single green fluorescent protein molecules
,”
Proc. Natl. Acad. Sci. U. S. A.
97
(
13
),
7237
7242
(
2000
).
64.
S. H.
Shim
,
D.
Strasfeld
,
E.
Fulmer
, and
M. T.
Zanni
, “
Femtosecond pulse shaping directly in the mid-IR using acousto-optic modulation
,”
Opt. Lett.
31
(
6
),
838
840
(
2006
).
65.
C.
Middleton
,
D.
Strasfeld
, and
M. T.
Zanni
, “
Polarization shaping in the mid-IR and polarization-based balanced heterodyne detection with application to 2D IR spectroscopy
,”
Opt. Express
17
(
17
),
14526
14533
(
2009
).
66.
O.
Masihzadeh
,
P.
Schlup
, and
R. A.
Bartels
, “
Complete polarization state control of ultrafast laser pulses with a single linear spatial light modulator
,”
Opt. Express
15
(
26
),
18025
18032
(
2007
).
67.
T.
Brixner
and
G.
Berber
, “
Femtosecond polarization pulse shaping
,”
Opt. Lett.
26
(
8
),
557
559
(
2001
).
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