Generalized lock-in amplifier for precision measurement of high frequency signals

Fu, Siyuan; Sakurai, Atsunori; Liu, Liang; Edman, Fredrik; Pullerits, Tõnu; Öwall, Viktor; Karki, Khadga Jung

doi:10.1063/1.4827085

Cited by 29 publications

(25 citation statements)

References 13 publications

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“…The signal and the reference are digitized simultaneously at the rate of 10 MSa/s (mega samples per second). The phases and amplitudes of the signals modulated at the frequencies ϕ 4 − ϕ 3 − ϕ 2 + ϕ 1 and ϕ 4 − ϕ 3 + ϕ 2 − ϕ 1 are extracted from the digitized data by using the algorithms of the generalized lock-in amplifier (GLIA) [52][53][54] . The measurements are done in time domain by varying the time delays.…”

Section: Methodsmentioning

confidence: 99%

Vibronic coherence contributes to photocurrent generation in organic semiconductor heterojunction diodes

Bian

Chen

et al. 2020

Nat Commun

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Charge separation dynamics after the absorption of a photon is a fundamental process relevant both for photosynthetic reaction centers and artificial solar conversion devices. It has been proposed that quantum coherence plays a role in the formation of charge carriers in organic photovoltaics, but experimental proofs have been lacking. Here we report experimental evidence of coherence in the charge separation process in organic donor/acceptor heterojunctions, in the form of low frequency oscillatory signature in the kinetics of the transient absorption and nonlinear two-dimensional photocurrent spectroscopy. The coherence plays a decisive role in the initial~200 femtoseconds as we observe distinct experimental signatures of coherent photocurrent generation. This coherent process breaks the energy barrier limitation for charge formation, thus competing with excitation energy transfer. The physics may inspire the design of new photovoltaic materials with high device performance, which explore the quantum effects in the next-generation optoelectronic applications.

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Section: Methodsmentioning

confidence: 99%

Vibronic coherence contributes to photocurrent generation in organic semiconductor heterojunction diodes

Bian

Chen

et al. 2020

Nat Commun

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“…32 The second output of the Mach-Zehnder interferometer was directed to a SC generation kit (SCKB, Thorlabs). The white-light from 9 the SC generation kit was detected by an amplied photodiode (PD36A, Thorlabs).…”

Section: Resultsmentioning

confidence: 99%

Evidence of High-Order Nonlinearities in Supercontinuum White-Light Generation from a Gold Nanofilm

et al. 2018

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White-light supercontinuum generation can be readily observed when gold nanostructures are irradiated with short pulses of light. It is believed that the nanostructures enhance the optical elds, which facilitates the supercontinuum white-light generation from the surrounding environment or the substrate. Here, we investigate the dierent nonlinear processes that contribute to the generation of the supercontinuum from plasmonic nanostructures themselves using a technique that isolates the dierent nonlinear contributions. By exciting a gold nanolm with a pair of frequency shifted optical frequency combs, we demonstrate multiple modulation frequencies in the supercontinuum. and supercontinuum (SC) generation 5,10 can be observed at higher intensities. SC generation is also routinely observed when intense pulsed lasers are focused onto any dielectric medium, 11 and it has been suggested that the SC from the gold nanostructures originates due to the emission from the surrounding dielectric medium. The spectral broadening leading to the SC generated from the dielectrics is mainly due to the third-order nonlinear processes such as self-phase modulation (SPM), cross-phase modulation (XPM) and four-wave mixing (FWM). In such a process, the spectral width of the broaden spectrum, ∆ω, is proportional to the product of the intensity and the interaction length, ∆ω ∝ Iz (here I is the intensity and z is the interaction length). 11 In a typical dielectric medium, an excitation intensity of 10 13 10 14 W/cm 2 and the interaction length of few millimeters are necessary to observe appreciable spectral broadening. Alternatively, one can substantially increase the interaction length by using guided propagation of pulses in nonlinear optical (NLO) bers in order to generate broad spectrum at lower excitation intensity. 1214 The SC from gold nanostructures, on the other hand, is observed at a relatively lower excitation intensity (∼ 10 10 − 10 11 W/cm 2 ) as well as very short interaction length (∼ few tens of nanometers). 10 Although gold 2 nanostructures can locally enhance the electric eld, the intensity that is required to generate the SC within the interaction length of few nanometers from the surrounding substrate by SPM, XPM and FWM is about 10 18 W/cm 2 . As metal nanostructures cannot withstand such high intensities, it is unlikely that SC from the gold nanostructures and the dielectric medium originate from the same nonlinear processes.The SC generation has not been observed from the bulk gold despite its high intrinsic nonlinearity. 15 Thus it is reasonable that the optical properties of gold that only manifest in the nanostructures contribute to the nonlinear process. The nonlocal response of free electrons to the incident light elds in metals is one of such properties. 16 Generally, lightmatter interactions in dielectric materials are described by the local-response approximation (LRA) in which the electric displacement eld D(r, ω) induced at a point r by an incident light eld of frequency ω is proportional to the...

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“…The signal from the APD and the PD are digitized simultaneously at the rate of 10 MSa/s (mega samples per second). The phase and the amplitude of the signal from the APD (two-photon PL) is analyzed with respect to the signal from the PD (reference) by using the algorithms of the generalized lock-in amplifier (GLIA) [43][44][45]. The two-photon excitation spectra are recorded as a function of the time delay between the two beams.…”

Section: Methodsmentioning

confidence: 99%

Two-photon excitation spectroscopy of 1,5–Diphenyl-1,3,5-hexatriene using phase modulation

Kumar

Karki

2019

J. Phys. Commun.

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We have used two-photon Fourier transform spectroscopy to investigate the first singlet excited state (S 1 ) of a prototypical polyene molecule 1,5-Diphenyl-1,3,5-hexatriene. As the S 1 state in the polyenes is a one-photon forbidden transition, the structure of its vibrational levels cannot be studied using resonant linear excitation. Although this level is accessible with two-photon excitation, previous studies done by using wavelength tunable pulsed lasers did not have enough resolution to investigate the details of the vibrational levels. In Fourier transform spectroscopy, one uses a pair of laser beams to excite the sample. The measurements are done by varying the time delay between the pulses. The spectral resolution is given by the inverse of the maximum time delay rather than the spectral width of the pulses. We have used the method to investigate the vibrational levels of the S 1 state. In our implementation, we have used phase modulation to carry out the measurements in the rotating frame, which requires less data points along the time delay thereby significantly reducing the measurement time.

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Generalized lock-in amplifier for precision measurement of high frequency signals

Cited by 29 publications

References 13 publications

Vibronic coherence contributes to photocurrent generation in organic semiconductor heterojunction diodes

Vibronic coherence contributes to photocurrent generation in organic semiconductor heterojunction diodes

Evidence of High-Order Nonlinearities in Supercontinuum White-Light Generation from a Gold Nanofilm

Two-photon excitation spectroscopy of 1,5–Diphenyl-1,3,5-hexatriene using phase modulation

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