Photonic-Crystal-Fiber Quantum Probes for High-Resolution Thermal Imaging

Sean M. Blakley, Christapher Vincent, Ilya V. Fedotov, Xinghua Liu, Kyle Sower, Dawson Nodurft, Jiru Liu, Xiaohan Liu, Viatcheslav N. Agafonov, Valery A. Davydov, Alexey V. Akimov, and Aleksei M. Zheltikov

Phys. Rev. Applied 13, 044048 – Published 17 April 2020

Abstract

All-optical thermometry presents a promising avenue of investigation for sensitive biological and electronic systems, with methods free of radio-frequency interference of particular importance. In this work, an all-optical scanning fiber thermometer is tested and shown to possess $5 μ m$ spatial and $20 mK / \sqrt{Hz}$ temperature resolution. This probe is then used to generate noncontact scanning thermal images of active circuit elements with microscale thermal features.

Received 19 November 2019
Revised 14 February 2020
Accepted 2 March 2020

DOI:https://doi.org/10.1103/PhysRevApplied.13.044048

Physics Subject Headings (PhySH)

Medical physics & public health Metrology Nanocrystals Quantum sensing Temperature Vacancies

Diamond

Fluorescence

Atomic, Molecular & Optical

Authors & Affiliations

Sean M. Blakley ^1,*, Christapher Vincent¹, Ilya V. Fedotov^1,2,3,4, Xinghua Liu ¹, Kyle Sower¹, Dawson Nodurft¹, Jiru Liu¹, Xiaohan Liu¹, Viatcheslav N. Agafonov ⁵, Valery A. Davydov⁶, Alexey V. Akimov ^1,2,7, and Aleksei M. Zheltikov^1,2,3,4

¹Department of Physics and Astronomy, Texas A&M University, College Station, Texas 77843-4242, USA
²Russian Quantum Center, Skolkovo, Moscow Region 143025, Russia
³Physics Department, International Laser Center, M. V. Lomonosov Moscow State University, Moscow 119992, Russia
⁴Kazan Quantum Center, A. N. Tupolev Kazan National Research Technical University, Kazan 420126, Russia
⁵GREMAN, UMR CNRS CEA 6157, F. Rabelais University, 37200 Tours, France
⁶L. F. Vereshchagin Institute for High Pressure Physics, Russian Academy of Sciences, Troitsk, Moscow 108840, Russia
⁷P. N. Lebedev Institute RAS, Leninsky Prospect 53, 119991 Moscow, Russia

^*smb784@umd.edu

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Vol. 13, Iss. 4 — April 2020

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Images

Figure 1
The experimental diagram of the $Ge$ - $V$ diamond (dashed green insert) fiber-thermometer probe. (a) The fluorescence spectrum at 50 mW laser power, with a characteristic zero-phonon peak at approximately 601 nm collected by the probe (b), which consists of a $Ge$ - $V$ –microdiamond ensemble affixed to the 50- $μ m$ core (dashed red inset) of a step-index fiber. The probe is immersed in a temperature-controlled water bath for sensitivity and calibration measurements. (c) For scanning-probe measurements, a F-NL-5/1040 photonic crystal fiber with a 5- $μ m$ core (dashed blue inset) is used. An approximately 5- $μ m$ -diameter Ge-V microdiamond is affixed to the 5- $μ m$ fiber core. The probe tip is scanned in 5- $μ m$ steps and temperature measurements are made at each step on the $x$ , $y$ , or $z$ axes in front of various active circuit elements.
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Figure 2
(a) The peak-wavelength (black squares) calibration curve with a $0.0078 nm /^{\circ} C$ response from a linear fit (black dashed trace) and (b) the bandwidth-averaged sensitivity (black circles) and probe thermalization (red circles) for a microdiamond ensemble on a step-index fiber probe [(a), inset], measured at 0.5, 5, 20, and 50 mW laser power ( $P_{λ}$ ). The black dashed and red dotted traces are for visual aid. (c) The SNR (black circles) and probe thermalization (red circles) for a single-diamond PCF probe [(c), inset], measured at $P_{λ} = 0.5$ , 1.5, 3, and 9 mW. The SNR response is shown to be in the linear regime with respect to the power; thus the fluorescent transition is not saturated. The probe thermalization as a function of the power is comparable to that for an index-guided fiber. (d) The temperature noise spectrum ( $T_{noise}$ ) as a function of the noise frequency ( $ν_{noise}$ ). The temperature noise floor is approximately 55 mK at $P_{λ} = 4 mW$ ; a $12^{\circ} C$ thermalization of the PCF probe was measured at $P_{λ} = 9 mW$ in an air environment.
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Figure 3
(a) The $x$ -axis thermal imaging of a crossed pair of wires with diameter $30 μ m$ ( $d_{1}$ ) and $15 μ m$ ( $d_{2}$ ), respectively, supplied with variable current (I). The probe is located in the $y$ - $z$ plane, corresponding to an 800- $μ m$ wire separation and a 10- $μ m$ minimum displacement from the 30- $μ m$ wire. An $x$ -axis scan with a 5- $μ m$ step size generates a thermal image of the wire pair (inset). (b) The $x$ -axis temperature profile of the wire pair (blue, red dashed lines) at multiple different current values.
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Figure 4
(a) The $z$ -axis temperature dependence as a function of the displacement ( $δ z$ ) from $z_{0} = 20 μ m$ , measured by the PCF thermometer probe. Temperature fluctuations on the order of $+ / - 1^{\circ} C$ induced by convection are observed. An optical image of a wire-grid segment [(a), inset]. Fourier-filtered scanning thermal images in the $x$ - $y$ plane taken at $δ z$ values of (b) $0 μ m$ , (c) $20 μ m$ , and (d) $40 μ m$ , respectively, demonstrating heating between 40 and $50^{\circ} C$ [color scale in (a)], and prominent grid features [(b), (c), and (d), insets] possessing a differential temperature ( $δ T$ ) of less than $2^{\circ} C$ [(b), inset color scale]. (e) The $x$ - and $y$ -axis temperature distributions measured along the dashed yellow lines of the inset to (a) (solid and dashed traces) for the inset regions of (b) (red traces), (c) (green traces), and (d) (blue traces), respectively. The dashed (dotted) purple lines indicate the center (edges), respectively, of the wires depicted in the inset to (a). (f) The $y$ -axis temperature distribution (purple trace) at $δ x = 490 μ m$ [black dotted line in (b)]. The average temperature of wires (orange bars) possess visible wire-to-wire variations, indicating a spatially varying current distribution along the $y$ axis.
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