DOI: 10.5061/dryad.k3j9kd5kt
title: Spatial-offset pump-probe imaging of nonradiative dynamics at optical resolution

description: Nonradiative photothermal (PT) and photoacoustic (PA) processes have found
 widespread applications in imaging, stimulation, and therapy. Mapping the
 generation and propagation of PA and PT waves with resolution is important
 to elucidate how these fields interact with biological systems. To this
 end, we introduce spatial offset pump-probe imaging (SOPPI). By spatially
 offsetting the pump beam and the probe beam, SOPPI can image
 simultaneously PA and PT wave propagation with nanosecond temporal
 resolution, micrometer spatial resolution, 65 MHz detection bandwidth, and
 a sensitivity of 9.9 Pa noise equivalent pressure. We first map the PA and
 PT evolution from a fiber emitter, and how the wave interacts with a mouse
 skull and brain slices. SOPPI imaging of PA waves from a tapered fiber
 with water as an absorber shows a wavelength-dependent generation, an
 evanescent wave-generated PA, and a back-propagated acoustic Mach Cone. At
 last, a SOPPI-PACT is developed to reconstruct the pigment distribution
 inside a zebrafish larva with high precision and signal-to-noise ratio.
description: # Spatial-offset pump-probe imaging of nonradiative dynamics at optical
 resolution Dataset DOI: [10.5061/dryad.k3j9kd5kt](10.5061/dryad.k3j9kd5kt)
 ## Description of the data and file structure The data presented here is
 for the manuscript titled "**Spatial offset pump-probe imaging of
 nonradiative dynamics at optical resolution**". Data for each figure
 are organized separately, from Figure1 to Figure5 and SI. **Figure 1.
 Using a pump probe method to measure the photoacoustic and photothermal
 field generated by a fiber.** * (**B**). Representative AC signal detected
 by the pump probe imaging system. *Variable definitions:                  
   PA: Photoacoustic.                     PT: Photothermal.                
     Time: Recording time. Unit: Microsecond.                     AC
 Intensity: The signal recorded in the AC channel to plot the PA and PT
 traces. * (**C**). Decomposition of the raw signal. *Variable definitions:
            Time: Recording time. Unit: Microsecond.            PA:
 Photoacoustic signal decomposed.            PT: Photothermal signal
 decomposed. * (**D**). Spatial resolution characterization of SOPPI using
 a 3 μm PMMA bead.           *Variable definitions:                    
  PSF: Point Spread Function. * (**E**). PA signal generated by FE and
 measured by hydrophone (orange) and SOPPI (yellow).  *Variable
 definitions: File: Hydrophone_PA_time trace / Hydrophone_PA_frequency
 spectrum.             Frequency: Ultrasound frequency. Unit: Hz.          
   Magnitude: Magnitude of the frequency components at different
 frequencies. (arbitrary unit)             Time: Recording time. Unit:
 Nanosecond.             Amplitude: Amplitude of the PA signal detected by
 the hydrophone. (arbitrary unit) File: SOPPI_PA_time trace /
 SOPPI_PA_frequency spectrum.             Frequency: Ultrasound frequency.
 Unit: Hz.             Magnitude: Magnitude of the frequency components at
 different frequencies: arbitrary unit             Time: Recording time.
 Unit: Nanosecond.             Amplitude: Amplitude of the PA signal
 detected by the SOPPI: arbitrary unit * (**F**). Peak to peak pressure
 measured by hydrophone and SOPPI plotted as a function of pump energy.
 *Variable definitions:             Pump energy: The pulse energy of the
 pump laser. Unit: microjoule.             SOPPI: Signal amplitude detected
 by the SOPPI.             Hydrophone: Signal amplitude detected by the
 hydrophone. **Figure 2. SOPPI reveals the spatial evolution of PA and PT
 signal generated by a fiber emitter.** * (**A**). An overlaid image of PA
 (green) and PT (red) signals at every 100 ns from 0 ns to 1400 ns.
 *Variable definitions:              t0 ~ t1400: Image at time = 0 ns ~
 1400 ns.              Overlap: The overlap imaging from t0 to t1400.  *
 (**B**). High-frequency component of the PA signal from panel A. Bottom:
 PA signal amplitude plotted as a function of location. * (**C**) Time
 trace and Fast Fourier transfer of the high-frequency component of the
 photoacoustic signal. *Variable definitions:           File:
 High_frequency_PA frequency spectrum                        Frequency:
 Ultrasound frequency. Unit: Hz.                        Magnitude:
 Magnitude of the frequency components at different frequencies. (arbitrary
 unit)           File: High_frequency_PA time trace                      
  Time: Recording time. Unit: Nanosecond.                        Amplitude:
 Amplitude of the PA signal detected by the SOPPI: arbitrary unit * (**D**)
 Spatial distribution of high-frequency PA (orange) and low-frequency PA
 (blue).  *Variable definitions: File: High frequency profile            
  x position: distance away from the fiber emitter. Unit: Micrometer.      
        Intensity: Field intensity: arbitrary unit File: Low frequency
 profile              x position: distance away from the fiber emitter.
 Unit: Micrometer.              Intensity: Field intensity: arbitrary unit
 * (**E**) Low-frequency component of the PA signal from panel A. Bottom:
 PA signal amplitude plotted as a function of location * (**F**) Time trace
 and Fast Fourier transfer of the low-frequency component of the
 photoacoustic signal. *Variable definitions:           File:
 Low_frequency_PA frequency spectrum                        Frequency:
 Ultrasound frequency. Unit: Hz.                        Magnitude:
 Magnitude of the frequency components at different frequencies: arbitrary
 unit           File: Low_frequency_PA time trace                      
  Time: Recording time. Unit: Nanosecond.                        Amplitude:
 Amplitude of the PA signal detected by the SOPPI: arbitrary unit * (**G**)
 Spatial distribution of the normalized photothermal signal generated by a
 fiber emitter. * (**H**) Representative time trace of the photothermal
 signal inside and outside the FE. *Variable definitions:            
  Time: Recording time. Unit: Microsecond.              Inside:
 Photothermal trace inside the fiber.              Outside: Photothermal
 trace outside the fiber. * (**I**) PT intensity plotted as a function of
 distance away from the FE. *Variable definitions:               Distance:
 Relative distance from inside to the outside of the fiber. Unit:
 Micrometer.               Intensity: Relative temperature increase.
 (arbitrary unit) **Figure 3. SOPPI of PA/PT fields generated by water
 through a tapered optical fiber.** * (**C**) PA signals generated from
 water at different wavelength of pump laser at a location 160 μm away from
 the tip. *Variable definitions:              Time: Recording time. Unit:
 Nanosecond.              PA_1448: PA signal when pump wavelength is 1448
 nm. Unit: a.u.              PA_1928: PA signal when pump wavelength is
 1928 nm. Unit: a.u. * (**D-E**) PA amplitude and frequency spectrum under
 different wavelength of pump laser in NIR. *Variable definitions:        
   File: water_PA and absorption                        wavelength: Pump
 laser wavelength. Unit: nanometer.                        absorption:
 water absorption spectrum: arbitrary unit                        PA: water
 generated PA intensity: arbitrary unit           File: water_PA spectrum  
                      wavelength: Pump laser wavelength. Unit: nanometer.  
                      Frequency: Ultrasound frequency. Unit: MHz. *
 (**F-J**) Spatial distribution of PA (green and yellow) and PT fields
 (red) at 0-200 ns after the laser was turned on. Dashed boxes: evanescent
 wave absorption (blue), Mach cone (orange), and tip of the tapered fiber
 (green) * (**K**) three PA waves from evanescent wave absorption (blue),
 Mach cone (orange), and tip of the tapered fiber (green) at 1920 nm pump.
 The signal was measured at the “probe” point labeled as purple. *Variable
 definitions:                Time: Recording time. Unit: Nanosecond.      
          Amplitude: Amplitude of the PA signal generated. arbitrary unit
 **Figure 4. SOPPI of ultrasound penetrating through mouse brain tissue and
 skull.** * (**A**) transmission DC image of the fiber emitter and a brain
 slice with 500 μm thickness. Scale bar: 100 μm. * (**B**) Spatial
 distribution of FE-generated PA field in brain slice. * (**C**) Spatial
 distribution of PA signal after normalization with respect to DC signals.
 * (**D**) Representative time trace of the incident / transmitted PA
 signal. *Variable definitions:                Time: Recording time. Unit:
 Nanosecond.                Incident US: Amplitude of the incident PA
 signal generated: arbitrary unit                Transmitted US: Amplitude
 of the transmitted PA signal generated: arbitrary unit * (**E**) PA signal
 intensity before/after penetrating the brain slice. *Variable definitions:
               Location: Relative location from inside to the outside of
 the brain slice. Unit: Micrometer.               After correction: PA
 intensity after correction: arbitrary unit               Before
 correction: PA intensity before correction: arbitrary unit * (**F**)
 transmission DC image of the fiber emitter and a piece of mouse skull. *
 (**G**) Spatial distribution of the PA field across the skull. * (**H**)
 Nine representative frames of photoacoustic wave penetrating the skull.
 US: ultrasound. **Figure 5. Photoacoustic computed tomography of a
 zebrafish using SOPPI.** * (**A**) Schematic of a PACT imaging of a
 zebrafish using SOPPI. The probe beam was scanned around the zebrafish
 following the yellow dashed line. * (**B**) Representative PA signal
 generated by pigments inside the zebrafish and detected by SOPPI.
 *Variable definitions:           File: Zebrafish_PA_frequecy spectrum    
                    Frequency: Ultrasound frequency. Unit: Hz.            
            Magnitude: Magnitude of the frequency components at different
 frequencies: arbitrary unit           File: Zebrafish_PA_time trace      
                  Time: Recording time. Unit: Nanosecond.                  
      Amplitude: Amplitude of the PA signal generated by pigments in the
 zebrafish larva: arbitrary unit * (**C**) Transmission imaging of a
 zebrafish. * (**D**) Reconstructed mapping of pigments inside the
 zebrafish using SOPPI-PACT. * (**E**) Overlap of transmission and PACT
 results. * (**F**) Comparison of SOPPI-PACT and classic PACT results. *
 (**G**) Comparison of XSSIM and XPSNR between SOPPI-PACT and classic PACT.
 *Variable definitions:              SOPPI: XPSNR or XSSIM of SOPPI-PACT
 result.              classic: XPSNR or XSSIM of classic-PACT result.
 **Supplementary Information** * **Figure S1. Sensitivity characterization
 of SOPPI.** a. SOPPI shows a noise equivalent pressure of 9.89 Pa. b. PA
 signal from 1.25 mg/ml Hemoglobin in water. *Variable definitions: File:
 Figure S1a                 Time: Recording time. Unit: Nanosecond.        
         PA: Amplitude of the PA signal generated by a fiber emitter:
 arbitrary unit File: Figure S1b                 Time: Recording time.
 Unit: Nanosecond.                 PA: Amplitude of the PA signal generated
 by 1.25 mg/ml Hemoglobin in water: arbitrary unit * **Figure S2. SOPPI
 visualizing near-field acousto-thermal process.** a. Four representative
 frames of PA and PT field distribution. b. signal detected at the boundary
 of the fiber emitter. **c.** signal detected inside the fiber emitter.
 *Variable definitions: File: Figure S2b                 Time: Recording
 time. Unit: Nanosecond.                 PA: Amplitude of the PA signal
 generated at position 1: arbitrary unit File: Figure S2c                
 Time: Recording time. Unit: Nanosecond.                 PA: Amplitude of
 the PA signal generated at position 2: arbitrary unit * **Figure S5.
 Background and noise level of SOPPI PACT.** *Variable definitions:        
      Distance: Relative location in the PACT reconstruction image. Unit:
 Micrometer.              Intensity: Field intensity: arbitrary unit
 **DAQ_Square_Fish_Weight** * This is the MATLAB script used to reconstruct
 the pigment distribution inside the zebrafish using a weighted
 delay-and-sum algorithm. Details of the algorithm can be found in the
 Supplementary Information: Weighted-Delay-and-Sum (W-DAS) SOPPI-PACT
 reconstruction algorithm.