Figure 1

Schematic drawing of a transient-absorption microscope. A pump laser and a probe laser are collinearly combined. The pump laser intensity is modulated by an acousto-optic modulator at 1.13 MHz. The forward probe beam is detected by a photodiode detector. A lock-in amplifier is used to extract the amplitude and phase of the transient-absorption signal. The rectangular box shows that the in-phase and antiphase modulations of the probe field, relative to the modulation of the pump field, corresponds to a negative and a positive transient absorption, respectively.Reuse & Permissions

Figure 2

(a),(b) In-phase and quadrature-channel image of semiconducting SWNTs, respectively. (c) Phase image of semiconducting SWNTs. (d),(e) In-phase and quadrature-channel image of metallic SWNTs, respectively. (f) Phase image of metallic SWNTs. (g),(h) Raman spectrum of the $G$ band in semiconducting and metallic SWNTs, respectively. The data acquisition positions are indicated by cross in (c) and (f). The images in (a),(b) and (d),(e) were acquired with a speed of $50\mu \mathrm{s}$ per pixel, resulting in 13 s per frame. Scale $\mathrm{\text{bar}}=2\mu \mathrm{m}$ for all images.Reuse & Permissions

Figure 3

(a) Extinction spectrum of the metallic and semiconducting SWNTs. (b),(c) Dependence of the transient-absorption signal on the probe wavelength with the pump field at 707 nm and 885 nm, respectively. The probe wavelength of 885 nm used to acquire the phase image in Fig. 2 is indicated with two dotted lines in (b). (d) Electronic energy density state of $s$-SWNTs and diagram showing stimulated emission from $s$-SWNTs. $c$ and $v$ represent conduction and valence bands, respectively. (e) Broadening of the $E_{11}^M$ transition in $m$-SWNTs due to excitation of free electrons by the pump field. When the probe energy is resonant with $E_{11}^M$, the decrease of the oscillator strength leads to in-phase modulation of the probe. When the probe energy is off resonance with $E_{11}^M$, the increase of the oscillator strength leads to antiphase modulation of the probe.Reuse & Permissions

Figure 4

(a) Schematic drawing of the aligned SWNTs on the quartz substrate and excitation and collection of the light. (b) AFM image of aligned individual SWNTs indicated by (1), (2), and (3). At location (2) there are two individual SWNTs separated by 200 nm. Embedded are the height profiles for each SWNT. (c),(d) Transient-absorption images of the same location where the AFM image is taken, with the pump and probe wavelengths at 707 and 885 nm (c), and of 885 and 707 nm (d), respectively. The transient-absorption signals have a lateral resolution of 440 nm, defined as the full width at half maximum of the intensity profile cross the SWNT. The SWNT at (3) shows slightly wider intensity profile at the bottom than at the upper part (c), possibly due to the presence of another short SWNT at the bottom as shown in the AFM image.Reuse & Permissions