Optical control of resonant light transmission for an atom-cavity system

We demonstrate the manipulation of transmitted light through an optical Fabry-Pérot cavity, built around a spectroscopy cell containing enriched rubidium vapor. Light resonant with the ${}^{87}\mathrm{Rb}{D}_2$ $\left(F=2,F=1\right)$ $\leftrightarrow F^{\prime }$ manifold is controlled by the transverse intersection of the cavity mode by another resonant light beam. The cavity transmission can be suppressed or enhanced depending on the coupling of atomic states due to the intersecting beams. The extreme manifestation of the cavity-mode control is the precipitous destruction (negative logic switching) or buildup (positive logic switching) of the transmitted light intensity on intersection of the transverse control beam with the cavity mode. Both the steady-state and transient responses are experimentally investigated. The mechanism behind the change in cavity transmission is discussed in brief.

Figure 1

Energy-level schematic corresponding to the $D_2$ transitions of ${}^{87}\mathrm{Rb}$. The right pane of the figure shows the reduced four-level scheme relevant to the experiment. The probe and the control laser frequencies ${\omega }_p$ and ${\omega }_c$ are shown. The superscripts $+$ and $-$ refer to the positive and negative logic of switching, respectively.

Figure 2

Schematic of the experimental setup. The FP cavity with the ${}^{87}\mathrm{Rb}$ cell is shown. The probe beam (solid line) is coupled into the cavity and the transmission and reflection ports are monitored using the photodiodes ${\mathrm{PD}}_T$ and ${\mathrm{PD}}_R$, respectively. The spatial profile of the transmitted mode is captured using a CCD camera. The control beam (dashed line) intersects the cavity mode over a small spatial region and is monitored using ${\mathrm{PD}}_C$. Switching and intensity modulation of the two beams are done using the AOMs as shown.

Figure 3

Measured decay and rise of the cavity transmission for the probe, on- and off-resonance. The decay of the steady-state intensity is measured in transmission for (a) the off-resonance case and (b) the on-resonance case. In both cases the fall time has submicrosecond time constants. Also shown is the rise in the transmitted intensity (c) off-resonance and (d) on-resonance. Here the rise time constant for the off-resonance case is submicrosecond, whereas for the on-resonance case it is significantly larger.

Figure 4

Transmitted light through the cavity, at ${\omega }_2$, as a function of input light power for up and down cycles. The arrows shows the directions of the input intensity scan. The cavity transmission with increasing input power is the solid red line, while the solid blue line gives the transmission as a function of falling input power, in the absence of the control beam. When the control beam is tuned to ${\omega }_1$, the hysteresis feature shifts to higher input powers. In the presence of the control light with a power of 10 mW, the new increasing power response is represented by the green circles, while the orange circles give the falling input-power response. The shift in the cavity response, in the presence of the control light, results in the control of the intracavity light intensity.

Figure 5

Cavity transmission of probe light over a free spectral range, as a function of the cavity length (in frequency units), illustrated by the thin gray trace. When the control light intersects the cavity mode, we see the complete suppression of the cavity transmission peaks shown as the thick black trace. The transmission has been extinguished and has not been shifted in frequency.

Figure 6

Time trace recording three cycles of switching. The upper trace shows the temporal profile of the control laser and the bottom trace shows the temporal profile of the cavity transmission. The transmission is high when $I_c=0$ and low when $I_c>I_{c;s}$. For this set of probe and control frequencies, the switch operates in negative logic.

Figure 7

Change in the efficiency of the switching as a function control laser power. The $h_{\text{off}}$ value is baseline corrected for determining the efficiency.

Figure 8

Change in the efficiency of attenuation as a function of the control laser frequency across the Doppler absorption profile of the control laser.

Figure 9

(a) and (b) Image of the intersection region of the cavity mode with the control beam (200 pixels $\approx$ 25 mm). The bold two-headed arrow marks the direction of the cavity mode and the dashed single-headed arrow the control beam. The system is in the partial attenuation regime for this experiment. Illustrated are (a) increased light scattering accompanying probe attenuation, i.e., the two beams on complementary transitions, and (b) decreased light scattering accompanying probe enhancement, i.e., the two beams on the same transition. Also illustrated is (c) the fluorescence intensity in arbitrary units along the cavity mode, from which it is clear that the scattering from the intersection volume is enhanced for the negative-logic configuration (blue thin line) and reduced for the positive-logic case (red thick line).

Figure 10

Sweep across the cavity resonance in the presence of the control beam. The orange (dotted) and red (thick line) traces are cavity reflection $\left({\mathrm{PD}}_R\right)$ and transmission $\left({\mathrm{PD}}_T\right)$ signals, respectively. The blue trace (solid line) is the transmitted intensity $\left({\mathrm{PD}}_C\right)$ of the control beam. In the absence of the control light, the ${\mathrm{PD}}_R$ dip is deeper and the ${\mathrm{PD}}_T$ peak is higher. When the control light is turned on, at the cavity resonance, the peak in ${\mathrm{PD}}_T$ goes down $(\downarrow )$, the dip in ${\mathrm{PD}}_R$ decreases $(\uparrow )$, and the transmitted control light goes down $(\downarrow )$. The multiplicative factors indicate the relative signal strengths.

Figure 11

Transient response of the cavity output probe light for the negative-logic switching. The rise and fall times are measured to be $\approx 1$ ms for 10% to 90% switching.

Figure 12

Illustration of the cavity-mode enhancement. The polarization direction of the control light is parallel to the cavity axis. The red thick line is the cavity transmission and the blue thin line is the intensity of the control light $(30\times$ magnification), analyzed using a Wollaston prism. The increase in the intensity of the transmitted light for both the probe and control beams in the incident polarization state, when the cavity supports intensity buildup, results in a suppression of fluorescence in the intersection volume, as shown in Figs. 9 and 9. The cavity-mode enhancement is independent of the control light polarization state.

Figure 13

Transient (a) rise and (b) fall response of the cavity output probe light for positive logic switching. Time scales of the fast and slow responses obtained from double-exponential fits to the data are provided in Table 3 and match closely the negative-logic case.