## 3 Results and Discussion
### Results of the Experimental Study and Their Interpretation  
Spectral dependence of the photo-sensor response was recovered using the experimental data obtained in the accordance with the above subsection. The switch-on mode of the device corresponded to that shown in Figure 5, when a single electrode, a gate, was used for controlling. Analysis of the measurement results in Figure 8a, performed at various levels of the gate potential, shows that an increase in the electrostatic field strength leads to a noticeable increase in the photon emission with the wavelength ranging between 520-580 nm. A two-fold increase in the photocurrent is achieved with a slight increase (about 3%) in electrostatic field strength. Regarding the rest of the investigated range of the wavelength of irradiating laser, a growth in the photocurrent is also observed, though it is less evident. It is necessary to notice an increased irregularity of the spectral curves in Figure 8a. The laser with a tunable working wavelength used in the experiment has a spectral dependence of the pulse energy, as shown in Figure 8b, and a gap ranging within 700-800 nm. During the tests in the available range of tuning of the near-infrared radiation (from 800 to 1064 nm), 0.2-0.8 mA photocurrent of the vacuum sensor under laser pulse irradiation of 0.2-0.5 mJ was also detected. Figure 7: Dependence of the electrostatic field strength at the unit potential U\({}_{\mathrm{g}}\) in the vicinity of the tip of the emitter blade (**a**) and along the perimeter of the generatrix 0–5 (**b**); (**c**,**d**), the same in the case when the potentials are applied to both control electrodes of the photosensor U\({}_{\mathrm{g}}\) = 1 V and U\({}_{\mathrm{a}}\) = 4 V.  
In our view, the observed regularities of the far-field diffraction effect of the optical wave at the submicron scale stage (emitter--gate) on significant phase dispersion in the amplitude and direction of the Poiting vector over the molybdenum emitter surface (see simulation results in Figure 5) provide an adequate interpretation of the experimentally observed processes. The position of localization zones of the specific optical signal absorption power, on the one hand, and unchanging position of the electrostatic field localization zone, on the other hand, which rapidly change with the frequency of the irradiating beam, lead to their asynchronous behavior. A lack of coordination of the two types of localization zones (optical absorption and electrostatic external field) relating the mutual position results in the decrease of the photo-sensor response within a relatively narrow frequency range. With a further change in the radiation wavelength, there conditions are favorable for both the absorption and tunneling of hot electrons into the vacuum. Under such conditions, an emerging possibility for an additional adjustment of the system by varying positions of electrostatic field localization zones and changing the potential of control electrodes, as shown in Figure 7, ensures the prospect for improving the vacuum photosensor parameters. The illustrated possibility that ensures the performance of the vacuum photosensor in a wide wavelength range (ranging from the visible up to near infrared radiation) is explained by a single photon effect of the tunnel photoemission process. To prove the performance reliability, we provide the measurements of the photocurrent as the function of the laser pulse energy. Linearity of the dependence designed in Figure 9 indicates the absence of nonlinear processes characteristic of the multiphoton photoemission. This allows us to predict a possibility to further upgrade the efficiency of the tunnel photoemission. Figure 8: Spectral dependence of the sensor response at two levels of the gate potential U\({}_{\text{g}}\)—158 V and 170 V (**a**); laser pulse energy dependence vs. wavelength (**b**).