Fig shows schematically a simultaneous fabrication of cells

Fig. 3 shows schematically a simultaneous fabrication of 97 cells. At the first stage (I) of the technological process, cavities were etched by a deep alkaline etching through the entire thickness of the KEF-20 silicon wafer with the (100) orientation. The etching was carried out in a 30% aqueous solution of potassium hydroxide during 8 h at 80 °C. At the second stage (II), a flat glass plate (LK5 glass) was attached to the bottom side of the silicon wafer by using anodic bonding in air at 450 °C under a voltage of 800 V for 30 min. At the third stage (III), a titanium mini-tablet containing a few percent of rubidium dichromate about 200 µm in diameter was placed into each of the 97 cells by using a special mask. At the fourth stage (IV), the second glass plate was attached to the upper side of the silicon wafer by anodic bonding. Bonding was performed in a neon LY335979 cost (under a pressure of 200 mmHg) during 2 h at 400 °C, under a voltage of 350 V. Prior to bonding, all elements were outgassed under vacuum (under pressure of 10−4 mmHg) at 450 °C for an hour. At the fifth stage (V), the three-layer structure (glass–silicon–glass) was separated into chips by a diamond cutting disk. At the sixth stage (VI), each tablet was activated by an IR laser.
Investigation of cell characteristics To study experimentally the small-size cells prepared by the procedure described above, the setup presented schematically in Fig. 4 was used. A laser beam (L) was fed to an electrooptical phase modulator (EOM) modulated by a sinewave signal from a microwave generator (MWFG). At the EOM output, the first order spectral −1 and +1 components separated by twice the frequency of the modulating microwave signal appeared. The carrier component “0” was suppressed by 70% as compared with its intensity at the EOM input. Then the light passed through a collimator (CL) and polaroids P (λ/2 and λ/4), was partially absorbed in the cell (Rb Cell) and was detected by a photoreceiver (PhR). After that the signal amplified by an amplifier (A) was fed to the oscilloscope (OSc) input. The cell temperature was stabilized by a thermostat (T) that included a heating element (Ht) and a thermistor (Rt) that provided measurements of the cell temperature. The thermostat was controlled by a control unit (TCU). A magnetic shield (MS) screened the cell from external magnetic fields, the internal magnetic field B0 was produced by a built-in coil. A low-frequency modulation generator (LFMG) provided the modulation of the resonance conditions for observation of CPT signals. A laser control unit (LCU) was used to stabilize laser current and temperature and to weakly modulate the laser current in order to observe the absorption spectra of 87Rb atoms. In the experiment, the radiation absorption signal was detected by scanning its frequency in the region of the D2 line of absorption of 87Rb atoms. The absorption cavity was placed in the optical path according to the scheme shown in Fig. 2a (microwave EOM modulation was turned off). The pump source was a semiconductor laser with an external resonator operating in a continuous single-frequency mode and having a spectral linewidth of 500 kHz. The pump power was 50 µW at a beam aperture of 2 mm2. The radiation receiver was a photodiode with a reduced dark current level [11,12]. To increase the vapor density of the working substance, the cell was heated to a temperature of 100 °C. Fig. 5 shows the absorption spectra of laser radiation for two cells: a reference cell (not shown in Fig. 4) containing a mixture of 87Rb and 85Rb isotopes (top) and microfabricated cell (bottom). A considerable broadening of absorption lines of 87Rb atoms in the microfabricated cell (more than 1 GHz) (see Fig. 5, lines 5 and 6) was due to a high temperature and the presence of the buffer neon gas in the cell having a relatively high pressure (100 mmHg). The 20–50% level of the resonance absorption of the incident radiation indicated that the amount of 87Rb atoms in the cavity was high enough to observe a CPT signal.