Subsequently the bandwidth increases with increasing the cell temperature. The bandwidth depends on the transverse www.selleckchem.com/products/brefeldin-a.html relaxation time ��2, as evident from (4) and (6). An increase in the cell temperature increases the vapor pressure, which results in a larger number of atoms interacting with the light, leading to a longer relaxation time (smaller bandwidth). However, at high temperature, the number of collisions between atoms or with the walls of the cell increases significantly, leading to a shorter relaxation time and hence a larger bandwidth. This explains the existence of a critical temperature (around 45��) at which the intrinsic bandwidth is minimum. Figure 8Intrinsic bandwidth versus cell temperature for an input optical light power of 10��W, 15��W, and 20��W.
In the experiments, the measured maximum bandwidth was 175Hz, obtained at room temperature (23��C) with an input optical power of 10��W (blue curve in Figure 8), while the minimum bandwidth was 25Hz, obtained with an input optical power of 20��W at a temperature of 45��C (black curve in Figure 8).4.3. Low-Amplitude Magnetic Field MeasurementThe ultimate intrinsic sensitivity of the magnetometer can be calculated using (5). The best performance of the magnetometer was obtained for an input optical power of 20��W at cell temperature of 48��C; the ultimate intrinsic sensitivity was 327fT/Hz1/2 over a bandwidth of 26Hz. However, the external magnetic noise generated by power lines and surrounding equipment caused the actual ultimate sensitivity of the magnetometer to drop to 130pT/Hz1/2 over a bandwidth of 26Hz.
The magnetometer in its optimal configuration (input optical power of 20��W at cell temperature of 48��C) was then used to measure an applied small-signal sinusoidal magnetic field of amplitude 15pT oscillating at 25Hz, which was generated by a test coil placed at a distance of 6cm from the vapor cell. For this measurement, the uniform dc magnetic field was 13��T, corresponding to a Larmor frequency of 45.5kHz. The frequency of the rf magnetic field was then set at 45.5kHz resulting in a phase shift of ?90 degrees between the photodiode output and the driving rf signal, as predicted by (4), and verified experimentally by the result shown in Figure 7(c). When another 25Hz small-amplitude magnetic field was applied in addition to the dc and rf magnetic fields, the Larmor frequency changed and no more resonance occurred, Cilengitide causing the phase shift between the photodiode output and the driving rf signal to oscillate around ?90 degrees at 25Hz. This enabled the measurement of the new Larmor frequency and hence the calculation of the magnitude of the 25Hz small-amplitude magnetic field, which is proportional to the new Larmor frequency.