In ring laser gyroscopes, the most important error term is the angular random walk. The accuracy of inertial navigation systems is ultimately determined by this error term. For the mechanically dithered ring laser gyroscope, the angular random walk mainly includes random lock-in crossing and quantum noise. Developments in manufacturing techniques, such ultra-smooth surface polishing, are reducing lock-in crossing error and amplifying the significance of quantum noise. Recent studies have demonstrated that the accuracy of high-precision mechanically dithered gyroscopes can nearly achieve quantum noise accuracy. Thus, the next challenge in laser gyroscope research is to compress the quantum noise. From the demonstration of the first laser gyroscopes in the 1960s, most laser gyroscopes operate at a wavelength of 633 nm, owing to the 633 nm spectral line having the largest gain coefficient, compared with its neighboring spectral lines, which facilitates the startup and maintenance of the laser. Hence, a new ring laser gyroscope based on 543 nm is built to discover the relationship between wavelength and quantum noise. The first effect of altering the working wavelength is realized in the variation of scale factor. Moreover, altering the wavelength may result in variations of the number of photons in the resonant cavity, which may alter the quantum noise. Thus, changing the wavelength of the gyroscope can provide information on the mechanism of quantum noise and offer guidance for further quantum noise compression.

The 633 nm spectral line is generated by an energy level transition from 3S₂ to 2P₄, and the 543 nm spectral line is generated by an energy level transition from 3S₂ to 2P₁₀. Under identical conditions, the gain of 543 nm is only 1/30 of that of 633 nm. Once the dominant 633 nm spectral line starts lasering, costs are incurred in terms of population inversion resources, which makes it more difficult for other spectral lines to laser. To achieve the selective oscillation of the 543 nm spectral line, the traditional method is to add optical components to achieve frequency selection. However, to reduce cavity loss, it is necessary to avoid inserting intracavity components in a ring laser gyroscope. Therefore, it is feasible to achieve the desired wavelength oscillation through the selectiveness of the reflecting mirror. Considering that the infrared spectral lines of 3.39 µm and 1.15 µm are also easy to laser, the suppression of 3.39 µm and 1.15 µm is also important, in addition to considering the suppression of 633 nm spectral line. A modification of the resonant cavity is also necessary to achieve 543 nm oscillation. The radius of the diaphragm is recalculated, considering the altered wavelength. In addition to considering the wavelength reduction, the radius of the discharge tube is further reduced to increase the gain. Moreover, the length of the discharge tube is also extended.

Following the construction of the 543 nm ring laser, a light intensity damping device is built to measure the cavity loss. The cavity quality factor can be obtained by observing the exponential decay. Taking advantage of the high reflective film coating, the total cavity loss can reach as low as 1.19×10^-4, which is less than the typical reported cavity loss. The output intensity reaches its maximum of 22.4 μW at a gas pressure of 2.63 Torr, which is lower than that of the 633 nm wavelength, when the He and Ne partial pressure ratio is 20∶1. The frequency tuning characteristics are investigated at various discharge currents. Moreover, when the current is below 1.0 mA, the intensity in the single mode position is lower than that in the multimode position, which causes the path length control circuit to work abnormally. When the current exceeds 1.2 mA, the intensity in the single mode position is higher than that in the multimode position, and the path length control circuit can make the cavity work at the expected position. The 1.4 mA current is selected because a high intensity contrast can improve the precision of the path length. The Sagnac effect is successfully observed after combining the counterpropagating beams. The static performance shows that the angular random walk can reach as low as 4.5×10^-5(°)/h. Although the gain of 543 nm is only 1/30 of that of 633 nm, the random walk can reach the same level.

Most laser gyroscopes currently used in engineering practice employ the red 633 nm spectral line because it has a relatively high gain coefficient. To explore the influence of wavelength on quantum noise, a new green light laser gyroscope based on a wavelength of 543 nm is designed. To overcome the weak gain of the 543 nm spectral line, a narrow banded high-reflective reflector is designed by ion beam coating to suppress spectrum lines such as 633 nm and 3.39 µm. The resonant cavity is also redesigned according to the demands of 543 nm. The cavity ring down method was used to achieve extremely low cavity loss measurement, and the results show that the total loss of the new designed cavity is only 1.19×10^-4. To obtain the maximum light intensity, the partial pressure ratio is set to 20∶1, and the pressure is set to 2.63 Torr. When the discharge current is set to 1.4 mA, the path length control can make the 543 nm gyroscope work steadily at the right position in the single longitude mode. Moreover, the Sagnac effect is successfully observed after combination. Static testing shows that the angular random walk can reach 4.5×10^-5(°)/h, which is the same performance level achieved by 633 nm gyroscopes. Because this is the first realization of a 543 nm wavelength laser gyroscope, there is still further optimization to be completed, including that of the resonant cavity design. The work presented in this study lays the foundation for achieving quantum noise reduction in laser gyroscopes.