The one-time up-return cementing technology is used to cement long open holes of gas wells,having advantages of shortening drilling cycle,reducing drilling cost,eliminating the problem of decreasing the bearing capability of casing string which is often caused due to the use of stage collar,and ensuring the cementing quality in gas zone sections.

To compensate of the nonlinearity error of heterodyne interferometers in nanometer measurement,a method for reducing the first harmonic nonlinearity is proposed.

If the frequency of a laser is modulated sinusoidally, the first harmonic component of saturated absorption signal can be used as error signal to stabilize the frequency of the laser.