[Tanaka,Chen,Yu,Saito]

We fitted the beam profile measured after the first lens in klog:36752. The deviations of the fitted values from the calculated values were 0.2% for the waist position and 7% for the waist size. Next, we measured and fitted the beam profile after the second lens. The deviations from the calculated values were 0.1% for the waist position and 2% for the waist size.
We also measured the absolute frequency of the sub-laser using a wavelength meter.
 

• We fitted the beam profile measured after the first lens in klog:36752 (Fig. 1). The points represent the measured data, and the line represents the fitting result. The green and orange points were used for the fitting, while the blue and red points were not used. The origin corresponds to the position where the laser is emitted. Since the recommended measurement range of the beam profiler is a beam diameter of 45 μm to 4 mm, data points with a beam radius exceeding 2 mm were excluded from the fitting. The calculated values from klog:36739 and the fitting results are as follows:

  Calculated values: waist position = 3008.7 mm, waist size = 0.0112 mm
  Results (average): waist position = 3014.5 mm, waist size = 0.0120 mm

  The deviations of the averaged results from the calculated values were 0.2% for the waist position and 7% for the waist size. Since the errors were small, we proceeded to measure the beam profile after the second lens. First, we placed the beam profiler at the calculated waist position and adjusted it so that the waist size matched the calculated value. Then, we measured and fitted the beam profile after the second lens (Fig. 2). The calculated values from klog:36739 and the fitting results are as follows:

  Calculated values: waist position = 4066 mm, waist size = 0.054 mm
  Results (average): waist position = 4062 mm, waist size = 0.055 mm

  The deviations of the averaged results from the calculated values were 0.1% for the waist position and 2% for the waist size. Since the errors were small, the lens positions were finalized.
   

• To measure the absolute frequency of the sub-laser, we placed a wavelength meter on the transmission side of the beam sampler (Photo 1). The input power to the wavelength meter was adjusted to approximately 1 mW by tuning the HWP before the FI. The laser settings before the measurement were as follows:

  Current: 1.776 A
  Temperature: 24.75 ℃

  The absolute frequency of the sub-laser  was measured while changing the temperature in steps of 0.5 ℃ (Fig. 3). The origin of the vertical axis is 281630 GHz.
  After the measurement, the laser temperature was returned to its original value.