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Entry   Menhir pulsed laser locking, posted by Xinyi Lu at Optical room about lasers and optics Screenshot_2024-02-21_1_110931.pngScreenshot_2024-02-21_110934.pngcalculation.jpg
    Reply   Menhir pulsed laser locking, posted by Xinyi Lu at Optical room about lasers and optics Relative_cavity_gain_vs_CEP.pngGain_vs_CEP.m
       Reply   Menhir pulsed laser locking, posted by Xinyi Lu at Optical room about lasers and optics Gain_vs_CEP.pngScreenshot_2024-02-23_0_183652.png
          Reply   Menhir pulsed laser locking, posted by Xinyi Lu at Optical room about lasers and optics Gain_vs_CEP.m
Message ID: 192     Entry time: Mon Feb 26 08:58:33 2024     In reply to: 191     Reply to this: 193
 Author: Xinyi Lu 
 Status: Fixed 
 Type: info 
 Category: lasers and optics 
 Location: Optical room 
 Title: Menhir pulsed laser locking 

Last week, Ronic and I focused on CEP measurements of the menhir laser.

  1. Measurements without Cavity Locking:
    • Direct measurement of repetition rate (Frep) with a spectrum analyzer. Altering the laser pump current from 950mA to 850mA, Frep changed by +28Hz.
    • Measurement of the variation of carrier-envelope frequency (Fceo) by beating with CW laser. Altering the laser pump current from 950mA to 850mA resulted in a beating frequency of n0*dFrep + dFceo = +/-2.4MHz, so dFceo ~ 50MHz.
  2. Measurement with Cavity Locking:
    • Maintaining cavity locking, we changed the laser pump current and AOM frequency to record the transmitted power of 5 consecutive fundamental mode (TEM00) resonances.
    • The pump currents were set to 850 mA, 900 mA and 950 mA, and the AOM frequency were set to 210 MHz and 250 MHz. We then plotted the measured transmission amplitude values against the theoretical gain curve (see Figure 1).
    • By adjusting the CEP, we reach the top point on the curve, which is the maximum gain. At this point, the coupling frequency increases from 10% to 50% (see Figure 2).
    • We observe that a 100mA change in pump current adjusts the CEP for pi/2, while changing the AOM frequency by +/-40MHz adjusts the CEP for pi. In summary, our CEP tuning range is about 3pi/2 (130 MHz) - not the full 2pi, but still probably giving us maximum gain.
  3. Next Steps:
    • Investigate factors associated with changes in CEP, such as laser temperature or pressure.
    • Discuss with Menhir the feasibility of expanding the laser pump current adjustment range (now limited to 100mA).
    • Optimize AOM frequency and locking status, connect the amplifier.
Xinyi Lu wrote:

Here is a simulation of the relative FP-cavity gain vs the CEP for a Finesse of 23000 and taking into account the Menhir laser optical spectrum and several CVBG parameters.

I added the commented Matlab code to produce this plot.

Xinyi Lu wrote:

These days, Ronic, Daniele and I achieved stable cavity locking with the menhir pulsed laser.

- After vacuuming, the current cavity finesse is now about 23,000. The diameter of the cavity mode is w_x=2.2mm, w_y=2.7mm.

- We had to compensate for frequency drift by manually adjusting the cavity length to keep locking.

Now the problem is that CEP's compensation range is not enough. The laser CEP is drifting from day to day. We adjusted the CEP by tuning the pump current of the menhir laser, but the adjustment range was not enough.

- The laser pump current is varied in the locking state and the variation of repetition rate is recorded. The current range is 850mA to 950mA and the repetition rate changes by 24 Hz. The calculation process is shown in Figure 3.

- By calculation, the variation of CEP caused by the variation of laser current is only π/2, which we hope is 2π.

- For Gamma Factory, the target FSR is 40 MHz, so the 4-pulse stack provides 4 times CEP tuning range to meet the requirements. But for our experiment, it seems not enough now.

The next step is to evaluate the gap to the maximum gain and draw the curve of CEP. Then we will discuss solutions.

 

 

 
 

 

 

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