Aligning the Mira Laser
Notes related to power and alignment of a Coherent Mira Optima 900-F

Coherent Laser

Improving Mode Lock

  • Power-on the laser as described in the start-up sequence. Do not mode-lock the laser.
    • Familiarize yourself with all of the knobs (their labels and positions)
    • Note the continuous wave (CW) and mode lock (ML) positions of the far left switch, as well as the range/reset switch
  • Maximally open the aperture (slit) by rotating the width adjustment knob clockwise until maximum power is observed (as shown by the number on the far left of the display under the oscilloscope). This is often near 400. “Auto Range” or “Range Reset” may need to be toggled to optimally view power during this adjustment.
  • Close the aperture (slit) to achieve 50% power by rotating the same knob you just adjusted counter-clockwise until the number on the display is half of maximum. This is often around 200.
  • Adjust aperture translation for maximum power by rotating the slit horizontal translation adjustment knob in either direction to achieve maximum intensity as measured on the device below the oscilloscope.
  • Adjust the beam pump position by rotating the pump beam steering knobs (just the right two) for maximum intensity.
  • Set the end mirror tilt angle by rotating the end mirror controls to maximize power output.
  • Assess the purity of the sine wave. If it is pure, it will mode-lock easily. If not, go back to the aperture adjustment step. This may need to be done a few times.

Additional notes: I have found that I get better results if, once mode locked, I slowly decrease laser intensity (by adjusting the iris) back down to 200. As I do this, I often lose mode lock, so I re-establish mode lock, twiddle ALL the knobs to maximize the intensity of the mode-locked peak, then slowly narrow the iris again. After doing this 6-8 times, the laser will mode lock really easily (even though the original sine wave looks surprisingly small, and of the wrong frequency), and the mode-locked laser power will be a steady 200.

Photos and Diagrams

Adjustments

Left side

Right side

Not Locked

Mode Locked

Suggested Waveform

Ideal output spectrum and power

Micrometer Wavelength Adjustment

On 2018-10-19 the micrometer was adjusted to tune the laser to 810nm. This is the reading at optimal tuning position.