Saturated absorption spectroscopy (SAS) is a common technique for locking and stabilizing lasers via atomic transitions.

However, setups vary depending on the wavelength of the laser etc. For instance, SAS at 420nm using Rb often requires heating the cell to increase the signal for locking, while often SAS at 780nm with Rb does not.

SAS library:

• 420nm Rb SAS with heater
• 780nm Rb SAS

• Input Alignment:

  • Two optional input mirrors for downstream alignment.
  • A half-wave plate to branch off power via a polarizing beam splitter (PBS).

• Probe Beam:

  • A beam sampler reflects a small fraction of the light to transmit through the Rb cell as the 'probe' beam.
  • A half-wave plate rotates the vertical polarization to horizontal, allowing the probe beam to pass through the PBS and be detected by the photodiode.

• Pump Beam:

  • The majority of the light transmits through the beam sampler becoming the 'pump' beam.
  • The vertically polarized pump beam then reflects off the PBS, counter propagating the pump beam.

• Optional Features:

  • The pump power can be reused by fiber coupling to a wavemeter.

To lock we use both Toptica software as well as the open source Linien Locking Tool running on a Red Pitaya.

Details of layout:

Instructions for setup:

These layouts can be recompiled at arbitrary scales by calling different dictionaries for components. For example, this shows the same SAS code being compiled with 1 inch, 1/2 inch and miniature optics etc.

420nm_Rb_Saturation_Absorption_Spetroscopy.step

420nm_Rb_Saturation_Absorption_Spetroscopy_topview.pdf

To increase the signal to noise of the Rb spectrum, we heat the vapor cell to over 100C. Insulating the cell make it easier to heat, so we use a 3D printed enclosure to hold the Rb vapor cell made from 'High temperature' SIRAYA Tech Professional UV Resin.

• rb_cell_holder_base.stl

• rb_cell_holder_top.stl