Wavemeter FAQ: pros and cons



The MOGLabs WaveMeter (MWM002) is unlike most other wavemeters on the market.  It has many good properties but also some limitations in comparison with Fizeau and Michelson wavemeters.  You should be clear about those before considering whether the MWM is right for you.
The bad
The relative accuracy is very good; for example a customer measured the 6.8GHz separation of rubidium ground-state hyperfine levels to better than 20MHz.  Laser wavelength changes of 0.1pm (100MHz) can be measured, and the MWM is perfect for tuning off-resonance dipole trapping lasers.

The absolute accuracy of the MWM is at best ±0.001nm (i.e. ± 1pm, or 1GHz) immediately after calibration, but a more pragmatic expectation is ten times worse than that, i.e. ±0.01nm if moving the device from lab to lab, or through sudden temperature changes, or prolonged humidity changes.  See the data below, for a wavemeter calibrated in an office then moved to a laboratory where it was used to measure the wavelength of a frequency-stabilised laser.  The measured wavelength shifted quickly and then settled down to within a +/- 1pm band for three weeks, despite air conditioning failure (day 3; device temperature increased from 25 to 31 °C) and relocation in the lab on day 16.

The absolute accuracy is generally sufficient to tune a laser to an atomic resonance.  A typical ECDL (external cavity diode laser) has a mode-hop-free tuning range (MHFR) of at least 10GHz.  The MWM can tune within the laser MHFR of resonance, and scanning the laser will then find the resonance.


The MWM operates over a limited wavelength range, for example 775nm to 796nm.  If you need to work at a different wavelength, a mechanical adjustment and recalibration are required.  The centre wavelength can be adjusted from 350nm to 1120nm.  Recalibration requires a light source with known wavelength.

The MWM does not have an internal calibration source to correct for ageing and drift.  In most cases your experiment will provide you with very good calibration. For example, if you are locking your laser to an atomic transition, once the laser is locked, you can recalibrate to that wavelength with a single click.
The good
The MWM gives you picometre resolution with picowatt sensitivity – at a picoprice!

As mentioned above, the relative accuracy (of order 20MHz plus 0.005%) is comparable to extremely expensive Fizeau or Michelson wavemeters.

The MWM002 is just $3090 (USD, introductory price, including shipping).  Fizeau and Michelson wavemeters are more than five times that.  If you just want to tune a laser to an atomic transition, the MWM is more than good enough.​

The MWM operates even with 1pW (picowatt).  It is so sensitive you don’t need a fibre coupler: just hold the end of the singlemode fibre in the laser beam.  Even with a business card between laser and fibre facet, you still have plenty of power.

The MWM can show multiple frequencies simultaneously, for example clearly showing multimode behaviour with ECDLs, or showing several lasers simultaneously provided they are separated by more than the optical resolution (typically 0.02nm at 780nm) and of course they must be within the operating wavelength range.  You can also measure your laser ASE (i.e. the background emission outside the central laser line).  The software provides a simple HDR (high dynamic range) measurement with over 50dB dynamic range.

The MWM operates over USB and Ethernet.  Only one copy of the software is required to operate multiple wavemeters on one computer.  All of the device-relevant information is stored on each device.

LCD display
A small LCD display shows the measured wavelength, so you don’t have to look across the lab to your computer when you’re adjusting your laser.

Size and power
The MWM is compact (165 x 85 x 70mm) and runs from USB power alone (<300mA).  It can be battery-operated.

Did we mention the price?  If you have $20,000 for a wavemeter then certainly a good Fizeau wavemeter with internal calibration is a great thing to have.  If you just need to tune your laser to the same atomic transition (and most labs work with only one atom and transition) then why not spend the same on a MOGLabs MWM and get a rock-solid MOGLabs cateye laser included?  Or buy a wavemeter for every one of your lasers and you can monitor the wavelength of each from your central data acquisition computer.