Ultra Sensitive Laser
Noise Characterization

Measuring, analyzing and controlling
laser linewidth and lineshape spectra

HighFinesse
Linewidth Analyzer

The superb sensitivity of the LWA-1k is achieved by combining an interferometric working principle with high-end optical and electronic components.

1. Laser
2. Frequency discriminator (interferometer)
3. Photodetector
4. Analog electronics
5. Data acquisition system
6. Computer

The laser light (1) is coupled to the input fiber and lead through an interferometer (2) acting as a frequency discriminator.

Photodetector and our analog electronics

The transmitted intensity, which is directly proportional to the variations of the input frequency, is converted by a photodetector (3) and our analog electronics (4) into a voltage signal.

This voltage is finally digitized by the Digitizer (5) to provide the data for evaluation on a computer (6).

Calculation of frequency noise density spectrum and the optical lineshape spectrum

The included software recovers the original frequency noise using the precisely known interferometer function. The recovered timeseries of the frequency deviations is now the basic dataset allowing to calculate easily the frequency noise density spectrum and the optical lineshape spectrum.

Export timeseries data for custom evaluation methods

The user can also export the timeseries data in order to perform custom evaluation methods such as Allan deviation or coherence time analysis.

Typical Data and Linewidth Evaluation

Timeseries

Frequency noise density spectrum

(1) β-separation line

(2) Area of frequency noise above β-separation line
→ Integration for effective (optical) linewidth estimation

(3) White noise level
→ Noise density level directly proportional to intrinsic (Lorentzian) linewidth

Optical lineshape spectrum

(4) Linefit to optical spectrum
→ Full width at half maximum = effective (optical) linewidth

Active laser noise reduction
with the feedback controller

Due to the design of the LWA-1k, the output voltage can be directly used as an error signal for a feedback controller allowing to reduce the frequency noise of the test laser.

Depending on the used feedback controller and the laser system the optical linewidth can be reduced by more than two orders of magnitude offering a vast amount of new opportunities.

Connect the Analyzer output signal (A) as input signal to a fast feedback controller (1). Connect the feedback controller to the laser’s (2) fast DC modulation input, e.g. laser diode current.

Reduce actively the laser noise by adjusting the feedback to minimize the output signal of the Analyzer (e.g. PID parameters, gain).

Ultra Sensitive Laser
Noise Characterization

Measuring, analyzing and controlling
laser linewidth and lineshape spectra