Pseudoheterodyne Optical Detection
Applications: Scanning near-field optical microscopy (SNOM, NSOM), laser spectroscopy, photonics
Sub-wavelength resolution imaging with SNOM and laser spectroscopy on small sample quantities require a sensitive detection due to the weak optical measurement signal. Best sensitivity in linear detection is achieved with interferometric lock-in techniques, where the weak measurement signal is mixed onto a modulated reference beam and analyzed with a lock-in amplifier. In pseudoheterodyne detection, the reference beam is phase-modulated and at least two harmonics of the modulation frequency need to be analyzed.
The sensitivity of pseudoheterodyne detection is enhanced by two orders of magnitude compared to non-interferometric techniques. Furthermore the interferometric detection technique preserves optical phase information, therefore providing a deeper insight into the structures under investigation.
| Objectives: | perform lock-in assisted, phase-resolved low light (lower femtowatt regime) measurements that require multiple harmonics of the modulation frequency to be analyzed due to the pseudoheterodyne detection scheme |
| Benefits: | integrated solution for demodulation of 3 different harmonics of the phase modulation stimuli for each of the two channels |
| Relevant products: | HF2LI, HF2LI-MF, HF2LI-MOD, HF2LI-PLL |
HF2LI Pseudoheterodyne Optical (SNOM) Detection Setup
Key Features of the HF2LI Lock-in Amplifier for this Application
- Demodulation of 3 harmonics per channel
- Fast auxiliary outputs for data acquisition in the SPM controller
- LabVIEW, C, Matlab, Python programming interfaces for instantaneous monitoring of the optical amplitude and phase, which facilitates the optical alignment procedures in SNOM
- Phase modulation between kHz and MHz range, where the laser noise is lower than at kHz frequencies