# Comparing focal plane wavefront control techniques:\\Numerical simulations and laboratory experiments

**Authors:** Axel Potier, Pierre Baudoz, Raphaël Galicher, Garima Singh, Anthony Boccaletti  
**arXiv:** [2003.04336](https://arxiv.org/abs/2003.04336)  
**Date:** 2020-03-09  
**Summary page:** https://www.summarizepaper.com/en/arxiv-id/2003.04336v1/

## Key points

- Spectroscopic observations are crucial for understanding exoplanet physical properties
- Less than 1% of detected exoplanets have been characterized through spectroscopy
- High-contrast imaging techniques offer an alternative by separating light from off-axis sources, providing access to atmospheric signatures
- Future space facilities like WFIRST/LUVOIR/HabEX will use coronagraphic instruments for imaging and spectroscopy
- Precise control of wavefront phase and amplitude errors is a major technological challenge in instrument design
- Various focal plane wavefront sensing (FPWS) and control techniques have been proposed and demonstrated in labs
- A recent study compared pair-wise (PW) with electric field conjugation (EFC) and self-coherent camera (SCC) techniques in visible light using simulations and experiments
- Both PW+EFC and SCC were able to minimize speckle intensity in coronagraphic images effectively
- Both techniques reached laboratory bench limitations, achieving contrast levels as low as 5e-9 in a narrow spectral band (<0.25% bandwidth)

## Summary

In the field of exoplanet characterization, spectroscopic observations are crucial for understanding the physical properties of distant worlds. However, less than 1% of all detected exoplanets have been characterized in this way. High-contrast imaging techniques offer a promising alternative by allowing the separation of light from a faint off-axis source and its parent star, providing access to atmospheric signatures. Future space facilities such as WFIRST/LUVOIR/HabEX are expected to utilize coronagraphic instruments capable of both imaging and spectroscopy to further our knowledge of these distant worlds. One major technological challenge in designing these instruments is the precise control of wavefront phase and amplitude errors. Various focal plane wavefront sensing (FPWS) and control techniques have been proposed and demonstrated in laboratory settings to achieve the required accuracy. However, these techniques have not been directly compared under identical conditions until now. A recent study compared two wavefront control techniques – pair-wise (PW) associated with electric field conjugation (EFC) and self-coherent camera (SCC) – in visible light using numerical simulations and laboratory experiments. The researchers optimized PW wavefront sensing through simulations to predict the performance of a coronagraphic instrument with PW+EFC wavefront control, accounting for modeling errors in both techniques. The experimental setup involved introducing known aberrations into the system and comparing wavefront sensing using PW and SCC. Subsequently, both PW+EFC and SCC were independently used to minimize speckle intensity in coronagraphic images. The results showed that both SCC and PW+EFC could generate a dark hole in space-like conditions within a few iterations. Overall, both techniques reached the current limitations of the laboratory bench, achieving coronagraphic contrast levels as low as 5e-9 in a narrow spectral band (<0.25% bandwidth). This study provides valuable insights into the capabilities of different wavefront control techniques for future exoplanet characterization missions.