Why use A.O?

The turbulence introduced by the atmosphere degrades the images taken by telescopes. Adaptive optics is an effective solution for recovering a large part of the information that is lost. As a result, AO makes it possible to increase the number of scientific observations.

Among the specific parameters linked to astronomy, we may mention:

• the low photon flux
• the high frequency of atmospheric turbulence
• the presence of large spatial frequencies because of atmospheric turbulence.

Products specifically designed for astronomy (large inter-actuator stroke, high frequency and ultra-sensitive) are available from ALPAO. Click on the tabs at the top of the page to learn more about them.

 

Deformable Mirrors

ALPAO has developed two ranges of deformable mirrors for astronomy:

• The range High-Speed Magnetic Deformable Mirror Series allowing the correction of atmospheric turbulence,
• The range Low Speed Magnetic Deformable Mirror Series intended for use in the laboratory in order to validate concepts or generate low-order aberrations.

 

 

 

Hi-Speed deformable mirrors : large strokes and exceptional temporal response

The mirror range Hi-Speed Magnetic Deformable Mirrors is characterised by unrivalled strokes for generating both low-order aberrations and high-order aberrations such as the waffle mode (push/pull) .

The Hi-Speed ALPAO deformable mirrors range offers very large strokes for generating low-order aberrations as well as for high-order aberrations such as waffle mode. These unrivalled strokes are available for distances between actuators of 1.5mm and 2.5mm.

Typical stroke obtained while applying currents (20% of maximal stroke) on 3x3 actuators (mirror suface, half of the wavefront value)

Typical inter-actuator stroke obtained by applying the same absolute command to all the actuators (20% of full stroke).

 

Typical temporal response

These deformable mirrors combine large strokes with high bandwidth. Indeed, thanks to a patented innovation, the mirrors have a stabilisation time in the order of a millisecond. The excellent temporal performance of ALPAO's Hi-Speed mirrors allows the temporal errors traditionally present in large-stroke mirrors to be minimised, thus offering unparalleled image quality.

Thanks to a very short distance between actuators, it is possible to construct extremely compact instruments.

A new electronic system, scalable to 1024 channels (32x32), has been specially designed in order to exploit the full potential of ALPAO's deformable mirrors. Thanks to the control of the current applied to each actuator, the stability achieved is unparalleled.

In addition, it is possible to order several deformable mirrors with a single electronics system (and a single computer). For example, using a 1024-channel electrical system, it is possible to control several deformable mirrors with only one drive electronics. This makes it easier to implement complex configurations such as those found in the Multiple Objects Adaptive Optics (MOAO) or Multi-conjugate Adaptive Optics (MCAO) modes.

 

The characteristics of the Hi-Speed DM Series mirror range are summarised in the following tables. Each table corresponds to a given distance between two actuators (1.5 and 2.5mm). For more information you can contact us via the site (click here) or by phone or you can download the datasheet in the Downloads section.

1.5mm between two actuators

2.5mm between two actuators

(1)-> in closed loop

(2)-> All ALPAO mirrors can be coated with different metallic materials (silver, aluminium, gold,...).

(3)-> Mirrors working at -40°C are also available. Contact us for more information

 

Low Speed DM: entry-level deformable mirrors for astronomy

The range Low Speed Deformable Mirror Series consists of 2 deformable mirrors (52 and 88 actuators). This range has been designed to start off research and development activities in astronomy. In addition, it is possible to use these mirrors as generators of aberrations or as woofers in a woofer/tweeter configuration.

The Low Speed DM52-25 is the smallest deformable mirror. A continuous membrane (15.0mm useful pupil diameter) is deformed by 52 miniaturized voice-coil actuators. As there is no contact between the membrane and the coil array, large deformations are possible without degrading the optical quality (50µm peak-to-valley stroke).

See the datasheet for more information. Special designs based on the off-the-shelf Low Speed DM are available on request.

The characteristics of the range Low-Speed DM Series are summarised in the following table.

(1) In closed loop

(2) A low-temperature version (-40°C) is also available.

(3) Metallic coatings available (silver, aluminium, gold, etc.)

The figure here after shows the typical wavefront Zernike mode achievable (peak-to-valley wavefront amplitude) with the Low Speed DM88-25.

The figure here after shows the typical wavefront Zernike mode achievable (peak-to-valley wavefront amplitude) with the Low Speed DM52-25.

> Click here to contact us and get more information about our deformable mirrors

 

Wavefront sensor

The Shack Hartmann wavefront sensors manufactured by ALPAO have been optimised for low photon flux applications such as astronomy. Thanks to our ACE software architecture, the user benefits from excellent performance while working in a powerful and flexible environment such as Matlab® or Labview®.

These wavefront sensors are optimised for closed-loop adaptive optics applications. In particular, to optimise the signal-to-noise ratio, the framework of micro-lenses is tailored to the number of actuators (Fried configuration).

	ALPAO sh49	ALPAO sh81	ALPAO sh100	ALPAO sh256
Lenslet array	7x7	9x9	10x10	16x16
Dynamic (tip/tilt)	125λ	90λ	72λ	23λ
Accuracy	λ/50	λ/75	λ/75	λ/100
Frame rate from Matlab®	> 495 fps	>495 fps	> 495 fps	> 495 fps
Recommended deformable mirror	Hi-Speed DM52-15	Hi-Speed DM88-25	Hi-Speed DM97-15	Hi-Speed DM241-25

These wavefront sensors use an extremely sensitive EMCCD detector implemented in a camera manufactured by Andor Technologies. The principal technical characteristics of the camera are summarised below.

Active Pixels	128x128
Pixel Size (µm)	24
Image Area (mm x mm)	3.1 x 3.1
Active Area Pixel Well Depth (e-, typical)	Typical: 160 000 Maximum: 220 000
Gain Register Pixel Well Depth (e-, typical)	800 000
Max Readout Rate	10 MHz
Frame Rate (Frames Per Second from Matlab®)	> 495
Read Noise (e-, typical)	< 1 to 48 @ 10 MHz

If you cannot find the wavefront sensor corresponding to your needs, contact us by clicking here or by calling us on +33 4 76 89 09 65.

Full systems

Our adaptive optics systems are based on the ALPAO Core Engine control architecture which has been designed for three goals

1. high performances
2. flexibility
3. to enable user creativity

ALPAO proposes two ready out-of-the box A.O. systems for astronomy which are described below:

• AOS-0 which has been designed for R&D in the field of adaptive optics.
• AOS-1 which is high performance system for astronomical observations.

Furthermore, thanks to our strong background in astronomy we are able to design custom A.O. systems for 1 meter and 2 meter class telescopes in function of the goals of the adaptive optics and the specificity of each observation instrument.

 

ALPAO AOS-0: Flexible R&D Toolkit for adaptive optics system

This plug-and-play system has been specifically designed for:

1. Engineers and Scientists studying adaptive optics control and real-time processing,
2. Training purposes.

The standard package includes all parts required to simulate a complete adaptive optics system with the aberration generator:

• an ALPAO Hi-Speed DM52-15 deformable mirror with its drive electronic
• a Shack-Hartmann wavefront sensor
• an imaging camera
• a turbulence phase screen with its rotating mechanism
• a light source 
• all opto-mechanical parts
• a set of procedures to drive the system from Matlab® 
• a Matlab® licence (if needed by the user).
  

The flexible ALPAO CORE ENGINE (ACE) allows developping approaches ranging from a standard closed-loop up to upmost advanced laws such as Kalmann filtering. The easy access to the data (wavefront error, command matrix, measurement matrix,...) makes easier the development of your project.

Furthermore, wavefront sensors are usually used to closed the loop. Thanks to the ACE modular approach, you can also close the loop using the imaging camera and iterative algorithms within a few line of code without using the wavefront sensor. As the development environments chosen by ALPAO are widely spread, users benefit from all the community support over the Internet.

A set of standard programs are delivered for training purpose, demonstrating all the benefits of adaptive optics and the way it works. With AOS-0, there is no need to become an expert in adaptive optics and real-time signal processing. But if you want to, you can !

> Click here for more information

 

AOS-1: high performances adaptive optics for astronomy

The AOS-1 features:

• a Hi-Speed 241-25 Deformable Mirror having a diameter of 40mm with 17x17 actuators located on a rectangular grid.
• an ultra-sensitive wavefront sensor manufactured by ALPAO and based on an EMCCD camera and having 16x16 micro-lenses (Fried configuration).
• a real time computer to close the loop at a frame rate of 500Hz based on the ALPAO Core Engine (ACE).

> Click here for more information

 

References & Examples

Solar observation

The images shown hereafter have been obtained by Dr. Miura at the Hida observatory with a 60cm telescope and a Hi-Speed DM97-15 deformable mirror. More information can be found out in:

N. Miura, "Solar Adaptive Optics System and Observations at the Hida Observatory," in Imaging Systems Applications , OSA Technical Digest (CD) (Optical Society of America, 2011), paper JWA26

N. Miura, "Solar Adaptive Optics System and Observations at the Hida Observatory," in Imaging Systems Applications , OSA Technical Digest (CD) (Optical Society of America, 2011), paper JWA26.

N. Miura et al., "Solar adaptive optics system at the Hida observatory", Proc of SPIE 2008, Paper 7015-249, To be published.

O. Lardiere, R. Conan, C. Bradley, G. Herriotb, K. Jackson, " Laser-Guide-Star wavefront sensing for TMT: Experimental results of the Matched Filtering", Proc of SPIE 2008, Paper 7015-174, To be published.

A. Costille, C. Petit, JM Conan, T. Fusco, C. Kulcsar, HF Raynaud, "Optimization of MCAO performance: experimental results on ONERA Laboratory MCAO bench", Proc of SPIE 2008 paper 7015-152. To be published

E. Laag, D. Gavel, M. Ammons, "Open-loop woofer-tweeter control on the LAO multi-conjugate adaptive optics testbed", APS arxiv, october 2007

R. Conan, C. Bradley, P. Hampton, O. Keskin, A. Hilton, and C. Blain, "Distributed modal command for a two-deformable-mirror adaptive optics system," Appl. Opt. 46, 4329-4340 (2007)

Onur Keskin, Peter Hampton, Rodolphe Conan, Colin Bradley, Aaron Hilton, Celia Blain, "Woofer-Tweeter Adaptive Optics Test Bench," ahs, pp. 74-80, First NASA/ESA Conference on Adaptive Hardware and Systems (AHS'06), 2006

Examples made by ALPAO

• ALPAO has deveveloped a high performance COTS adaptive optics system for R&D in astronomy. More information can be found out at this page.

 

> Click here for more information