Imagine Optic https://www.imagine-optic.com/ Wavefront Sensing, Optical Metrology & Adaptive Optics Fri, 05 Jul 2024 07:47:03 +0000 en-US hourly 1 https://wordpress.org/?v=6.4.5 https://www.imagine-optic.com/wp-content/uploads/2021/02/cropped-favicon-imagine-32x32.png Imagine Optic https://www.imagine-optic.com/ 32 32 Shack Hartmann wavefront sensors: and yet they are achromatic! https://www.imagine-optic.com/shack-hartmann-wavefront-sensors-and-yet-they-are-achromatic/ Tue, 18 Jun 2024 08:59:24 +0000 https://www.imagine-optic.com/?p=267272 The post Shack Hartmann wavefront sensors: and yet they are achromatic! appeared first on Imagine Optic.

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Flat earthers claim that our planet is flat, despite any physical evidence and simple observation. Should we mock those who deny the obvious? Instead, let’s take the time to explain, and justify, on the basis of physical principles.

We have known for a long (very long) time, that earth is round: Aristotle provided first demonstration for a spherical earth in 4th century BC! By the 16th century, navigators had circled it and if scientific demonstrations were not enough, recent space observation of earth brings quite an easy -visual- proof of it.

Nevertheless, there are still a bunch of people to pretend that it is not. Should we mock them? In particular, as the physicists we are? I tend to think that it is a shortcut we should not take, if it’s not for other reasons, at least because it is not the most efficient way to convince and educate.

So when it comes to explain, again and again, that Shack Hartmann Wavefront Sensors are achromatic, I am very happy to do the same. Again, and again. And as physicist, to bring an explanation backed up by demonstration.

So here it goes.

 

Context

 

Shack Hartmann Wavefront sensors as we know them originally comes from an idea of Hartmann, in which a set of pinholes allowed to isolate rays and calculate their direction of propagation. Obviously, no effect of wavelength is questioned in the use of Hartmann masks of holes to reconstruct wavefronts.

Shack then proposed to use lenses instead of holes. As they concentrate light instead of blocking it, it is a much more efficient optical system. Combined with the advent of cameras and modern computers, it made the Shack Hartmann wavefront sensors the reference it is nowadays for wavefront sensing.

But here’s the thing: lenses are chromatic, hence Shack Hartmann wavefront sensors are limited by chromaticity! But that’s a simplification, and as always, the devil is in the details.

Simulations

 

So let’s leave faith or conspiracy theories aside and simulate the behavior of the microlenses array of a Shack Hartmann wavefront sensor at different wavelengths (representative of the sensor’s spectral range of use) and for different wavefront slopes (to mimic the sensor’s measurement dynamic of aberrations).

We use Zemax raytrace software to simulate the optical propagation of 3 incoming collimated beams corresponding to incidence angles of 0°, 1° and 3° sampled by a microlens (figure a). The distance between the microlens and the detector (wavefront sensor array of pixels) is optimized at 635nm.

We plot the various PSFs corresponding the centroid focused by the microlens for 4 different wavelengths: 450nm, 635nm, 850nm and 1050nm. (figure b). We can observe that the diameter of the PSFs increases significantly with wavelength, which is not surprising (we know that the diameter of the focal point is linearly proportional to the wavelength link). The visual effect of chromatism cannot be appreciated on the PSFs: 1/ longitudinally: the chromatic focal length of the microlens and the corresponding defocus do not compensate for the change in diameter of the centroid, 2/ laterally: no effect of the defocus on the shape of the PSF and on its symmetry can be appreciated (one could expect that the defocus combined with the lateral displacement of the centroid for high slopes values might affect the intensity distribution of the PSF).

We then plot the Spot Diagram for each slope and for each wavelength, together with the Airy disk (black circle in figure c) which represents the diffraction limit of the microlens at 635nm. All Spot Diagrams and all Spot Diagram variations due to wavelength changes are clearly well below the diffraction limit of the microlens, which represents its best ability to focus light. Also, the fact that for a given slope, all the Spot Diagrams continue to overlap at all wavelengths suggests that the effect of chromatism on lateral position of the centroid, if it exists, is minimal not only in relation with the Airy disk size but also in relation to the size of the pixels (corresponding to the gray grid in figure c).

 

Analysis

 

Even if the Spot Diagrams -and the absence of visual variations in PSF intensity distribution for the different slopes at different wavelengths- already tell us that the effect of chromatism is marginal in a design representative of a Shack Hartmann wavefront sensor, we continue the simulation analysis by calculating the barycentric position of each PSF. We then compare this position respect with the position of the PSF at 635nm, wavelength for which the system is optimized, and translate position errors in slope errors (see table below).

 

Slope error @635nm [rad] Slope error @635nm [°]
Wavelength (nm) @0° @1° @3° @0° @1° @3°
450 0 7,5E-07 2,3E-06 0 4,3E-05 1,3E-04
635 0 0 0 0 0 0
850 0 -4,0E-07 -1,2E-06 0 -2,3E-05 -6,9E-05
1050 0 -6,0E-07 -1,9E-06 0 -3,4E-05 -1,1E-04

We can observe and quantify the error in slope measurements when combining high slopes values with spanning the spectral range of the sensor. Absolute value is found to be approx. 2urad at the limits of the spectral range, 450nm and 1050nm. Relative value is as small as approx. 0.004%, in the worst case.

 

Conclusion

 

We put a scale on the effect of chromatism even in presence of huge wavefront dynamic and demonstrated that their impact on centroid aspect and centroid lateral position is minimal. We can claim then Shack Hartmann wavefront sensors are achromatic on their whole spectral range such as our HASO4 BROADBAND.

 

We are happy to discuss how they suit your needs. Reach us at contact@imagine-optic.com .

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Laser beam diagnostics: a new approach to ISO 11146 standard https://www.imagine-optic.com/laser-beam-diagnostics-a-new-approach-to-iso-11146-standard/ Mon, 04 Mar 2024 14:42:57 +0000 https://www.imagine-optic.com/?p=267016 The post Laser beam diagnostics: a new approach to ISO 11146 standard appeared first on Imagine Optic.

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Laser beam diagnostics:
What if Star Wars had deployed the ISO 11146 standard for laser beam diagnostics? We can’t rewrite history, but we can still delve into M2 measurement for your laser. (Image courtesy of Lucasfilm)

 

How is laser beam quality measured?

 

Several parameters are very useful to assess laser beam quality and properties. Among them are: M-squared factor (M2), divergence (), width at waist (w0), Beam Parameter Product (BPP), waist location, astigmatism, asymmetry, which can be calculated with conventional M2 beam propagation analyzers.

 

Laser beam quality

To reconstruct these parameters, such systems generally implement a camera that is moved along the laser propagation axis (z), either manually or by means of a translation stage, to acquire intensity maps of the beam. ISO 11146 standard defines that at least 10 observation planes are mandatory, half of them within one Rayleigh length (zR), the other half beyond 2 Rayleigh lengths.

 

What are the limitations of traditional M2 analyzers?

 

– Limitations include the fact that the translation has to be aligned respect with laser beam propagation, which takes time and limits the throughput in production. This is particularly true if laser manufacturing requires iterative steps and M2 measurements.

– Beam caustics must also be adapted to the available range of the translation stage, in order to acquire observation planes in and out the Rayleigh lengths. This is done by carefully choosing lenses of appropriate focal. Such lenses bring added aberrations to measured beam depending on their intrinsic quality and, again, quality of alignment. In addition, lens coating must also match the spectral properties of the laser. Such implementation results in voluminous benches, whose length is sometimes contained by internally folding the laser beam several times with the use of multiple mirrors. These mirrors also represent additional optical elements external to the laser.

– Last, the complete acquisition cycle requires time to scan the -at least- ten positions defined by the ISO 11146 standard. Any variation of the laser during this time affects the reconstruction of the M2 factor, which limits their use in case of dynamics effects.

 

New approach to laser beam diagnostics proposed by Imagine Optic

 

Imagine Optic proposes a new approach to conventional M2 beam propagation analyzers: in this method, the complete electromagnetic field of the laser is acquired from a single shot measurement and, from it, allows to access to as many observation frames within and out the Rayleigh lengths defined by the ISO 11146 standard and to fit the parameter M2.

 

Advantages of the method

Laser beam diagnostics is performed by Imagine Optic CAM SQUARED sensor:

+ It allows fast live acquisition thanks to its single shot acquisition (us to ms), making it perfect for alignment and characterization of laser or OPA dynamic changes

+ It is easy to set up, like a beam profiler, because there is no need to use a translation stage anymore, nor to align it on the laser beam ( 40 Seconds Demo Video )

+ This makes it a compact solution, with small footprint in the lab or on the production bench, and easy to handle for after-sales support and on-site service.

Avoid the path of Kylo Ren and don’t let a bad M2 factor ruin your day when there are quick and easy solutions at hand to test the quality of your laser beam. We are happy to discuss how they suit your needs. Reach us at sales@imagine-optic.com or through the contact form.

Why is M2 factor important?

The parameter M2 or beam quality factor- describes laser beam quality, or how close it is from a perfect gaussian beam: in this case M2 will tend to 1 and correspond to a diffraction-limited beam. M2 factor therefore describe the ability a laser beam has to be perfectly focused, or collimated (greater values than 1 means the laser departs from an ideal gaussian beam).

As an example, a HeNe laser typically have M2 factor close to 1.1.

What is the Beam Parameter Product (BPP)?

The Beam Parameter Product is the product of the beam radius at the beam waist and beam divergence half-angle () measured in the far field. BPP can be used to inform on beam quality of a laser -the lower the BPP, the higher the beam quality- but it presents the disadvantage of being dependent of the wavelength.

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Shack-Hartmann wavefront sensor, constant improvement of the technology through innovation https://www.imagine-optic.com/shack-hartmann-wavefront-sensing-constant-improvement-of-the-technology-through-innovation/ Mon, 18 Dec 2023 16:06:12 +0000 https://www.imagine-optic.com/?p=266822 The post Shack-Hartmann wavefront sensor, constant improvement of the technology through innovation appeared first on Imagine Optic.

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 Shack-Hartmann wavefront sensor .

If Charles Darwin wasn’t thinking of the Shack-Hartmann wavefront sensor when he wrote his theory of evolution in 1838, it’s only because they hadn’t yet been invented. Since then, wavefront analysis technique has followed a steady evolution, accumulating inherited advantages combined with rapid adaptive leaps over almost a century, to become an optimum solution for modern optical metrology.

1900, 1st original idea by Hartmann

Around 1900, Johannes Franz Hartmann developed the Hartmann plate, consisting of an array of holes, which he used in combination with photographic plates to interpolate wavefront slopes and align telescopes.

 

1971, improvement by Shack (& Platt)

In 1971, Roland Shack and Ben Platt developed an optimized design for the Hartmann plate in which the array of holes is replaced by a much more efficient array of microlenses that concentrates light instead of widely blocking it, as with the mask.

Þ Combined with the advent of CCD cameras, this new approach has made the technique much faster, easier to use and adapted to “low light” applications such as astronomy.

Since then, the use of Shack-Hartmann sensors in optical metrology has continued to grow as they started to be used for laser testing, adaptive optics, ophthalmology for example.

 

1996, 1st commercial absolute wavefront measurement

Imagine Optic is established to materialize the vision of its cofounders: propose a reliable, easy to use and versatile tool for optical metrology at a time where only established alternative was the heavy, restrictive Fizeau interferometer.

Þ This is how the first Shack-Hartmann wavefront sensor offering live calibrated absolute measurement is commercialized as world premiere.

 

2001, first self-illuminated Shack-Hartmann

The LIP is born by combining our Shack-Hartmann wavefront sensor with an illumination feature in a built-in optomechanical platform.

Þ It optimizes optical quality and compactness of the solution in a ready to use to for transmission and reflection characterization of component.

 

2003, another patent

Imagine Optic turns the square apertures of the Hartmann plate, avoiding cross talk between adjacent sampling points.

Þ It allows to increase resolution and sampling of our HASO EUV Hartmann wavefront sensor operating at 248 nm.

 

2010, the advent of CMOS

Integration CMOS cameras as detectors for the wavefront sensors in replacement of the good old CCD.

Þ Customers benefit from faster and more sensitive sensors.

 

2015, broadband sensors

First Imagine Optic broadband Shack-Hartmann wavefront sensor offering absolute calibrated measurement in a wide 350-1100 nm spectral range with the HASO4 BROADBAND.

Þ Imagine Optic sensor precision of lambda/100 is now available for achromatic measurements at any wavelength

 

2017, instant setup feature

Invention of the SpotTracker  which avoid preliminary alignment procedure to make optical setup easier and quicker.

Þ It brings absolute tilt measurement and follow up over large variations unlike lateral shearing interferometers.

 

2020, resolution breakthrough

Imagine Optic moves/transposes and optimizes Onera’s experts research on LIFT technology to a commercial off-the-shelf solution

Þ Ultra High Resolution becomes available to Shack-Hartmann wavefront sensors with HASO LIFT 680 with a resolution of 680×504 phase points which is unheard of!

 

2022, an Optical Engineer Companion for the lab

 

Launch of the OEC : Imagine Optic makes its wavefront sensors, beam adapter modules, illumination platform, metrology sources interconnectable modules such as LEGO® bricks.

Þ It provides versatility to create any optical configuration needed for metrology: any beam size, any divergence, any wavelength, transmission and reflection.

Imagine Optic metrology solutions then combines in a flexible optical lab tool that adapt to projects over time and can be upgraded function of future needs.

 

These innovations are only here to make your metrology more accurate, robust and easier to use. Stay tuned for more info about Shack-Hartmann wavefront sensor.  We are happy to discuss how they suit your needs. Reach us at sales@imagine-optic.com or through the contact form.

What does a wavefront sensor do? What is the wavefront measurement?

 

A wavefront sensor measures the wavefront -a surface in which all the points have the same phase- of a light beam transmitted or reflected on an optical component (lens, windows, filter) or system (telescope, objective). The shape of the wavefront informs on the aberrations of the component or system and therefore on its optical quality and its performance.

What are the techniques used in wavefront sensing?

Apart from Interferometric methods, the wavefront can be measured by a large number of techniques, the most widespread of which is the Shack Hartmann wavefront sensing. Others include the Pyramid wavefront sensor, which can be assimilated to a scanning knife edge technique, Schlieren Imaging, a visual technique providing information on beam distortions, Wavefront Shearing Interferometry, a method measuring the slope of the wavefront such as Shack Hartmann wavefront sensing. Phase diversity uses a phase retrieval algorithm based on the analysis of intensity images and is declined in variants such as Curvature sensor and Generalized Phase Diversity sensors

How does a Shack Hartmann wavefront sensor work? What is the Hartmann shack method?

Operating principle of a Shack Hartmann wavefront sensor is very simple and compact, which makes them rugged:Shack-Hartmann Wavefront sensing Method

A Shack Hartmann wavefront sensor is made of two parts: an array of microlenses placed in front of a camera sensor. Each microlens samples the incoming optical beam by focusing a centroid on the detector. Analyzing the position of the centroids respect with their theoretical ideal position, one can calculate the slopes -or wavefront derivatives- as they correspond to the centroid displacement divided by the focal of the microlens.

What are the applications of a Shack Hartmann wavefront sensor?

Shack Hartmann wavefront sensors can be used for the characterization of optics, either in transmission or reflection, for the alignment of optical systems, taking advantage of the live feedback they provide, and to provide a signal to control the deformation of active components in adaptative optics and closed-loop systems.

Shack Hartmann wavefront sensors can be used in a wide range of application such as astronomy to measure telescopes or to correct atmospheric turbulences in free space optics; ophthalmology to characterize eyes for prescription, to guide lasik surgery or to control the correction of aberrations to better image retina in a variety of ocular diseases; microscopy, to control the correction of aberrations generated by thick samples; for laser beam diagnostic and collimation or measure broadband sources taking advantage that they can measure uncoherent light signal.

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Flatness measurement, when surface flatness gets critical… https://www.imagine-optic.com/flatness-measurement-when-surface-flatness-gets-critical/ Mon, 30 Oct 2023 11:13:44 +0000 https://www.imagine-optic.com/?p=266621 The post Flatness measurement, when surface flatness gets critical… appeared first on Imagine Optic.

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Flatness measurement. Sometimes surface flatness really matters… either you are trying to break speed record at Bonneville salt flats like Dave Spangler or producing flat substrates and mirrors for high demanding applications such as Mersen.

Boostec® Silicon Carbide SiC is an advanced ceramic material that has been designed for the most demanding applications in Space & Astronomy, Laser processes, Semiconductor or Opto-mechanics. As high performance comes with tight requirements, constant optical metrology control is of utmost importance to ensure these are met.

Imagine Optic offers solutions carefully designed for R&D, production optical lab and at line metrology environments and users.

Flatness Measurement

Flatness measurement of a polished SiC substrate measured with the OEC: surface figure error and Zernike coefficients are easily measured in real time.

Get a head start on your manufacturing process

The anufacturing process to obtain an optical quality surface counts many steps during which the part takes shape. In general, optical control can only take place at the end of this process, when the surface finish is eventually compatible with test instruments, such as Fizeau interferometers. 

 

Shift up a gear with metrology systems from Imagine Optic for surface flatness measurement: 

Flatness Measurement

MESO instrument allows customers to add any wavelength (up to 3) to the conventional 632.8 nm. By switching the test wavelength to 1064nm, it becomes possible to characterize not only polishing surface finish but also lapping surface finish! and thus, to test parts sooner in the process, improve its efficiency and speed up the whole fabrication process! 

 

3, 2, 1… GO!

Whether or not you race toward the latest equipment for your testing, we’ll be happy to discuss  what solution best suits your needs. Reach us at sales@imagine-optic.com or through the contact form.

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Celebrating Nobel Prize in Physics, again! https://www.imagine-optic.com/celebrating-nobel-prize-in-physics-again/ Wed, 04 Oct 2023 12:50:40 +0000 https://www.imagine-optic.com/?p=266537 The post Celebrating Nobel Prize in Physics, again! appeared first on Imagine Optic.

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Celebrating Nobel Prize: Pierre Agostini, Ferenc Krausz and Anne L’Huillier, Nobel Prize laureates in Physics 2023 for experimental methods that generate attosecond pulses of light for the study of electron dynamics in matter

Like every year, the award of the Nobel prizes is a highly anticipated event for the entire scientific community. This year, we are delighted to celebrate the Nobel Prize in Physics 2023, awarded to Pierre Agostini, Ferenc Krausz and Anne L’Huillier. We are particularly proud to have provided support with Philippe Zeitoun (LOA) to Anne L’Huillier, who has used Imagine Optic’s HASO EUV Hartmann wavefront sensor in her groundbreaking research.

Dr. Anne L’Huillier is a physicist working on the interaction between short and intense laser fields with atoms: extremely short light pulses of a few tens or hundreds of attoseconds in the extreme ultraviolet spectral range are used to generate high-order harmonics in gases. She has pushed the boundaries of attosecond source development and its applications such as the study of ultrafast electron dynamics.

For this field of research, our HASO EUV proved one more time to be an indispensable tool for the characterization, adjustment and alignment of such light sources as they provide single-shot, simultaneous detection of amplitude and phase, over a wide spectral range. Check our publication “Single-shot extreme-ultraviolet wavefront measurements of high-order harmonics”, DOI: 10.1364/OE.27.002656, co signed by G. Dovillaire, Imagine Optic CTO, for more insights on the potential of the wavefront sensor!  Celebrating Nobel Prize 

Since Imagine Optic was founded, we’ve been very proud to support the research and groups of several Nobel Prize winners over the years, to whom we’ve supplied adaptive optics solutions:

 + Stephan W. Hell and Eric Betzig, Nobel prize co-laureates in Chemistry 2014 for the development of super-resolved fluorescence microscopy (AO KIT BIO)

 + Gérard Mourou Nobel Prize co-laureate in Physics 2018 for their method of generating high-intensity, ultra-short optical pulses (HASO and ILAO STAR)

Congratulations to Dr. L’Huillier, Dr. Agostini and Dr. Krausz for the Nobel Prize in Physics 2023 and, through them, to the entire scientific research community. Their achievements inspire us to continue serving cutting-edge technologies for the betterment of science and humanity.

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Adaptive optics for Free Space Optics… and for fun! https://www.imagine-optic.com/adaptive-optics-for-free-space-optics-and-for-fun/ Fri, 21 Jul 2023 12:01:17 +0000 https://www.imagine-optic.com/?p=266293 The post Adaptive optics for Free Space Optics… and for fun! appeared first on Imagine Optic.

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Adaptive Optics Space Optics –
Incredible as it may seem, the famous reporter Tintin was already thinking, back in 1941 in L’étoile mystérieuse, Hergé, that telescope-based images could be greatly improved thanks to adaptive optics!

Adaptive optics for Free Space Optics (FSO) applications is a technique that couples a deformable mirror, a wavefront sensor and a calculator. Together, these components enable the wavefront of an incoming beam, and therefore its phase, to be modified very rapidly. Adaptive Optics (AO) has been developed in the 80s to remove the effect of air turbulences and get diffraction limited images from ground-based telescopes. Almost all large telescopes dedicated to high-resolution imaging have now an AO system. Imaging of exoplanets is the new goal for the new generation of AO system for astronomy.

AO is now used in many different applications such as:

Adaptive Optics for Ultra-High Intensity Laser: Imagine Optic ILAO STAR deformable mirrors are optimized for this application, where stability and large diameters are more important than speed. The deformable mirror removes residual static aberrations due to misalignment and thermal effects.

Adaptive Optics for Ophthalmology: Imagine Eyes RTX1 can acquire high-resolution images of the retina in vivo. AO is needed to remove all aberrations originating from the patient’s eye.

Adaptive Optics for Microscopy: Imagine Optic mu-DM deformable mirror has been designed to meet the specific needs of bio imaging (stability, dynamic, accuracy). Aberrations, particularly present when the focusing plane is deep in the sample, are compensated for to restore optimum resolution and signal intensity.

Adaptive optics Space Optics 

AO for high resolution imaging

 

A couple of years ago, a bunch of geeks (passionate amateur astronomers and AO experts) at Imagine Optic launched a project codename “CIAO” to validate they can build a simple, very easy-to-install setup, AO system capable of removing all static aberrations (mirrors misalignment, gravity and thermal effects) and reducing the effect of air turbulence in order to acquire better quality images.

What we got was a Plug & Play Adaptive Optics accessory with great performance at an incredible price point!

Imagine optic Adaptive Optics Passionate

Left: Some of us actually see the AO effect
Right: With a one-meter diameter telescope and no aberrations, we can reveal details of Mars that have never been seen from Earth

The CIAO Adaptive Optics System has now been tested on many kinds of telescopes (200mm up to 1.3m diameter, f/22 to f/8 aperture) to see how images are enhanced by this affordable system.
For instance, we were able to:

– see the Airy spot on a 1.3m diameter telescope with a seeing of 1.8 arcsec.
– prove that with a very bad seeing of 2.2 arcsec, a tip-tilt correction is surely not enough on a 355mm diameter telescope to get diffraction limited images as seen on image below:

Imagine Optic Adaptive Optics SFO

The effect of atmospheric refraction is clearly visible on the image obtained with AO

AO for single mode fiber injection | Adaptive Optics Space Optics 

CIAO efficiency has been evaluated for applications requiring the light received by a telescope to be injected into a single-mode fiber (Free Space Optics, satellite communication, Stellar interferometry, etc.). A first successful demonstration has already been conducted in the visible spectrum: we have proved that the coupling efficiency is improved and we have obtained an average flux level, at the fiber output, multiplied by a factor of 5. The second phase is now ongoing to establish the performance of a SWIR Adaptive Optics for Free Space Optics system, and the whole Imagine Optic team is fully committed to tackle the challenges of this new upgrade.

Left: AO OFF. Right: AO ON stabilizes the focal spot on the core of an optical fiber

Whether or not you consider yourself an AO geek, do not hesitate to contact us: we’ll be happy to discuss with you what adaptive optics solution for FSO best suits your needs …

 

Acknowledgments

Many people are involved in this work, all of them must be gratefully thanked: François Colas (IMCCE), Jean-Luc Dauvergne (S2P/Ciel & Espace, YouTube channel), Guillaume Blanchard (ESO), Pierre Guiot and Cateline Lantz (IAS), not forgetting the Imagine Optic teams.

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Optical characterization with a twist! https://www.imagine-optic.com/optical-characterization-with-a-twist/ Thu, 01 Jun 2023 12:44:05 +0000 https://www.imagine-optic.com/?p=266126 The post Optical characterization with a twist! appeared first on Imagine Optic.

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Optical Characterization – Spirals are ubiquitous in nature; why should laser beams be any different?

Orbital angular momentum (OAM) beams have attracted considerable interest in recent years due to their unique properties [1]: these beams possess a helical wavefront twisting around their propagation axis. This very specific characteristic encodes more degrees of freedom than classical beams and opens up new horizons in numerous applications with an incredible impact on our daily lives [2]:

> Optical communications > OAM beams offer increased information-carrying capacity and improved resistance to atmospheric turbulence, making them suitable for high-capacity optical communication systems with extended communication ranges.
> Quantum Information Processing > the OAM states of photons have been utilized to encode and transmit quantum information, contributing to the development of quantum communication protocols.
> Medical imaging and biophotonics > OAM beams can enhance the resolution and sensitivity of imaging techniques, enabling improved diagnostics and biomedical research.
> Optical manipulation > OAM beams have been used for optical trapping and tweezing of microscopic particles, enabling precise manipulation in biological and nanoscale systems. 

Over time, an extensive array of techniques has been developed to produce OAM beams [3]. Nevertheless, their comprehensive characterization continues to present several challenges. To fully utilize the numerous applications provided by OAM beams, it is essential to accurately determine their state. Consequently, suitable metrology and optical characterization techniques are mandatory.

But many of the commonly used methods for optically characterizing OAM beams either cannot retrieve their amplitude and phase simultaneously or require multi-shot acquisitions, which are susceptible to shot-to-shot fluctuations and strict beam stability requirements.

 

Wavefront sensing-based optical characterization

 

In contrast, Shack-Hartmann and Hartmann wavefront sensing methods solve these challenges, providing the opportunity for single-shot, simultaneous detection of amplitude and phase, over a wide spectral range from hard X-Rays (HASO HXR) to IR (HASO SWIR). This combined information is of the utmost importance as it enables more modes of OAM beams to be determined, which is crucial to exploiting their full potential.

Despite the emergence of various techniques for synthesizing OAM beams, their detection, especially in terms of single-shot amplitude, wavefront, and modal content characterization, is non-trivial. Imagine Optic’s wavefront-sensing solutions have demonstrated the ability for single-shot complete spatial amplitude and wavefront characterization of ultrashort OAM beams both:
in near-infrared [A. K. Pandey et al., Sensors 2022, 22, 132]
in extreme-ultraviolet (EUV) spectral range [A. K Pandey et al., Proc. SPIE 11886, International Conference on X-Ray Lasers 2020, 118860L].

Indeed, wavefront-sensing-based optical characterization of the spatial amplitude and phase has enabled retrieving the angular momentum spectra and complete modal composition for near-infrared and EUV helical beams [F. Sanson, A. K. Pandey, et al., Opt. Lett. 45, 4790-4793, 2020] exhibiting extremely high topological charge [A. K. Pandey et al., ACS Photonics 2022, 9, 3, 944–951; A. K. Pandey et al., Eur. Phys. J. Spec. Top. (2022)].

simulatneous_phase_intensity

Left: single-shot intensity map of femtosecond EUV vortex beam characterized using Imagine Optic’s HASO EUV. Right: single-shot characterization of the twisted helical wavefront of femtosecond near-infrared vortex light using Imagine Optic’s HASO4 FIRST.

One step further

It is possible to push further the optical characterization with Imagine Optic’s HASO Multispectral, the first-ever spectrally-resolved wavefront sensor, which allows wavefront measurements in the 550 – 1000 nm spectral range with a spectral resolution of 1nm [in Laser Congress 2019 (ASSL, LAC, LS&C), OSA Technical Digest 2019, paper JM5A.30]. Leveraging this ability, the HASO Multispectral opens the possibility of spectrally-resolved complete spatial characterization of the broadband OAM beams, even in the few-cycle regime.

Imagine Optic wavefront sensors represent a commercially available, turnkey metrology solution which avoids customers having to design and maintain complex setups and lets them focus on the science.

Whether or not you’re looking for spirals anywhere in nature, we’ll be happy to discuss with you what solution best suits your needs. We have suitable tools and expertise in OAM beam metrology, Fabrice Sanson, Ph.D. and Alok Kumar Pandey, Ph.D in optical characterization. Reach us at contact@imagine-optic.com.

References

[1] Adv. Opt. Photon., 3(2):161–204, 2011
[2] Light Sci. Appl. 8(1):90, 2019; Photon. News, 31(6):24–31, 2020; J. Phys. Photonics 3, 022007, 2021
[3] Nanophotonics 7, 1533–1556, 2018; Light Sci. Appl. 8(1):90, 2019

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Plane optics quality control https://www.imagine-optic.com/plane-optics-quality-control/ Thu, 11 May 2023 12:47:06 +0000 https://www.imagine-optic.com/?p=266101 The post Plane optics quality control appeared first on Imagine Optic.

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plane optics quality control

NIGHTMARE, a rather average 1981 horror movie that yet perfectly recreates the TERROR of an optician confronted with a reflection on the back surface of a sample under test

Windows, prisms, filters, mirrors, crystals…from the (so) precious and fragile thin screens of our cell phones to the large tough airborne pod windows, plane-parallel optics are omnipresent in our daily life and professional applications.

It is therefore no surprising that the optical metrology of these components is of the utmost importance. It is more surprising, however, that the testing of such components, with no power, no complicated shape requiring huge dynamic range such as aspheric or freeform optics, can result in a tricky use case if not a NIGHTMARE. Isn’t it?

That’s why plane optics has been the subject of much effort, frustration, additional costs and technical patches for many years. We reviewed some of them in this white paper [Link to the white paper]. In this blog post, we propose to tell the story of how our production technicians stopped having BAD DREAMS and COLD SWEAT when it comes to characterizing and validating thin plane-parallel optics (glass substrate) before we mount them.

plane optics quality control

Unwanted interference, the TERROR of optical testing

 

When it comes to perform the metrology of plane optics, it might happen that you get multiple reflections from your sample under test:

– for example, you need to deliver a control sheet to your customer together with the nice protective windows you just produced. Bad news for you, it’s an AR coated, both surfaces are parallel and reflect the same amount of signal back to your instrument, with no way to filter one from another.

– lucky you, you need to characterize a coated mirror, with excellent reflectance at 1030 nm. Sadly, your metrology tool is based on a HeNe laser at 633.8 nm, where the AR coating is no longer reflective: you then get a GHOST signal from the back reflection of your mirror that disturbs the one you are interested in.

plane optics quality control

WAKE UP: the Parallel Optics Procedure (POP) will chase away your BAD DREAMS!

 

At Imagine Optic, we sell metrology solutions and we are also the first ones to need and use them: that’s one of our motivations to develop and perfect them.

In particular, we need to test the optical quality of glass substrate we implement in our products, custom metrology benches: dichroic, filters, beam splitters, windows, as surface shape and mid-spatial-frequency errors could impact the final performance of the systems.

To this end, we use a proprietary (patented) technique, POP -standing for Parallel Optics Procedure-, that allows for the characterization of large thin plane-parallel optics in two simple steps:

– step 1 > measurement in reflection on the glass substrate: our instrument MESO acquires the combined aberrations of the test beam reflected by the front and back surfaces of the sample

– step 2 > measurement in transmission on the glass substrate: MESO gets the transmitted aberrations of the sample as the test beam pass through the front and back surfaces (in double pass).

From these two measurements, it is possible to retrieve the surface figure error of both surfaces:

Plane optics SFE

Surface Figure Error (SFE) of the front surface (left column) and back surface (right column) of a 200 mm glass substrate characterized before coating with POP, Imagine Optic proprietary Parallel Optics Procedure

Conveniently, the user also obtains the transmitted wavefront error (TWE) as a bonus, with no extra effort! If we filter the low-order aberrations, we can even identify the pattern generated by the polishing tool, as shown in picture below:

plane optics TWE

Transmitted Wavefront Error (TWE) of the same 200 mm glass substrate characterized before coating with POP, Imagine Optic proprietary Parallel Optics Procedure

Whether or not THERE IS A MONSTER IN YOUR CLOSET, we’ll be happy to discuss with you what solution best suits your needs. Reach us at contact@imagine-optic.com  .

 

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Interferometry and wavefront sensing: the best of enemies? https://www.imagine-optic.com/interferometry-and-wavefront-sensing/ Thu, 23 Feb 2023 15:56:38 +0000 https://www.imagine-optic.com/?p=265845 The post Interferometry and wavefront sensing: the best of enemies? appeared first on Imagine Optic.

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Interferometry and wavefront sensing Illustration: Roger Federer, 20 Grand Slams and Rafa Nadal, 22 Grand Slams still counting

Tom and Jerry, Roger Federer and Rafa Nadal, Peter Pan and Captain Hook, some would say France and England, history is full of ‘meilleurs ennemis’. Could it be that Interferometry and Wavefront Sensing fall in this historical category?

Interferometry has long been adopted as a reference in optical metrology. Generation of interference is as old as optics and its use is therefore well known and widespread. Fringe interference pattern, this pattern of dark and bright stripes is directly linked to the wavelength, which has the good taste of being small in the case of light waves, and therefore represents a very good indicator of small defects of surface shape and flatness or transmitted wavefront.

Wavefront sensing -which refers to the act of measuring aberrations with sensors that do not require an unaberrated reference beam to interfere with- is slightly newer. Although it is easy to argue that it may already have a similar capillary age to Rafa… Shack-Hartmann Wavefront Sensors measure wavefront derivatives by sampling with an array of lenslets and measuring the displacement of centroids they focus on a 2D photon sensor (typically a CMOS camera). Their accuracy is no longer contested and their use in optical metrology, optical system alignment or adaptive optics correction is generalized.

 

So, what is the current status of the two techniques?

Well, there is no question that interferometry is a standard. Any optical manufacturer will have a Fizeau interferometer or a Twyman-Green interferometer for quality control. However, in some situations, they might not be the best fit. This is precisely where Shack Hartmann wavefront sensors and their new brothers the high resolution LIFT sensors represent a winning alternative.

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When it comes to measuring in the presence of vibrations or atmospheric turbulences, metrology solutions based on Shack-Hartmann or LIFT principle are easily implemented on the shop floor with no need of additional, bulky and expensive equipment.

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If it comes in handy to measure at specific wavelengths, with Shack Hartmann wavefront sensors it is easy to get away from the typical interferometer’s HeNe laser and accommodate with the specificity of the coating -or material- of the optics to be tested.

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For situations where reflections from the back surface of optics creates unwanted interference, Imagine Optic’s patent for (thin) plane parallel optics characterization offers an alternative to the preparation of the substrate with in-house secret recipe coatings. Browse our website to learn more about interferometry and wavefront sensing. Browse our website to learn more about interferometry and wavefront sensing 

 

Like Rafa Nadal and Roger Federer, both Shack-Hartmann wavefront sensors and Fizeau interferometers have their own field of choice.

Whether or not you enjoy tennis or historical rivalries, we’ll be happy to discuss with you what solution best suits your needs.

Reach us at sales@imagine-optic.com or through the contact form.

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Nanolite, a CEA-Imagine Optic joint lab on Extreme UV metrology https://www.imagine-optic.com/nanolite-extreme-uv-metrology/ Tue, 06 Dec 2022 13:38:05 +0000 https://www.imagine-optic.com/?p=265385 The post Nanolite, a CEA-Imagine Optic joint lab on Extreme UV metrology appeared first on Imagine Optic.

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 Extreme UV metrology joint Lab, Nanlite , Imagine Optic – CEA

NANOLITE, the novel optical metrology platform for extreme UV enters operational phase.

Nanolite, established January 2020, is a joint collaboration and laboratory between the LIDYL CEA laboratory (CEA-CNRS) and Imagine Optic, focusing on innovative optical metrology and imaging solutions at short wavelengths, in particular in the Extreme-UV (EUV, typically between 10 and 100nm) range. Along the Nanolite roadmap, a major milestone is the availability of a novel EUV source providing large photon flux, high stability and beam quality, based on the use of an original laser source. This first milestone has recently been successfully passed.

This high-performance beamline will now serve as a key device to advance the next Nanolite objectives. On top of being an ultra-precise calibration source for current EUV wavefront sensors and future developments, it will enable the development of “at lambda” metrology solutions, in particular for the qualification of X-EUV optics. Such optics, e.g. used in Synchrotron beamlines, ideally require accurate quality control before installation, which is currently not possible with the required level of precision when based on measurements in the visible range. At lambda wavefront sensing in a context approaching its final working conditions will provide both increased accuracy and more relevant results. Moreover, the source will also contribute to the next developments on ultrafast nanometric imaging mainly driven by LIDYL, with applications focused on the study of ultrafast magnetization – a possible key tool to drive the electronics of the future.

By providing their expertise in the characterization and the generation of “made-to-measure wavefronts” Imagine Optic is happy to contribute to the definition of novel metrology solutions in the short wavelengths, on top of our current range of wavefront sensors such as HASO-EUV or HASO HXR

 

 

Read the full announcement by CEA hereunder (French only).

 

 

 

 

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