Recently, Boston Micromachines sponsored MiFoBio (Functional Microscopy in Biology), an event that brought together the microscopy community, academics and professionals alike, to attend courses and workshops that explored the understanding and current trends of biological imaging. Held in Seignosse, France from Oct 5 to 12, 2018, a Boston Micromachines Kilo-S-SLM deformable mirror was utilized in a microscopy demonstration of imaging through scattering media shown to the participants at the workshops.
Images courtesy of MiFoBio.
Thanks to Sylvain Gigan, Baptiste Blochet, Sophie Brasselet and the team at Laboratoir Kastler Brossel for the invitation and continued support of our deformable mirror technology!
Dr. Meng Cui at the Howard Hughes Medical Center has recently pioneered Super Penetration Multi-Photon Microscopy (S-MPM) at the Cui Lab. He has successfully reported on focusing light through static and dynamic strongly scattering media using our segmented 492-DM (See more on the application here). By using the iterative multi-photon adaptive compensation technique (IMPACT), he since reported new results on in vivo fluorescence microscopy, providing a unique solution to noninvasive brain imaging. I HIGHLY encourage everyone to read his paper for in depth details of his technique here.
As of today, IMPACT has been the only technique used for in vivo microscopy. Due to the complicated wavefront distortion encountered in highly scattering biological tissue, IMPACT has the highest success rate in enabling neuron imaging through intact skulls of adult mice. Through Dr. Cui's testing, he has proven that even with the unpredictable motion of awake mice, IMPACT using the segmented 492-DM were able to perform wavefront measurements and improve the image quality.
Dr. Cui used the BMC segmented 492-DM as both the wavefront modulation and correction device. The IMPACT measurement works by splitting the DM’s pixels and running parallel phase modulation with each actuator at a unique frequency. Modulating only a portion of the pixels while keeping the rest stationary, a linear phase shift is then used as a function of time over the entire 2π phase range. The unique modulation frequency then becomes the unique phase slope value. At the end of the modulation, a Fourier transform is used in IMPACT to determine the correction phase values. Dr. Cui then goes on to explain in detail how to determine what fraction of the pixels should be modulated, how to split the pixels into two evenly distributed groups and how the Nyquist-Shannon sampling theorem is integrated.
The imaging starts by setting the laser beam at the point of interest. The parallel phase modulation begins at one half at a time. As the measurement progresses, the laser focus becomes stronger, and laser power is gradually reduced to preserve the fluorescence signal from the sample. At the conclusion of the measurement, the compensated wavefront is displayed on the DM, and laser scanning in a conventional scope is begun. Figure 1 below shows the test setup for the experiment.
Figure 1. Setup of the multiphoton microscope integrated with IMPACT.
Dr. Cui used IMPACT for imaging the dendrites and spines of layer 5 pyramidal cells, in vivo at 650-670um under the dura in the mouse S1 cortex. In Media 1 below, you can see they are hardly resolvable with system correction only. In Media 2, you can see the dendrites and spines are clearly determined when full compensation has been applied.
Media 1. Hardly resovable dendrites and spines Media 2. Resolved dendrites and spines
For the first time, IMPACT enabled in vivo two-photon fluorescence imaging through the intact skull of adult mice. The technique also improved the fluorescence signal by a factor of ~20, along with overall resolution and contrast, this has proven to be a much greater adaptive optics imaging method than any other before. Dr. Cui also concluded that through these experiments, he found it worked well for awake, head-restrained animal imaging, providing a new and innovative solution for noninvasive studies of the mouse brain.
For more information on research going on at the Cui Lab, click here.
If you are interested in finding out more information on how the segmented 492-DM can help you achieve fluorescent imaging, please contact us here!
Before Deformable Mirrors became popular in the Adaptive Optics industry, consumers would generally turn to liquid crystal-based device (LCOS) spatial light modulators to confront their challenges. Here at BMC, we regularly receive questions on how all deformable mirrors, in addition to our MicroElectroMechanical (MEMS) deformable mirrors, compare to LCOS devices. Below I have touched upon some of the top differences between the two devices that I believe should play an important factor in one’s decision to purchase a wavefront shaping device.
1) LCOS devices are only available in a segmented architecture, where MEMS DMs offer both continuous and segmented styles in various styles and options. Although both layouts have their own advantages, most researchers favor the continuous model. Due to discontinuities between the actuators, it prevents any sharp edges within the image, making it well suited for imaging applications. Claire Max at UC Santa Cruz has explained and presented calculations on how you can achieve higher level of correction capability with a continuous mirror. Check out slide 47, which goes over her calculations here.
2) With MEMS DMs, we are able to offer strokes up to 5.5um (1.5um, 3.5um and 5.5um available), while LCOS SLMs are generally limited to only a stroke of 2PI in the visible region. This can be a major inconvenience for certain applications with higher amplitude aberrations.
3) The response time of our devices have always been much faster than any liquid crystal device on the market, while recent updates to our product line achieve even FASTER rates than before. Our devices can operate up to 60 kHz with our new high speed Kilo-S Driver or our Low-Latency Driver, whereas LCOS devices are limited to only a few hundred Hertz at best.
4) For the most part, LCOS devices are transmission based, causing light to be absorbed by the medium and resulting in lost light. There have been reflective devices introduced recently, however, they tend to scatter large amounts of light due to the small segment sizes. With a MEMS device, our segmented mirrors are over 98% reflective and our continuous mirrors are greater than 99%. Of course, this is the case only with the appropriate coating for the wavelength at which you are operating.
If you're interested in learning more about the differences between MEMS DMs and LCOS devices or the differences between any other mirrors currently on the market, please feel free to contact us here.
Scattering media can be a real headache if you are looking to achieve high-resolution, deep tissue in vivo images. Without adaptive optics, do not anticipate having the optical control you need to correct for scattering media effectively. But no need to worry, we have a solution.
Since standard Multiphoton Microscopy just wasn’t cutting it, the Cui Lab at Howard Hughes Medical Center pioneered a new technique that Boston University also recently developed, called Superpentation Multi-Photon Microscopy (S-MPM). Each group uses a different optimization scheme but the outcome is the same: The enhanced technique permits active compensation of wavefront aberrations in a scanning beam path through the use of a BMC MEMS Spatial Light Modulator (SLM), allowing for increased depth imaging.
Developed at Boston University and commercialized by Boston Micromachines, the enabling components are the Kilo-SLM and the high speed S-driver. With these components incorporated into the test bed shown in Fig. 1, images of 1 µm diameter fluorescent beads through 280 µm thick mouse skull can be achieved at depths of about 500 µm. The SLM corrected low order spherical aberrations as well as higher order scattering effects. Signal enhancement with higher resolution and contrast were improved by 10x-100x. The optimized SLM phase improves imaging over a field of view of 10-20 µm for samples tested to date with techniques currently in the works to improve upon this.
With 600 nm of stroke and 60 kHz of maximum frame rate, the Kilo-S System comes in a variety of options to fit your needs at a much reduced cost over our standard 1000 channel system. Contact us today for more information on our Kilo-S or any of our other systems!
Just a few weeks ago we arrived back from the Photonics West 2014 exhibition and conference in San Francisco, CA. I wanted to share details and further observations on the show for those present at the show and those not being able to attend this year.
For the first time we made the decision to also attend the BiOS exhibition for the few days prior to PWest. Not being quite sure what to expect for booth traffic, especially since it conflicted with the superbowl, we still generated a good amount of interest for the smaller show. Our main presentations focused on our new adaptive optics-enhanced scanning laser ophthamoscope (AOSLO), the Apaeros Retinal Imaging System, which includes our Multi-DM, and the Superpenetration Multiphoton Microscopy technique, which is enabled by our Kilo-SLMand high speed S-Driver. Although both exhibits generated respectable notice and positive feedback, most people were familiar with the Superpentration Multiphoton work being done. Either wanting to try two-photon microscopy themselves or already in the process of doing so, our Kilo-SLM paired with our high speed S-driver presented data that was intriguing to most.
After wrapping up BiOS, we headed to the opposite side of the South hall at the Moscone Center for a larger booth setup for PWest. Here we had our entire mirror family on display, as well as live demonstrations of theReflective Optical Chopper and Wavefront Sensorless Adaptive Optics Demonstrator for Beam Shaping (WSAOD-B). For this part of the exhibition, I would say our deformable mirrors produced the most attention, most likely due to our wide assortment of shapes and actuator counts up to 4092. The WSAOD-B live demonstration did generate a great deal of attention, as most people are unaware of how sensorless AO works. Besides our deformable mirror line, I would still say the Multiphoton Microscopy overview was initiating even further interest here as well.
Overall BMC had a great show and it seemed well worth it to expand our exhibit onto BiOS beforehand. Although this was my first time attending the show, I noticed every inch of space at PWest being used for exhibitor tables and booths, even setting up in front of the bathrooms! I hope to see PWest advance even larger, maybe one day expanding to its third space, West Hall. I look forward to next year’s show and hope to reconnect with you all again throughout the year.
If you were not able to attend the show and would like any information on the products mentioned, please visit our websiteand download our whitepapers.
In our second installment of this series designed to boil down the questions that need to be answered before selecting the right mirror, we will review some of the past categories with alterations specific to laser beam shaping and introduce a few new ones that pertain only to beam shaping. We plan to focus on pulse shaping applications in our third and final installment of this series.
So you have a beam (CW or pulsed) and you want to control it. Below are the fundamental questions that need to be asked in order to ensure that you’re on the path to obtaining great results in your research or manufacturing application. This list should be combined with Part 1 of this series to get the total picture of what’s needed. I have left out the “pitch” and “response” categories, assuming that you have read the previous installment. Click here, in case you haven’t.
1) Aperture: How big is your beam?
The size of the wavefront is the first and foremost issue to understand. Some applications have no control over this while others can change the size of their wavefront through the use of some simple focusing optics. Before doing research into your alternatives, you should figure out what your limitations are in relation to this.
2) Control: Phase control? Beam steering?
This will greatly affect the basic type of mirror you will need. For phase control, most modern phase-only mirrors will work, depending on your requirement of resolution (see “2. Resolution” from Part 1 of this series). However, if you get into beam steering, the amount you need to move your beam will greatly affect the type of mirror you need. For example, if you’re trying to move the beam multiple degrees, a fast-steering mirror is probably a good place to start. However, if you’re looking to only make very fine adjustments (milliradians), you can benefit from MEMS-based solutions which are usually referred to as tip-tilt-piston (TTP) devices or piston-tip-tilt, if you’re from one other particular company out there (you know who you are J). Many customers have come to us asking about using our entire mirror surface to steer a beam. For those asking for big angles, we unfortunately have to turn them away, but some want to steer it a very slight angle at high levels of precision and we can do that.
3) Speed: Do you want to make fine adjustments? Are you looking to phase-wrap?
If you’re shaping a beam that is pretty much static, then some low-cost solutions will work. However, if you’re looking to change the profile at high speeds with high precision, MEMS solutions are a great bet. The stroke is sufficient to accomplish phase-wrapping, using our SLM model (segmented surface). With sub-nanometer precision, very precisely-shaped beams are possible.
This is a biggie: If you have a high-powered laser, your options become limited very quickly as most of the very precise devices are a bit fragile as well. Lots of research is being conducted to steer big, powerful lasers and the bulk of the technologies out there fall short due the fact that they are made of thin-film surfaces and temperature-sensitive materials. My recommendation for this is to make sure you know the “big three” properties and contact individual manufacturers to see what their experience is. They are:
1) Peak power (in W/cm2)
2) Average power
3) Pulse width (if applicable)
Most manufacturers probably can’t guarantee much, but if your application has beam characteristics close to some of the data points they have, then it will make you much more comfortable that you won’t be frying mirrors when you fire things up. BMC has a database that is constantly being updated with new experience that we would be happy to discuss. Also, see this paper for the latest published results from our friends at the UCO/Lick Observatory.
As I mentioned before, this is not exhaustive, but if you have these questions answered, your first conversation with either us or one of our competitors will be a pleasant one which will make you more confident of your purchase.
Please chime in and let me know what you think of this series! Again, stay tuned for the final installment where I will talk about pulse-shaping and the different ways that deformable mirror technologies can be used to create the perfect pulse!
Michael Feinberg is the Vice President of Marketing at Boston Micromachines Corporation. He has over 10 years of marketing and engineering experience in various technology fields. He can be reached at firstname.lastname@example.org and welcomes any comments about the content presented herein.