Tags: deformable mirror, adaptive optics, boston micromachines, resolution, segmented, SLM, spatial light modulator, biological imaging, deep tissue microscopy, Howard Hughes Medical Institute, Janelia Farm Research Campus, BMC, imaging systems, microscopy, two photon, fluorescence
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!
Tags: deformable mirror, adaptive optics, boston micromachines, product information, response time, segmented, SLM, spatial light modulator, mirror technology, BMC, speed, Reflectivity
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.
Tags: deformable mirror, adaptive optics, boston micromachines, retinal imaging, free-space communication, modulating retroreflector, segmented, laser beam, SLM, spatial light modulator, deep tissue microscopy, SPIE, BMC, imaging systems, Photonics West, microscopy, two photon, optical chopper, optical modulator, chopper, Adaptive Optics Scanning Laser Ohphthalmoscope, Joslin Diabetes Center, Mirrors
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-SLM and 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 the Reflective 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 website and download our whitepapers.
Boston Micromachines has been awarded US$ 1.2M in contracts by NASA's Small Business Innovation Research Program (SBIR) to support space-based astronomy research. Now, one might wonder, considering this is astronomy, “why is anyone spending any money to develop deformable mirrors for use in space telescopes looking out at the stars? I thought that deformable mirrors were used to remove aberrations introduced by the atmosphere. There’s no atmosphere up there!”
Well, you’d be right: There is no atmosphere up there. But, there are aberrations: In the optical system. When systems are designed, none of them are completely perfectly aligned. There’s no such thing. But, when you’re looking for planets around stars in other galaxies, you need things to be well aligned. VERY well aligned. So, to compensate for any misalignments introduced either during transit to space or thermal variations in the instrument, you can use a deformable mirror as part of an adaptive optics system. So, for this, we are designing a 1021 segment (3063 actuator), tip-tilt-piston deformable mirror. It is the largest ever designed of this type and is expected to be used as part of a coronagraph telescope for exo-planet research.
Two other things to worry about are power and weight. In satellites, there is a very limited amount of power, and the weight greatly affects the cost to put the satellite into orbit. In terms of the mirror, MEMS has that taken care of: The power is extremely low and the weight is many orders of magnitude lower than traditional piezo-electric-based mirrors. So, the other half of the equation is the drive electronics. As part of this research, BMC is designing multiplexed drive electronics which will reduce the size and weight significantly and lower the power even further.
You put the two parts together, mirror hardware and drive electronics, and you have a low-cost, low-power, lightweight solution for the most cutting edge astronomy research going on right now.
If you have any questions, please contact me directly: I would be happy to talk about these products or refer you to the folks who are attacking this challenging problem.
Link to press release.
(Image credit: A giant Hubble mosaic of the Crab Nebula, a supernova remnant)
Although William Wallace shouted this in the movie, “Braveheart,” as he died in the hopes to inspire others to join his fight against tyranny, our interest here at Boston Micromachines is related to “degrees of freedom” rather than individual rights. I chose this as a post because numerous times we have come across customers who miscalculate the minimum number of control points (re: actuators) needed to satisfy their wavefront control needs because the forget about this simple concept. Here’s an example:
A customer recently came to us insisting that they needed one of our advanced tip-tilt-piston devices over a continuous surface deformable mirror. Their reasoning was that with the same number of actuators, to correct for their wavefront, tipping and tilting the individual segments would give them more control than using the simple piston mechanism of our continuous device. This is true if you compare the number of segments (with three actuators) to the number of single actuators of a continuous DM. However, if you choose to use a tip-tilt-piston device over a continuous surface mirror, you actually need more actuators (if you work out the numbers, 1.8 times more) to achieve the same level of correction capability. This has been explained and presented very well by Claire Max at UC Santa Cruz. See the presentation materials here (Slide 47 goes over the equations).
If we step back from the equations and look for the basic concept behind this, it boils down to the ability to change the profile of the surface in many more ways using a continuous membrane as opposed to stiff, separate segments. Even more simply put: If you want to approximate a curvy line using only a few points (five, let’s say), would you prefer to use a slightly less curvy line, or a series of straight lines?
The figure below illustrates this concept.
So, the next time you’re considering wavefront control, keep this in mind before hitching your wagon to a particular architecture. THINK FREEDOM!!!!!