Ajou University in Korea has recently reported on femtosecond scanning photocurrent microscopy using our Optical Modulator devices. In this application Ti:Sapphire lasers were divided into pump and probe beams, then focused on the samples using an objective lens, while a pair of two-axis steering mirrors were used to manipulate the positions of both focused laser spots. Our optical modulator was then used to modulate the probe pulse at 20 kHz to capture the photocurrent generated by the probe pulse signals and filter out the photocurrents generated directly by the pump pulse. It is noted in their paper that “this modulator is advantageous over the acousto-optic types because it is free from the dispersion effects and delivers better spatial resolution for the focused laser”. Figure 1 shows the setup of the experiment.
Figure 1. Schematic of experiments. (a) Schematic diagram of ultrafast carrier dynamics in a semiconductor nanowire device. (b) Schematic diagram of the experimental setup (CM, chirped mirrors; DM, optical modulator).
For the results on combining scanning photocurrent microscopy and ultrafast pump probe techniques, head to ACS Nano to read the full paper.
If you would like further information on BMC's Optical Modulator technology and the Reflective Optical Chopper, which includes a high-speed driver for the Optical Modulator, please contact us here.
About half of our customers use our deformable mirrors for laser applications, such as beam shaping or steering. We get a lot of questions pertaining to laser power and handling for both our deformable mirrors and modulators. Below is a summary of the guidelines we use when discussing our technolgy.
The most important specification to note immediately if you are working with lasers is the damage threshold of our DM's. There are two mechanisms of failure to consider: mirror damage due to heating and coating delamination. The first failure mode is largely governed by the average power experienced by the DM. The rule of thumb that we follow is maximum average power of 20W/cm². For the second failure mode, the peak energy is of greatest concern. In this case, the threshold that we use is that of a standard thin-film gold metallic coating, in this case, 0.4J/cm². Depending on the DM system, the calculations may be slightly different. In order to ensure a DM is suitable for your application, we typically need to know as many of the following properties as possible: the pulse width of the laser, peak power, frequency, wavelength and beam size. This last pameter will help to determine which aperture size is required and if you need to change your beam size at all. Additional information on laser power can be found on our previous blog here.
From a power threshold standpoint, our modulator technology works similarly to our deformable mirror technology. However, it may have a slightly lower damage threshold due to the fact that the exposed surface is a thin layer of silicon nitride as opposed to the thicker polysilicon surface used for our deformable mirrors. Honestly, we do not have much experience testing the devices. If you are interested in carrying out testing, we would be glad to lend you some modulators to test.
If you are interested in learning more about customers' experience with high-power lasers used on our DM's, pleaseclickhere to read Andrew Norton's paper on laser test performed using our DMs. Also, please visit ourwebsiteor contact usfor questions or additional information on how to obtain a device for testing.
For those interested in using our deformable mirrors with laser applications, there are a few common questions which are asked in regards to the AR-coated window and if it is/can be removable. Below is a summary of what's standard and what's possible:
Both the optical modulator and our DMs are protected by a 3mm thick window, which are standard BK-7 windows fromThorlabs. The options for windows are:
This can also be customized upon request. The windows are mounted on a 6° angle in order to prevent ghosting.
A lot of requests are in regards to removing the protective window. For our standard DMs, the window is not removable as it is attached with an epoxy. For our modulators, the windowIS removable. We highly recommend youDO NOT REMOVE the protective window. The only exception to not having an AR-coated window would be if the DM was operated in a clean room environment. In this case, we can deliver the modulator or DM without the window and include a protective removable lid instead. In addition, we recommend flowing Nitrogen at a very slow pace around the mirror to ensure the humidity remains low around the DM. The required humidity is <30% as the mirror is made of polysilicon which needs to be protected from corrosion.
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.
It's been a few weeks since we returned from the Conference on Lasers and Electro-Optics 2013 and now that we're settled back in to the daily routine, I thought I would give some highlights on the show. I was happy to be joined this time by our new Marketing and Communications Specialist, Angelica Perrone, who did a great job navigating the complex photonics market for the first time.
While the conference seems to be chugging along at a nice pace, the tradeshow has most definitely become a smaller venue. We were once again hosted by our strategic partner, Thorlabs (thanks, again guys!) and being in such a central location on the floor, we were able to get a good flavor for the pace of the show. Here are my thoughts:
Little, different, yellow, better
Anybody get that Nuprin reference? Anybody? See what I 'm talking about here.
Okay, so it's not yellow (although yellow lasers are cool), but the show is definitely getting smaller. I mentioned to a colleague that since the show is in San Jose for the second year in the row, it seemed like the barriers on either end of the tradeshow floor had moved in just a bit.
As far as different, the show is not like other photonics shows in that it is pretty focused in its applications. While there were some interesting talks on microscopy, this was a small portion of the material, with most others focussing on more laser-centric applications, as the title of the conference implies.
As far as better, I would say that for BMC, it was most definitely better for our new products: The Reflective Optical Chopper(ROC) and the Linear Array DM. We recieved more interest in these products over our legacy deformable mirror technologies. This is exciting for me as a product marketer and salesperson and even moreso as a member of a company that is always looking for new avenues for our technology. We see the ROC being useful for users who span from pure laser scientists to imaging engineers interested in chopping a beam at high speed with either a constant or variable duty cycle. The linear array has already proven useful in pulse shaping applications as described in our whitepaper, which is available for download here. Both products are available for purchase now.
Our Wavefront Sensorless Adaptive Optics Demonstrator for Beam Shaping (WSAOD-B)also generated some buzz. More and more applications which require wavefront correction are surfacing and need a solution without a wavefront sensor.
In all, it was a good show that has given me and my team work to do as we explore more exotic applications for our technology. I look forward to joining the show again next year and I hope to connect with all of you again in the near future!
For more information on the products mentioned above, please visit our website and download our whitepapers.
Up until recently nearly all adaptive optics (AO) systems used wavefront sensors for correction. But with recent advances, off-the-shelf wavefront sensorless AO is becoming a reality. Benefits of this type of AO include enhanced aberration correction due to the elimination of non-common path errors and wavefront sensor noise.
BMC has developed a Wavefront Sensorless AO Demonstrator (WS-AOD) which provides a platform for utilizing metric-based wavefront control with BMC MEMS deformable mirror (DM) technology. While conventional AO systems perform closed-loop DM control using direct measurements of the wavefront as feedback, the metric-based approach uses details in the aberrated light to improve clarity. Two versions are available; one is optimized for beam shaping applications and the other is designed for imaging applications.
We see laser beam shaping as a key area in this exciting technology and our demonstrator is built to address the unique challenges of this field. Our WS-AOD serves as an introduction to wavefront sensorless adaptive optics principles. It allows users to understand the details involved in properly implementing a metric-based adaptive optics solution on an optical system. The demonstrator can also be used as a stand-alone aberration compensator. By introducing aberrations in the sample stage, the system can be optimized for a multitude of use cases from laser research applications to scanning laser microscopy. Additionally, the user can easily integrate the hardware into an existing optical system and utilize the open source software code for metric-based correction.
Schematic of WS-AOD for beam shaping applications. Also available for imaging applications.
To compensate for phase aberrations the WS-AOD uses BMC’s deformable mirror (DM) technology. BMC’s DM is a continuous facesheet deformable mirror that is controlled by hysteresis-free electrostatic actuators located on a square grid. The full DM active aperture can be as little as 1.5 mm to as much as 25 mm across. Each actuator can provide up to 5.5 µm of mechanical stroke, which corresponds to about 11 µm of phase control. The electrostatic actuator array is driven using independent high voltage channels with 14-bit resolution. This corresponds to sub-nanometer displacement precision. The drive electronics can provide frame rates of from about 4.6 kHz up to 100 kHz.
The control software for WS-AOD allows the user to correct for aberrations introduced as well as generate a random aberration using the DM. The software is open source code based in Mathwork’s Matlab and runs on platforms using Windows operating systems. By utilizing the included algorithm to manipulate the mirror surface, the mirror compensates for aberrations and converges to an optimal profile. The user has access to the open source code to balance correction capability between maximum signal and minimal time.
To learn more please click here for a copy of our Wavefront Sensorless Adaptive Optics white paper.
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.