Category: Uncategorized

How to see around the corner?

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Researchers at Heriot-Watt University in Edinburgh, Scotland have recently developed a super sensitive camera that could detect what is hidden behind the corners. The camera is called single-photon avalanche diode (SPAD) camera and using the photons echo mapping technique, it is possible to see beyond the line of sight!

Actually this technique is really not that new. In 2012, MIT researchers announce that they have developed a camera that can capture trillion frame per second. Using it, it is possible capture the photons that reflected from object or person around the corners.

Cool right ?

 

 

Tutorial 102: How to select a f-theta objective for your scanner ?

laser-material-processing-with-jenar-f-theta-jan

f-theta objective is normally used together with a galvo-based laser scanner. It has 2 main functions: focus the laser spot and flatten the image field, as shown in the image below. The output beam displacement is equal to f*θ, thus was given the name of f-theta objective. Current leading companies for f-theta objectives includes SILL optics, Jenoptik , LINOS, ULO, II-IV etc.

FTH100-1064_dwg3_1200

Left: typical scan field with curvature using single focusing lens. middle: typical result of a flat field lens. Right: flat field objective can provide flat field and f*θ at the output (Source: Thorlabs).

By asking the following questions, it is possible to narrow down the selection of the scanning objectives:

  • What is the laser parameters (wavelength, average power, pulsed or CW?) -> determine the AR coating and the lens materials.
  • What is the required image field size and focused spot size? -> determine required focal length.
  • Is the telecentricity properties of the f-theta objective important? -> determine whether you would need a telecentric lens. For example, drilling application

So what to look at when shopping for a f-theta?

  • focal length
  • output beam quality
  • clear aperture of the objective
  • telecentric or not?
  • lens materials ?
  • achromatic or not?
  • Would thermal shift be an issue ?

In general, a diffraction limited f-theta combined with a scanner would produce a spot size given by:

Spot size (1/e²) = (λ• f • APO • M²) / Dg, where APO is the truncation factor that depend on the ratio between aperture stop of the scanner and input beam diameter. Different ratio will give different APO value, as shown below:

Da/Dg APO
2.0 1.27
1.5 1.41
1.25 1.56
1.0 1.83
0.9 1.99
0.75 2.32
0.5 2.44

As for other Da/Dg ratio, one can estimate the APO using hyperbolic tangential function or the formula stated in  “CVI Melles Griot All things Photonics”

Source: Jenoptik, Sill Optics & Thorlabs

WANNA BUILD YOU OWN SLS 3D-PRINTER?

Instead of paying hundreds pf thousands of dollars for a Selective Laser Sintering printer, why not try to build it for $2000 ? Rice University researcher has recently demonstrated that it is possible to develope a low-cost, open-source SLS system (OpenSLS) and demonstrated its capacity to fabricate structures in nylon with sub-millimeter features and overhanging regions.

journal.pone.0147399.g001

Source:http://journals.plos.org/plosone/article?id=10.1371/journal.pone.0147399

 

Laser + Glass – you got yourself a 360GB memory that last for hundred of millions years

Imagine the Superman using his laser beam eye to store information in the memory crystals in the Fortress of Solitude. Too bad,  he cannot create femtosecond pulsed with his eyes.

CW-STM-Fortress-28source: capedwonder

Hitachi has developed a glass-based data storage medium that is highly heat and water resistant, capable of holding data for hundreds of millions of years, and says it may be able to bring it to market by 2015.The company’s main research lab has developed a way to etch digital patterns into robust quartz glass with a laser at a data density that is better than compact discs, then read it using an optical microscope. The data is etched at four different layers in the glass using different focal points of the laser.

The company has tested the durability of the quartz glass it uses and determined that it will last for “hundreds of millions of years.” It said samples held up to two hours of exposure to 2000-degree-Celsius heat in an accelerated aging test. Hitachi said it first conceived of the idea of storing data by etching it into quartz glass in 2009, but read and write times remained an issue. The company uses tiny dot patterns to store bits, and has recently developed a way to etch 100 dots at a time, greatly improving the write time.

Recently the scientists at the University of Southampton have made a major step forward in the development of this digital data storage.Using nanostructured glass, scientists from the University’s Optoelectronics Research Centre (ORC) have developed the recording and retrieval processes of five dimensional (5D) digital data by femtosecond laser writing.

The storage allows unprecedented properties including 360 TB/disc data capacity, thermal stability up to 1,000°C and virtually unlimited lifetime at room temperature (13.8 billion years at 190°C ) opening a new era of eternal data archiving. As a very stable and safe form of portable memory, the technology could be highly useful for organisations with big archives, such as national archives, museums and libraries, to preserve their information and records.

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How does it works?

5D data storage.jpg_SIA_JPG_fit_to_width_INLINE

To record data, spots are imprinted on the glass (pictured below) using a femtosecond laser. A femtosecond laser, in this case, produces bursts of laser light that last for just 280 femtoseconds (280 quadrillionths of a second). These spots, thanks to the nanostructuring of the surface, and some hologram cleverness, are capable of recording up to three bits of data in two “dimensions.” By varying the focus of the laser, the team are able to create layers of dots that are separated by five micrometers (0.005mm) in the z-axis (the third dimension). Then, by simply moving the laser horizontally and vertically, these tri-bits can be stored in two more dimensions, bringing the total to 5D. The image at the top of the story helps illustrate this concept.

To read these spots, an optical microscope that’s capable of untangling the polarized light reflected by the three-bit spots is used. There’s no word on whether these silica glass discs can be rewritten, but the research paper makes it sound like this is a write-once-read-many (WORM) storage method.

Source: University of Southhampton; Extremetech; Hitachi

LASER IS NOT ONLY FOR NERDS

IMG_9900-Edit

DOUG AITKEN’S STATION to Station, which took a crew of visual artists and musicians from New York to California aboard a nine-car train, brought together digitized modern creativity and the distinctly analog appeal of the great American road trip. They rode the rails, they performed, they stopped and collaborated with locals, and streamed it all online. Now Aitken has synthesized the three-week experience into a documentary of 62 one-minute highlights,available on iTunes starting Jan. 15.

In the above clip from the documentary, data visualization artist Aaron Koblin (now the CTO of virtual reality company Vrse) explains Light Echoes, the product of a collaboration between himself and director Ben Trickleback. In Koblin’s words, it’s their way of “mapping the history of the train on top of the landscape.” The twist is that their cartography is accomplished with a giant array of lasers projecting images onto train tracks. The vividly colored result is a trail of light that looks as organic as it does alien.

WELL DONE LAD!

SOURCE: WIRED

WHAT CAN YOU DO WITH A GALVO?

Several months ago someone asked me: what is a galvo scanner ? What can it do? Isn’t it just a mirror that can move? What so cool about it?

Here is a list of cool things that you could do using galvo scanners:

  1. Laser light show

high speed galvo

2. Laser marking: you can always give your iphone a new permanent Tattoo:

hairy_crab_01

3. Laser engraving:

4. Paper/Leather/ Textile cutting: Still cutting the paper with a scissors? it is so 1980s.

5. Laser Welding:

6. Jeans engraving: let’s give your jeans a new skin

7. Laser in glass engraving: an christmas present idea for you.

8. Micro machining/ micro-3D printing: # nanoscribe

8. Selective Laser Melting – SLM

9.  Laser drilling

10. Medical : Optical coherence tomography (OCT)

JMI_2_2_026003_f001 (1)

 

WHAT ELSE ?

 

 

 

 

 

PHOTONICS 101 FOR DUMMIES

SPIE has collaborated with SPECTARIS, the German Hightech Industry Association, on an English version of its popular Photonics infographic book, Photonik: Technische Anwendungen des Lichts – Infografiken.

In 2015, SPECTARIS and industry sponsors in Germany published the original, German-language book to promote photonics to a broad audience during the International Year of Light.

There was a high level of interest in the book from the technical community, and the collaboration with SPIE Press will permit sharing an English-language book, Photonics: Technical applications of light – infographics, with an even larger audience.

The book covers basic concepts in photonics as well as image capture technologies and photonics applications in healthcare, environmental monitoring, and displays.

A PDF of the English version is available for free download from SPIE (19 MB) and at the SPIE booth at Photonics West in February.

HERE ARE SOME HIGHLIGHTS:

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SOURCE: SPIE.org

TUTORIAL 1: How to choose a galvo scanner?

800px-Plexi_Galvohalter

There are several methods for the laser beam steering. The most common method would be the nanopositioner/ piezo-translation stage. It can move with high precision but low speed due to the large inertial. The counterpart galvo- scanner ( or simply galvo) offers high speed scanning and less expensive solution with the tradeoff of precision. In this tutorial, I will summarize the features that one should notice for choosing the galvo scanner ( 1D or 2D).

What the hell is galvo?

In a Nutshell, galvo scanner is high speed moving mirrors. A galvo system mainly consist of 3 components: motor, mirror and driver board. If the user would like to control the system with digital signals, then they will include a D/A converter to do the job. Otherwise, they can control the movement using analog control (voltage).

scanner CTIsource: Cambridge Technology

Motor/ galvanometer selection

Three important components in a galvanometer: rotor, stator and position detector (PD). The performance of the rotor + stator dictate the torque efficiency whereas the position detector dictate the performance of the system. Here we will not cover the topics of rotor/stator performance and user should refer the “Handbook of optical and laser scanning” by Gerald F. Marshall for more information.

The PD plays an important role in the performance of the galvanometer. The latest design of the PD involves the illumination diode(s),mask and photodector(s). There are several specifications of PD that one should aware of:

i) Linearity: how the PD behaves as an ideal linear transfer function. Typical values: 99.5%- 99.9%

ii) Repeatability:  describe the consistency of PD when return to a specific position, typical values: 1µrad – 8µrad.

iii) long term stability (drift): describe how the system behaves over time and temperature. Usually described by Offset drift (deviate from the 0,0 position) and Gain drift (deviation between set and real position).

Mirrors selection

The basic function of the mirrors is to accommodate the input laser beam and cover the entire beam over the scan angles.  The mirror thickness, size, shape, material and the moment of inertial of the mirror play an important on the performance of system. Especially when the system is subjected to the high acceleration during operation, the mirror must remain rigid or the speed or the accuracy of the system would be compromised. So what should you look at when searching for the galvo mirrors?

i) shape and size:  the shape and size of the mirror are normally defined / fixed by the manufacturers, since the tunings are based  on the geometry of the mirror .

ii) substrate materials: common used materials are silicon, fused silica, beryllium or silicon carbide. Each material has their own pro and cons. For more information, we would recommend the read the following article.:

http://www.laserfocusworld.com/articles/print/volume-45/issue-3/features/optics-for-scanning-rapid-scanning-applications-drive-mirror-design.html

iii) Optical coating: each mirror must designed and customized according to the laser wavelength and laser power. Beside the broadband metallic coating, the commonly used Laser mirrors consist of multilayers dielectric layers and could provide >99% of reflectivity. Other than the reflectivity, there are several parameters that one should look at when shopping for the appropriate laser mirrors. The most important properties are surface quality, surface flatness and the laser damage threshold:

Optical Surfaces 

Surface Quality

The surface quality of an optic is described by its surface figure and irregularity. Surface figure is defined as peak-to-valley deviation from flatness, including any curvature (also known as power) present. Surface irregularity is represented by the peak-to-valley deviations when power is subtracted. The front-surface figure is typically guaranteed flat to less than λ/10 at 633 nm over the clear aperture. Our 2″ mirrors have a typical figure of λ/4 over the clear aperture. When preservation of wavefront is critical, choose a flatness of λ/10 or better.
As for surface quality, the smaller the scratch-dig specification, the lower the scatter. Our metal mirrors offer a scratch-dig of 25-10; our dielectric mirrors, 15-5; and our UV mirrors, 10-5, which is ideal
for the most demanding laser systems where low scatter is critical.
dig: a defect on the surface of an optic as defined in average diameter in 1/100 of a millimeter.
scratch: a defect on an optic that is many times longer than it is wide.

The mirror application drives the requirements for surface flatness and surface quality. When preservation of wavefront is critical, a λ/10 to λ/20 mirror should be selected; when wavefront is not as important as cost, a λ/2 to λ/5 mirror can be used. For surface quality, the tighter the scratch-dig specification, the lower the scatter. For demanding laser systems, 20-10 to 10-5 scratch-dig is best. For applications where low scatter is not as critical as cost, 40-20 to 60-40 scratch-dig can be used.

Surface Flatness

Figure Cost Applications
λ/2 Low Used where wavefront distortion is not as important as cost
λ/5 Moderate Excellent for most general laser and imaging applications where low wavefront performance must be balanced with cost
λ/10 Moderate For laser and imaging applications where low wavefront distortion, especially in systems with multiple elements
λ/20 High For the most demanding laser systems where maintaining accurate wavefront is critical to performance

Surface Quality

Scratch-Dig Cost Applications
60-40 Low Used for low-power laser and imaging applications with unfocused beams where scatter is not critical
40-20 Moderate Ideal for laser and imaging applications with collimated beams where scatter begins to affect system performance
20-10 High Excellent for laser systems with focused beams that can tolerate little scattered light
10-5 High For the most demanding laser systems where low scatter is critical to performance

Source: Newport

LASER DAMAGE THRESHOLD  (LDT)

Coating selection (1)

Normally the specification of laser damage threshold of a mirror is specified by the manufacturers and should not be exceeded, otherwise delamination or burn out could occur (Figure below)

OE_52_8_086103_f005source: SPIE Library

Depending on the laser operation mode, the laser induced damage mechanism are different. In the case of continuous wave (CW) or Quasi- CW operation, the damage is usually caused by the thermal effect due to the absorption. As for the case of pulsed operation, especially pulsed duration in the pico- or femto seconds range, the damage is caused by the dielectric breakdown. So when assessing the LDT of the mirrors, it is essential to ask the following questions:

  1. CW or pulsed operation?
  2. What is the power /energy density of your beam (total power/energy divided by 1/e2area)
  3. Pulse length of your lase
  4. Pulse repetition frequency (prf) of your laser
  5. Beam diameter of your laser (1/e2)

For more information please refer to the Thorlabs LDT Tutorial:

https://www.thorlabs.de/newgrouppage9.cfm?objectgroup_id=7040

Driver boards selection

There are not much of choices when come the driver boards/servos. It can either be digital or analog control. Analog servos do the job with lower price, however, the tunings have to be performed manuals and is normally coupled to the particular galvos. Digital servos are more expensive but offer better performance and extra features.

 

What cool things you can do with Direct Laser Writing (a.k.a 3D printer)?

I am not talking about the cheap $500 material jetting/extrusion based 3D Printer nor the $5,000 Vat Photopolymerzation technique based steoreolithagraphy (http://3dprinting.com/what-is-3d-printing/). Here I am talking about the $500K 3D laser direct laser writing machine  that is wide used for micro-structure fabrication. In this technology, fs pulsed laser is tightly focus on the photosensitive resin and the tiny exposed area undergo  es two photons polymerization (TPP) and by moving this focused spot, one can create 3D structures in the submicron size.  I was lucky enough to involve several projects that fabricate structures using the Nanoscribe machine.

Alumina infiltrated octohedral structure
alumina-polymer_octohedral

Now back to the topic- what can you do with such a sophisticate machine ?

1. Rapid prototyping- in the micron scale. Previously, such a system has been used only in research laboratories since the process is quite time consuming. 100mm2 structure would normally take several days.  The latest  model utilizes high speed galvo mirrors and increases the speed by at least ten folds.

tajneedle
source: Nanoscribe

2. 3D Photonic Structures

nanoscale03A1_5_3D_gold_helix_metamaterial_rdax_1200x901
Left: 3D Photonic Crystals; Right: Gold helix metamaterial

3. Micromachine (Magnetic Sperm)

A research group at ETH Zurich successfully fabricated sperm shaped microrobots and control them using magnetic field.

4. Photonics Phase arrays / Optical filter

Researches at TU Hamburg has demonstrated that it is possible to create diffractive optics element using 3D printing technique. The waveguide based phase arrays allow user to encode their message into the structure and projected it later using the appropriate laser. The potential application is the anti-counterfeiting.

hologram
source: TUHH

5. Mechanical structures with nano/micro- lattices.

Several groups are currently investigating how the material + structures (lattice) influence the mechanical properties of the hierarchical structure.

jam_082_07_071012_f003 (1)

source: CALTECH

6. Medical applications

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Left:Polymer scaffold for cell culture; Right: Microneedless