ArticlePDF Available

Abstract and Figures

Circular surface-relief diffraction gratings with a constant pitch were photo-inscribed on thin films of a disperse red 1 functionalized glass-forming compound using a novel holographic technique. Various light-interfering metallic fixtures, which consisted of annular rings with a sloped and polished inner surface, were designed and fabricated. Each of them allowed the inscription of stable and high-quality circular diffraction gratings with pitches ranging from approximately 600–1400 nm and depths up to 250 nm. This was accomplished by exposure to a collimated laser beam with an irradiance of 604 mW/cm2 for 350 s. The resulting gratings had a diameter of 11.4 mm and had the advantage of being produced in a simple single-step procedure with no postprocessing or specialized equipment. The pitch and diameter of these circular gratings were dependent on the fixture geometry, while the depth was related to the exposure time.
Content may be subject to copyright.
This paper was published in Optics Letters and is made available as an electronic reprint
with the permission of OSA. The paper can be found at the following URL on the OSA
Systematic or multiple reproduction or distribution to multiple locations via electronic or
other means is prohibited and is subject to penalties under law.!
Design and fabrication of constant-pitch
circular surface-relief
diffraction gratings on disperse red 1 glass
James Leibold,1Peter Snell,1Olivier Lebel,2and Ribal Georges Sabat1,*
1Department of Physics, Royal Military College of Canada, P.O. Box 17000, STN Forces, Kingston, ON, K7K7B4, Canada
2Department of Chemistry and Chemical Engineering, Royal Military College of Canada, P.O. Box 17000,
STN Forces, Kingston, ON, K7K7B4, Canada
*Corresponding author:
Received March 12, 2014; revised May 2, 2014; accepted May 2, 2014;
posted May 5, 2014 (Doc. ID 208089); published June 5, 2014
Circular surface-relief diffraction gratings with a constant pitch were photo-inscribed on thin films of a disperse red
1 functionalized glass-forming compound using a novel holographic technique. Various light-interfering metallic
fixtures, which consisted of annular rings with a sloped and polished inner surface, were designed and fabricated.
Each of them allowed the inscription of stable and high-quality circular diffraction gratings with pitches ranging
from approximately 6001400 nm and depths up to 250 nm. This was accomplished by exposure to a collimated
laser beam with an irradiance of 604 mWcm2for 350 s. The resulting gratings had a diameter of 11.4 mm and had the
advantage of being produced in a simple single-step procedure with no postprocessing or specialized equipment.
The pitch and diameter of these circular gratings were dependent on the fixture geometry, while the depth was
related to the exposure time. © 2014 Optical Society of America
OCIS codes: (050.1950) Diffraction gratings; (050.1970) Diffractive optics; (050.2770) Gratings; (050.6875) Three-
dimensional fabrication; (090.1970) Diffractive optics; (310.6860) Thin films, optical properties.
Surface relief diffraction gratings (SRGs) can be pro-
duced by a variety of methods. Patterns can be directly
imprinted onto a resist through electron beam lithogra-
phy [1] or directly engraved into materials with focused
ion beams [2] or laser milling [3]. These methods can be
time consuming for large grating areas since each line is
drawn individually. Photolithography is widely used in
industry and involves using a photomask to expose an
entire pattern onto a photoresist. It is convenient for cre-
ating large, complex patterns and can be combined with
other microfabrication techniques [4], but it requires
multiple processing steps. Nanoimprinting involves
production of a mold, sometimes from a method listed
above, which is then pressed into a polymer surface
[5]. Although it is appropriate for mass production of a
pattern, it is also a multiple step process that is ill suited
for rapid development of new grating patterns. Direct
laser interference patterning utilizes interference of
coherent light to directly engrave surface patterns on
commercially available polymers [6]. This method is a
single step process, but the ablation of material requires
a high-powered pulsed laser.
The production of SRGs using materials containing
azobenzene chromophores has proven to be an interest-
ing area of study [7]. A thin film of an azopolymer
material, such as disperse red 1 (DR1) Poly(methyl meth-
acrylate) (PMMA), has the ability to record holographic
information in surface relief because of its photosensitive
mass transport properties. These SRGs also have the abil-
ity of being thermally erased and optically rewritten [8].
Although the mechanism is not fully understood, there
are successful models which explain the material trans-
port as the result of changes to the elastic properties of
the material when it is exposed to light [9]. Other papers
have reported on the properties of DR1-functionalized
glass-forming compounds [10]. Our group has recently
synthesized a new azoglass compound, which possesses
the added benefits of easier purification, higher yield, and
the production of high-quality thin films and SRGs [11].
The goal of this Letter is to introduce a novel method of
inscribing circular SRGs onto azoglass films using a
three-dimensional (3D) beam splitting technique with a
fixture called a circular diffraction grating generator
(CDG). There have been other publications on the forma-
tion of circular diffraction gratings using interference
patterns from standing spiral waves [12], Bessel beams
[13], and fiber optic modes [14]; however, our technique
is novel in its production method, and our circular gra-
tings are created on a much larger scale than previously
reported. Possible applications for this new technique
may include: optical sensors [15], enhancement of LEDs
[16], improvements in solar cell efficiency [17], plas-
monic lenses [18], circular grating distributed feedback
dye laser [19], and optical measuring techniques [20].
Assume a mirror in the shape of a hollow truncated
cone. The inner surface of this shape is reflective and
is the basis for a theoretical CDG. When a collimated la-
ser beam, with a diameter sufficiently large to illuminate
the entire reflective surface, is incident normally, the
CDG will reflect the light toward the smaller aperture
end, creating interference at the center with the directly
incident light. This interference yields a pattern of circu-
lar constant-pitch concentric rings with sinusoidal
intensity variation that can be photoinscribed on an
azoglass film placed at the back of the CDG along
the smaller aperture end.
If the angle of the mirrored surfaces of the CDG could
be changed, it would modify the circular grating pitch.
Figure 1shows a schematic of a planar wave front inci-
dent onto a CDG where θis the angle of the mirrored
surface from the normal. At points Aand B, the colli-
mated wave front will be in phase. Using the law of sines
June 15, 2014 / Vol. 39, No. 12 / OPTICS LETTERS 3445
0146-9592/14/123445-04$15.00/0 © 2014 Optical Society of America
with triangle ACD, it can be shown that AC DC cot θ.
Using triangle ABC, it can be shown that BC
AC cos 2θ. Substituting these two equations to find the
difference in path length AC BC, along with the use
of trigonometric identities, gives
AC BC DC sin 2θ:(1)
The phase difference δis related to the optical path
length difference as δkAC BCπ, where kis
the wavenumber for the light source k2πλ, and the
additional term of πis the phase change from the reflec-
tion on the CDG mirror. In order to find the pitch
between each maxima or minima, we can state that
2πkAC BC. By substituting Eq. (1) and isolating
the length DC, it can be found that for a given CDG angle
θ, the grating pitch Λis given by
Λλcsc 2θ:(2)
This equation demonstrates a practical limit to the small-
est grating pitch that can be generated, which is depen-
dent on the wavelength of the light source and is limited
to Λλas θapproaches 45 deg. At CDG angles greater
than or equal to 45 deg, the reflected light will never
reach the sample surface, and no interference pattern
will be generated.
A similar geometric analysis of Fig. 1shows that a
maximum height yof the CDG is constrained by the ra-
dius of the smaller CDG aperture xand is dependent on
the angle of the CDG θ. This is given by the following
tan 2θtan θ:(3)
If the actual height of a CDG is larger than the maximum
height ypredicted by Eq. (3), then the reflected beams
will pass the center point of the sample. This will cause
cross interference with the reflected beam from the op-
posite side of the CDG and will decrease the quality of the
SRG being generated. If the actual height of the CDG is
smaller than yfrom Eq. (3), then the resulting interfer-
ence pattern will not reach the center of the sample re-
sulting in a ring grating with a smooth circular center.
Several CDG fixtures were machined and polished us-
ing manual equipment found in common machine shops.
Care was taken to ensure that the reflecting conical
surface was a true truncated cone, finishing at a knife
edge on the minor aperture, with its central axis
perpendicular to the flat face. The material used was
high-quality annealed carbon steel. After machining,
the CDG fixtures were washed with solvent and dried
with air. Approximately 500 nm of silver was then sputter
coated onto each CDG in order to create a mirror-like
finish. A total of five CDGs were machined with angles
θof 12.5, 20.8, 23.5, 31.2, and 40.4 deg.
Azoglass was synthesized according to [11]. Solutions
of azoglass were then prepared from powder by mixing
with dichloromethane at 3 wt. % concentration. The sol-
ution was subsequently mechanically shaken and filtered
with a 50-μm filter. Solid films were fabricated by spin
casting the solution onto cleaned and dried microscope
slides. At a rate of 1500 rpm, the solid films had a thick-
ness of approximately 400 nm, as measured with a
An azoglass sample was placed directly on the CDG
facing the small aperture. The beam from a Verdi diode-
pumped laser with a wavelength of 532 nm was passed
through a spatial filter, collimated, and circularly polar-
ized by a quarter-wave plate. The resulting collimated
beam had an irradiance of 604 mWcm2. The beam diam-
eter was controlled by a variable iris and was projected
onto the CDG and sample.
Real-time data of the diffraction efficiency at a local-
ized point of the circular SRG is shown in Fig. 2as a func-
tion of exposure time. This was accomplished by shining
a low-powered HeNe laser onto the sample where
the grating was forming. This laser was mechanically
chopped, and the first-order diffraction beam was
incident onto a silicon photodiode. The signal from the
photodiode was amplified by a lock-in amplifier and plot-
ted as a function of time on a computer. The diffraction
efficiency was calculated by dividing the first-order dif-
fracted signal by that of the incident beam, which was
measured in a similar manner. The steady increase
and eventual plateau of the diffraction efficiency for ex-
posures up to about 300 s is likely due to the physical
migration of the molecules of the azoglass as they are
being displaced to form peaks and troughs of greater
depths. Based on the results of this plot, efficient circular
SRGs can be generated with exposure times greater than
Fig. 1. Schematic demonstrating the optical geometry of a
cross section of a CDG.
Fig. 2. Typical localized diffraction efficiency of circular SRG
in real time as it is inscribed by a CDG. The sudden drop just
after 600 s is attributed to when the inscribing laser is turned
off. Inset (a): Circular SRG produced in azoglass and coated
with gold. Inset (b): Circular diffraction pattern from SRG.
3446 OPTICS LETTERS / Vol. 39, No. 12 / June 15, 2014
300 s. Nonetheless, for the remainder of this experiment,
an exposure time of 350 s was arbitrarily chosen.
Circular SRGs, with a diameter of approximately
11.4 mm, were inscribed using the method described
above, as seen in Fig. 2, inset (a). To verify that circular
gratings were actually created, a collimated beam from a
HeNe laser was used to illuminate the SRG resulting in
the circular diffraction pattern photographed in transmis-
sion 1 cm away from the sample, as seen in Fig. 2,
inset (b).
Atomic Force Microscopy (AFM) imagery of the sur-
face profile of a circular SRG was taken, and an example
is presented in Fig. 3. The AFM scans show a regular sine
wave pattern aligned radially from the center of the
circular SRG. The generated SRGs had depths of up to
250 nm, depending on laser exposure time. The total dis-
tances between multiple peaks were obtained from the
AFM imagery and divided by the number of complete
waves to get an average grating pitch for each scan.
To further improve the accuracy of the results, scans
were taken at the 0°, 90°, 180°, and 270° positions of each
circular grating, and these results were averaged again.
The black circle points in Fig. 4represent AFM measure-
ments of grating pitches taken by this method. AFM
scans of the smooth center area of circular SRGs created
with a CDG having a height less than the theoretical y
from Eq. (3) do show evidence of random self-structuring
formations; however, these are on the order of 20 times
shallower then the gratings formed in the interference
In order to verify that there were no unpredicted large-
scale effects, a scanning electron microscope (SEM) was
used to image larger SRG areas (on the order of 150 μm),
as seen in Fig. 5. Circular SRGs, generated from the 12.5,
20.8, 31.2, and 40.4 deg CDGs, were sputter coated with
approximately 60 nm of gold and observed in the SEM.
Individual gratings could still be visually resolved at
magnifications of up to 2000 times. The grating pitches
were measured at a magnification level of 15000 times,
and these data points are included on Fig. 4as crossed
The third and last method for obtaining the grating
pitch of these circular SRGs was done by measuring
the diffraction angle from a low-powered HeNe laser in-
cident on a small portion of the grating. The resulting
first-order diffracted beam was an arc of a circle. How-
ever, since the laser beam illuminated only a small area
near the edge of the circular grating, it can be approxi-
mated as a linear diffraction grating since the radius of
curvature of the grating is relatively large compared to
the small area being illuminated. Therefore, the well-
known grating equation for normal incidence was used
to calculate the grating pitch Λ. Accurate measurements
of the first order diffraction angle were obtained using a
Velmex rotary stage connected to a computer. Hollow
square points in Fig. 4represent grating pitches calcu-
lated by this method.
The results in Fig. 4demonstrate that the three inde-
pendent methods of measuring the circular grating
pitches written on azoglass samples by CDGs are con-
sistent and correlate very well with the predicted theory
given by Eq. (2).
Five circular SRGs, with pitches from 600 to 1400 nm
and depths of up to 250 nm, were photoinscribed onto
azoglass films using a novel holographic technique
made possible with a fixture called a CDG. The fact that
the SRGs formed are circular is supported by the
Fig. 3. AFM scan of circular SRG generated by a 20.8 deg
Fig. 4. Theoretical and measured results of the SRG pitch ver-
sus CDG mirror angle θ. Measured results include data points
taken from AFM, SEM, and diffraction angle measurements.
The theoretical curve is plotted using Eq. (2).
Fig. 5. SEM image of circular SRG generated from a 20.8 deg
CDG. (a) At 2000 times magnification, the grating peaks can be
visually resolved showing a highly regular grating pattern.
(b) At 15000 times magnification gratings are clearly resolved.
June 15, 2014 / Vol. 39, No. 12 / OPTICS LETTERS 3447
orientation of the gratings measured in the AFM scans as
well as the circular diffraction pattern produced by illu-
minating the SRGs. The SRG depth and, to a certain ex-
tent, the diffraction efficiency can be varied depending
on the inscribing laser irradiance and the amount of
exposure time. The SRG pitches were measured using
a variety of techniques and agreed very well with the
theoretical predictions, which are dependent on the
CDG geometry and wavelength of the inscribing light.
The inside and outside diameters of the circular SRGs
generated by this method can also be controlled by
varying the size of a CDGs smaller aperture xand height
y. The main advantages of this method are that it is a
single step, direct inscription process that produces
SRGs that can be thermally erased and optically rewrit-
ten. It has relatively fast SRG production times on the
order of 300 s with grating sizes only limited by the
diameter of the collimated laser beam used to inscribe
1. C. Vieu, F. Carcenac, A. Pepin, Y. Chen, M. Mejias, A. Lebib,
L. Manin-Ferlazzo, L. Couraud, and H. Launois, Appl. Surf.
Sci. 164, 111 (2000).
2. D. Moss, V. Taeed, B. Eggleton, D. Freeman, S. Madden, M.
Samoc, B. Luther-Davies, S. Janz, and D. Xu, Appl. Phys.
Lett. 85, 4860 (2004).
3. L. Shah, M. E. Fermann, J. W. Dawson, and C. P. Barty, Opt.
Express 14, 12546 (2006).
4. K. Rastani, A. Marrakchi, S. F. Habiby, W. M. Hubbard, H.
Gilchrist, and R. E. Nahory, Appl. Opt. 30, 1347 (1991).
5. Y. Chen, Z. Li, Z. Zhang, D. Psaltis, and A. Scherer, Appl.
Phys. Lett. 91, 051109 (2007).
6. A. Lasagni, D. Acevedo, C. Barbero, and F. Mücklich, Adv.
Eng. Mater. 9, 99 (2007).
7. A. Priimagi and A. Shevchenko, J. Polym. Sci. B 52, 163
8. P. Rochon, E. Batalla, and A. Natansohn, Appl. Phys. Lett.
66, 136 (1995).
9. M. Saphiannikova, V. Toshchevikov, and J. Ilnytskyi,
Nonlinear Opt. Quantum Opt. 41, 27 (2010).
10. H. Audorff, R. Walker, L. Kador, and H. Schmidt, Proc. SPIE
7233, 72330O (2009).
11. R. Kirby, R. G. Sabat, J. Nunzi, and O. Lebel, J. Mater.
Chem.C 2, 841 (2014).
12. J. P. Vernon, S. V. Serak, R. S. Hakobyan, A. K. Aleksanyan,
V. P. Tondiglia, T. J. White, T. J. Bunning, and N. V.
Tabiryan, Appl. Phys. Lett. 103, 201101 (2013).
13. T. Grosjean and D. Courjon, Opt. Express 14, 2203
14. J. K. Kim, Y. Jung, B. H. Lee, K. Oh, C. Chun, and D. Kim,
Opt. Fiber Technol. 13, 240 (2007).
15. R. D. Bhat, N. C. Panoiu, S. R. Brueck, and R. M. Osgood,
Opt. Express 16, 4588 (2008).
16. J. Zhu, H. Zhang, Z. Zhu, Q. Li, and G. Jin, Opt. Commun.
322, 66 (2014).
17. B. Janjua and G. Jabbour, in 2013 IEEE Photonics
Conference (IPC) (IEEE, 2013), pp. 578579.
18. J. M. Steele, Z. Liu, Y. Wang, and X. Zhang, Opt. Express 14,
5664 (2006).
19. Y. Chen, Z. Li, M. D. Henry, and A. Scherer, Appl. Phys. Lett.
95, 031109 (2009).
20. H. M. Shang, S. L. Toh, Y. Fu, C. Quan, and C. J. Tay, Opt.
Lasers Eng. 36, 487 (2001).
3448 OPTICS LETTERS / Vol. 39, No. 12 / June 15, 2014
... Independent of its flexibility in defining feature size, the SLM is particularly versatile in generating on-demand surface structures with a rich diversity of geometrical configurations. As one example, consider circular microstructures, which find use as distributed feedback structures in polymer lasers and as diffractive lenses or kinoforms [30][31][32]. Figure 5 shows the SLM pattern and the resulting surface relief circular gratings, respectively. The circular grating has a pitch of 1.1 µm and was obtained with a single 5 sec exposure. ...
Full-text available
A versatile system for the fabrication of surface microstructures is demonstrated by combining the photomechanical response of supramolecular azopolymers with structured polarized illumination from a high resolution spatial light modulator. Surface relief structures with periods 900 nm - 16.5 µm and amplitudes up to 1.0 µm can be fabricated with a single 5 sec exposure at 488 nm. Sinusoidal, circular, and chirped surface profiles can be fabricated via direct programming of the spatial light modulator, with no optomechanical realignment required. Surface microstructures can be combined into macroscopic areas by mechanical translation followed by exposure. The surface structures grow immediately in response to illumination, can be visually observed in real time, and require no post-exposure processing.
... Several different geometries of SRGs have been reported thus far such as linear, superimposed, crossed and circular grating patterns [14,[16][17][18][24][25][26][27][28]. One of those SRG geometries is the crossed surface relief gratings (CSRG) which is made by orthogonally superimposing linear SRGs during the fabrication process through sequential laser beam inscription on the azo-film. ...
Full-text available
Plasmonic crossed surface relief gratings were fabricated using interference lithography. Their topographies were studied by AFM as a function of laser exposure time and their surface plasmon resonance at a gold-air interface was measured between crossed polarizers in transmission and in reflection modes. Both modes resulted in emitted plasmonic light at specific wavelengths related to the grating pitch, with the reflectance SPR having a much higher intensity than the transmittance SPR. The use of these gratings as plasmonic sensors was examined and their sensitivities were measured in the reflectance and transmittance modes to be 601 nm/RIU and 589 nm/RIU, respectively.
... Various shapes of nanostructures or diffraction gratings can be inscribed by exposing the azobenzene film to a laser interference pattern of the desired shape and structure. For instance, circular [19] and non-uniform surface relief gratings [20] have been fabricated in our group. ...
Full-text available
Two-dimensional chirped-pitch crossed surface relief gratings (CP-CSRGs) were fabricated on azobenzene-functionalized thin films using a simple two-step procedure. The resulting gratings had a constant pitch in one direction and a varying (chirped) pitch in the orthogonal direction. They were coated with silver and tested for their ability to change the polarization of surface plasmon resonance (SPR) signals, when placed between crossed polarizers. It was observed that several different bandwidths of SPR wavelengths are excitable using a single device, making CP-CSRGs suitable as next generation SPR-based sensors. The SPR wavelengths shifted as much as 10.5 nm/mm along the chirped grating, and a maximum sensitivity of 778.6 nm/RIU was obtained when detecting the refractive index change of various concentrations of aqueous sucrose solutions.
... For non-uniform gratings, the directly incident laser beam on the azobenzene film's surface is diverging due to the spherical lens and an additional interference phase angle is imposed to account for the time delay for the beam to reach various areas on the sample's surface. An expression for this additional phase angle has been previously obtained when using a cylindrical lens along the direct laser beam path [22,23]. However, when using a spherical lens, the geometrical analysis of the phase difference between the direct and reflected beams is different since it must account for distance variations both along the X-axis and Y-axis. ...
Full-text available
Non-uniform surface relief diffraction gratings were laser-inscribed on azobenzene molecular glass thin films using a modified Lloyd's mirror interferometer. The azobenzene films were exposed to an adjustable interference pattern produced by the recombination of collimated and spherically divergent laser wave fronts. The localized pitch, grating vector orientation and depth of the resulting non-uniform gratings were measured using an atomic force microscope and a theoretical model was analytically developed to explain the experimental results. The fabricated gratings exhibited a chirping or pitch variation along the imposed X-axis as well as an angular change in the grating vector orientation along the imposed Y-axis. Studies were conducted on various non-uniform grating configurations having central pitches of 500 nm, 1000 nm, 1500 nm and 2000 nm.
A thermo-optical process was developed for the erasure of surface relief gratings (SRG) inscribed on various films of mexylaminotriazine molecular glasses functionalized with different azobenzene chromophores, as well as azobenzene polymer films. Irradiation of the samples with a CO2 laser beam causes localized heating of the soda lime substrate, which is then transferred to the azobenzene films, causing complete erasure of the gratings while the temperature of each film was monitored in real time. The erasure temperature has been found to be strongly correlated with the respective glass transition temperatures (Tg) of the materials. Therefore, complete and partial all-optical erasure of gratings was successfully demonstrated and occurred in under a minute for azobenzene molecular glasses and under 3 minutes for azo-polymer films. Finally, gratings were shown to erase in specific patterns through the use of a metallic mask.
Full-text available
Materials containing azobenzene chromophores exhibit photomechanical behaviors, including the formation of surface relief gratings (SRG) caused by irradiation with two interfering laser beams. While azo-functionalized polymers were extensively studied, small molecules offer the advantage of being monodisperse species, which translates into easier synthesis and purification, as well as more uniform behavior. A drawback is that they tend to crystallize and do not always form high-quality thin films. Glass-forming compounds incorporating azobenzene were previously synthesized in several synthetic steps and in low yield. Herein, a Disperse Red 1 (DR1) functionalized with a mexylaminotriazine group is synthesized in 94% yield using a simple and straightforward procedure. It shows both the ability to form extremely stable glassy phases, and the ability to form SRG in the solid state with growth rates and grating heights closely similar to DR1-functionalized polymers.
Full-text available
Azopolymers comprise a unique materials platform, in which the photoisomerization reaction of azobenzene mole-cules can induce substantial material motions at molecular, mesoscopic, and even macroscopic length scales. In particular, amorphous azopolymer films can form stable surface relief pat-terns upon exposure to interfering light. This allows obtaining large-area periodic micro-and nanostructures in a remarkably simple way. Herein, recent progress in the development of azopolymer-based surface-patterning techniques for photonic applications is reviewed. Starting with a thin azopolymer layer, one can create a variety of photonic elements, such as diffrac-tion gratings, microlens arrays, plasmonic sensors, antireflec-tion coatings, and nanostructured light-polarization converters, either by using the azopolymer surface patterns themselves as optical elements or by utilizing them to microstructure or nanostructure other materials. Both of these domains are cov-ered, with the aim of triggering further research in this fascinating field of science and technology that is far from being harnessed.
Full-text available
A 50 W sub-picosecond fiber chirped pulse amplification system generating 50 µJ pulses at a repetition rate of 1 MHz is demonstrated. As required for precision high speed micro-machining, this system has a practical system configuration enabled by the fiber stretcher and 1780 l/mm dielectric diffraction grating compressor and is capable of ablation rates >0.17 mm3/s metal, ceramic, and glass.
Full-text available
The surface of an azoaromatic polymer film is optically altered to produce local highly efficient diffraction gratings. The gratings obtained are stable but can be erased by heating the polymer above its glass transition temperature and no permanent damage of the film is observed. Multiple gratings can be simultaneously written and gratings can be overwritten. Atomic force microscopy was used to investigate the gratings produced on the surfaces. Possible mechanisms responsible for the surface alteration are discussed.
This review is devoted to the microscopic mechanism behind photoinduced deformations in side-chain azobenzene polymers.We present the analysis of selected experiments that allows us to propose main criteria for a proper choice of the light induced force. Particularly, we provide convincing evidence that, contrary to a well-spread belief, light induced softening is a very weak accompanying effect rather than a necessary condition for the formation of surface relief gratings. Hence, the theories which need a concept of photo-induced softening are not able to describe the phenomenon correctly. Using molecular dynamics simulations, we show that chromophore reorientation alone is capable of the film deformation under homogeneous illumination. Finally, we discuss a recent microscopic theory that satisfies all main criteria for a proper choice of the light induced force. The theory is based on the orientation mechanism of azobenzene chromophores and takes the internal structure of side-chain azobenzene polymers explicitly into account.
Conference Paper
In this paper, design based on tapered circular grating structure was studied, to provide broadband enhancement in thin film amorphous silicon solar cells. In comparison to planar structure an absorption enhancement of ~ 7% was realized.
A scalable and robust methodology for writing cycloidal modulation patterns of optical axis orientation in photosensitive surface alignment layers is demonstrated. Counterpropagating circularly polarized beams, generated by reflection of the input beam from a cholesteric liquid crystal, direct local surface orientation in a photosensitive surface. Purposely introducing a slight angle between the input beam and the photosensitive surface normal introduces a grating period/orientation that is readily controlled and templated. The resulting cycloidal diffractive waveplates offer utility in technologies requiring diffraction over a broad range of angles/wavelengths. This simple methodology of forming polarization gratings offers advantages over conventional fabrication techniques.
This paper proposes a surface-plasmon-enhanced GaN-LED based on the multilayered rectangular nano-grating. This structure contains a SiO2 film, a Ag film and a HfO2 film sequentially coated on the rectangularly-patterned p-GaN layer. The Ag film is used to enhance the internal quantum efficiency. The HfO2 cover-layer symmetrizes the distribution of refractive index besides the Ag film to improve the light extraction efficiency and surface-plasmon (SP) extraction efficiency. The inserted SiO2 layer is utilized to further improve the SP extraction efficiency. The properties of SP modes and Purcell effect in this structure are investigated. The photoluminescence experiments demonstrate that its peak intensity of top-emission is about 2.5 times greater than that from the reference structure covered by a single-layer Ag film on the rectangularly-patterned p-GaN layer.
The formation of phase and surface relief gratings in low-molecular-weight organic glasses containing azobenzene moieties has been studied with holographic methods. Advantages of this class of materials are the simple synthesis, the perfectly amorphous phase, and the possibility of blending them with polymers. Surface relief gratings are formed very efficiently in molecular glasses, and this process can be explained by the gradient force model. Heights up to 610 nm were measured; the temporal evolution of the diffraction efficiency could be reproduced in computer simulations. For technical applications, the surface relief gratings can easily be duplicated by replica molding. Since surface gratings are detrimental to holographic data storage at high densities, it is also possible to suppress their formation by using proper polarizations of the writing beams. Reorientation of the azobenzene groups in the bulk of the glasses and angular multiplexing was demonstrated and the thermal stability of the corresponding phase gratings was studied. Different combinations of molecular cores and substituents at the azobenzene moieties were investigated to find the best systems which yield a high sensitivity and fast grating build-up.
A single-step process for the production of organized surface architectures on the commercial polymer films by direct laser interference patterning (DLIP) is discussed. The DLIP method permits the fabrication of repetitive one dimensional (1D) and two dimensional (2D) patterns and microstructures by direct irradiation of the sample surface with coherent beams of light. The results shows that the previously calculated interference patterns could be directly produced on polymeric surface. The cross-section of the structured polymers changes depending on the intensity of the laser beams. The photomachinability of polymers was highly influenced by laser wavelength. High absorbance of the polymeric materials at specific wavelengths allows the reduction of the intensity of the laser required to achieve a determined structure depth.