Supplementary Material--_058145APL

Supplementary Material
Flexible distributed-feedback colloidal quantum dot laser
Yujie Chen,1, a) Benoit Guilhabert,1 Johannes Herrnsdorf,1 Yanfeng Zhang,1 Allan R.
Mackintosh,2 Richard A. Pethrick,2 Erdan Gu,1 Nicolas Laurand,1 and Martin D.
Dawson1
1)
Institute of Photonics, SUPA, University of Strathclyde, Glasgow G4 0NW, UK
WestCHEM, Department of Pure and Applied Chemistry, University of Strathclyde,
Glasgow G1 1XL,UK
2)
a)
Author to whom correspondence should be addressed.
Electronic mail: yujie.chen@strath.ac.uk
[doi:10.1063/1.3659305]
Fig. S1 Flexible DFB substrate: (a) Photograph of the as-prepared CHDV substrate
showing light diffraction caused by the grating structure; (b) AFM image of the
replicated grating, and (c) profile of modulation depth corresponding to the line
marked in (b).
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Fig. S2 Photographs (taken under white light illumination from different angles)
showing light diffraction caused by the submicron grating structure on the substrate
surface. The scale bar represents 2 cm. in the plane of the substrate.
(a)
(b)
2 μm
2 μm
Fig. S3 SEM images of (a) blank DVD and (b) as-prepared CHDV substrate with
replicated submicron grating structure.
(a)
(b)
Fig. S4 Photographs of bending the flexible DVD-grating-patterned CHDV substrate:
(a) without and (b) with CQDs coated on the surface (illuminated by a UV lamp).
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He-Ne laser
(633 nm)
Flexible DFB
CQD sample
Fig. S5 Photograph of transmitted diffraction spots using a He-Ne laser (633 nm). The
1st order diffracted angle is around 50o that is in agreement with what the grating
equation predicted.
For lasing demonstration, a frequency-tripled Q-switched Nd:YAG laser
(wavelength 355 nm, pulse width 5 ns, and repetition rate 10 Hz) was applied to
photo-pump the CQD laser sample. A spherical lens was used to focus the pump
beam at about 45o to the sample surface, resulting in an excitation spot size of about
1.5 mm2 [see the pump spot profile in the inset of Fig. 1(a) in the main article]. For
spectral measurement, a fiber-coupled spectrometer having two channels with
respective spectral resolutions of 2.4 nm and 0.13 nm was aligned to collect emission
from the laser.
We have also studied the case when the substrate is bended (Fig. S6) through
analyzing the transformation of the grating structure. This is detailed below:
The period of the grating base and top is the same for a flat grating, Λ=Λ’.
When it is curved, the period of grating top will become larger than the base. From
Fig. S6, we have:
L'
L
NΛ ' N
R+h
h
= ⇒
= Λ ⇒ Λ' =
Λ = (1 + )Λ
R+h R
R+h R
R
R
(Eq. S1)
We bended our CQD sample to wrap around glass vials with different crosssection profiles with R in the range of 0.5 and 2 cm (and thus the corresponding
bending curvature is in the range of 2 and 0.5 cm-1). Considering the DFB laser
grating equation: mλem = 2neΛ’, given that h = 120 nm, the central lasing peak would
shift by only (h/R)λem < 0.02 nm and that is far below our spectrometer’s highest
resolution. It is therefore no surprise that we did not notice any wavelength shift when
bending the CQD laser sample. In other words, we do not have bending-induced
tunability in terms of lasing emission wavelength for our CQD DFB laser. This can
actually be beneficial for practical applications, since its lasing peak will not be
significantly changed when it is bent.
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(a)
(b)
Fig. S6 (a) Flat and (b) curved grating.
Fig. S7 (a) Polarization measurement on the CQD lasing behavior (pump fluence: 14
mJ/cm2; spectral resolution: 2.4 nm): (a) spectral evolution as the polarizer rotation
angle changes and (b) TE (o) and TM (90o) spectra with (inset) the polarization
intensity ratio of (ITE-ITM)/( ITE+ITM).
ACKNOWLEDGMENT
This work was financially supported by UK EPSRC under the HYPIX project.
Y. Chen appreciates the support from Scottish Universities Physics Alliance (SUPA).
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