Some new experimental photonic flame effect features
PHOTONIC FLAME EFFECT
SOME NEW  EXPERIMENTAL PHOTONIC FLAME EFFECT 
FEATURES  
N.V.Tcherniega 
P.N.Lebedev Physical Institute, RAS 
Leninskii pr., 53, 119991, Moscow, Russia 
tchera@sci.lebedev.ru
Abstract 
     The results of the spectral, energetical and temporal characteristics of radiation in the 
presence of the photonic flame effect are presented. Artificial opal posed on Cu plate at the 
temperature of liquid nitrogen boiling point (77 K) being irradiated by nanosecond ruby laser 
pulse produces long- term luminiscence with a duration till ten seconds with a finely structured 
spectrum in the the antistocks part of the spectrum. Analogous visible luminescence manifesting 
time delay appeared in other samples of the artificial opals posed on the same plate. In the case 
of the opal infiltrated with different nonlinear liquids the threshold of the luminiscence is 
reduced and the spatial disribution of the bright emmiting area on the opal surface is being 
changed. In the case of the putting the frozen nonlinear liquids on the Cu plate long-term blue 
bright luminiscence took place in the frozen species of the liquids. Temporal characteristics of 
this luminiscence are nearly the same as in opal matrixes.  
Keywords: photonic flame effect, optical luminescence, excitation, artificial opal, spectrum 
1. Introduction 
    In [1-3] new effect called photonic flame effect was found and some its properties were 
studied. This effect is determined by  properties of photonic crystals.       
    Photonic crystals have attracted great attention since the first papers concerning such 
structures [4-6]. One of the most important photonic crystals are artificial opals – self –
assembled structures composed of SiO2 spheres organizing face-centered cubic lattice. The size 
of such spheres varying between 200 nm and 400 nm and defines the parameters of the face-
centered cubic lattice and the photonic bandgap. The possibility of opal infiltration with different 
medium gives rise to effective processing the properties of the light propogating through the 
crystal. The voids in the opal structures can be filled with semiconductors, superconductors, 
ferromagnetic materials, fluorescent medium [7] and this fact gives large possibility to practical 
applications of such structures for optoelectronics.  The study of the linear optical properties of 
the photonic band gap have been the task of many theoretical and experimental works and still 
remain the task to be investigated [7,8]. The theoretical description of the electromagnetic field 
inside the photonic crystal structures (obtained by transfer matrix method [9] or coupled mode 
theory [10]) gives the clear picture of the transmitted and reflected spectrum, electromagnetic 
field distribution inside the crystal and their dependence on the parameters of the photonic 
crystal structure (values of period, number of periods, refractive index contrast). Large values of 
the electromagnetic field localization in some regions lead to the expectation of the strong 
enhancement of nonlinear wave-matter interaction in comparison with bulk crystals. Second 
harmonic generation in different types of photonic crystals was investigated in [11,12]. Properly 
chosen photonic crystal exhibits negative refraction at some conditions [13]. Some features of 
the stimulated Raman scattering in one-dimensional photonic structure  were considered in [14]. 
Fully quantum mechanical treatment of the generation of entangled photon in nonlinear photonic 
crystals at the process of down-conversion was realized in [15]. Photonic band gap properties 
which are demonstrated by  photonic crystalls are being actively used for investigation of 
photon-exciton interaction [16]. Acoustic modes excited in SiO2 balls which compose opal 
photonic crystal show the effect of phonon modes quantization [17] and are the reason of 
stimulated globular scattering [3]. Specific features of the acoustic wave propagation in the 
photonic structures lead to the possibility of the diverging ultrasonic beam focusing into a 
mailto:tchera@mail1.lebedev.ru
narrow focal spot with a large focal depth [18]. Optical parametric oscillations via four-wave 
mixing in isotropic photonic crystals showes the possibility of the effective frequency processing 
[19].  
    The aim of this work is to give a short review of results [1-3] and to  study collective behavior 
of several photonic crystals. The crystals are posed on Cu plate at the temperature of liquid 
nitrogen. One of the photonic crystals is illuminated by laser pulse and the laser light is focused 
on this only crystal. The phenomenon which we observe is the appearance of  luminescence of  
other photonic crystals. The duration of the luminescence of other crystals which are spatially 
separated with the crystal illuminated by laser pulse is of the order of seconds. The appearance of 
the luminescence takes place with some time delay respectively to the laser pulse. The form of 
these  light spots on the other crystals and their slow motions along the crystal reminds a small 
flame spot. This inspired us to give the “photonic flame” name to the observed effect. In the case 
of covering the surface of the Cu plate with liquid (acetone, ethanol, water) after the PFE 
excitation in the opal situated on this plate  blue luminescence is being seen in the frozen liquid. 
The temporal characteristics of this luminescence are the sme as for single opal crystal. The 
paper is organized as follows. In Sec.2 the experimental setup, laser, the photonic crystals 
(artificial opals) used in the experiment are described. In Sec.3 the “photonic flame effect” 
observed in the experiment is discussed. In Sec.4 perspectives and possible explanations are 
presented.    
2. Photonic crystals and laser used in experiment. 
    One of the most promising three-dimensional photonic crystals is artificial opal. Opal is a 
crystal with face-centered cubic lattice consisting of the monodisperse close packed SiO2 spheres 
with diameter about several hundred nanometers. Because the refractive index contrast (ratio 
nSiO2/nair) is about 1,45 the complete photonic band gap does not exist but the photonic 
pseudogap takes place. Empty cavities among these globules have octahedral and tetrahedral 
form. It is possible to investigate both initial opals (opal matrices) and nanocomposites, in which 
cavities are filled with organic or inorganic materials, for instance, semiconductors, 
superconductors, ferromagnetic substances, dielectrics, displaying different types of  
Fig.1.  Common appearance of a globular photonic crystal, built of spherical particles (globules)  
nonlinearities and so on. Filling voids of the photonic crystal with materials with different 
refraction index one can effectively process the parameters of the photonic pseudogap. 
 Ruby laser giant pulse (λ=694.3 nm, τ=20 ns, Emax =0.3 J, spectral width of the initial light - 
0.015 cm-1.) has been used as a source of excitation. Exciting light has been focused on the 
material by lenses with different focal lengths (50, 90, and 150 mm). The samples of opal 
crystals used had the size 3x5x5mm and were cut parallel to the plane (111) (see Fig.2) .The 
angle of the incidence of the laser beam on the plane (111)  varied from 0 to 600. Sample 
distance from focusing system and exciting light energy were different in different runs of the 
experiment. This gave possibility to make measurements for different power density at the 
entrance of the sample and for different field distribution inside the sample. Opal crystals 
consisting of the close-packed amorphose spheres with diameter 200 nm, 230 nm, 250 nm and 
nanocomposites (opal crystals with voids filled with acetone or ethanol) were investigated.   
                                                                                       z
                                           θ                                                                        y
                                                                  [111]                                 x
Fig.2. The scheme of  illuminating the sample. Plane XY correspondes to the CU plate surface. 
3.Characteristics of “photonic flame” 
     Opal crystals were placed on the Cu plate which was put into the cell with liquid nitrogen (see 
Fig.3). The number of crystals varied from 1 to 5. The distance (d) betwen the crystals was of the 
order of several centimeters (maximum value of d was 5 centimeters and was determined by the 
Cu plate size).  One of the crystals was illuminated by the focused laser pulse. In the case of the 
reaching of the threshold visible (blue) luminescence appeared. The luminescence duration was 
from 1 to 12 seconds and it looked like inhomogeneous spot changing its spatial distribution and 
position on the surface of the crystal during this time.    
                                                           liquid   N2
                                                                 opal               opal
                                                                                                               exciting light
                                                      d
                                   opal                 Cu
Fig.3. Experimental setup. 
    Parameters of the luminescence (duration, threshold) were determined by the geometric 
characteristic of the illumination and the refractive index contrast of the sample. For optimal 
geometry of the excitation the power density threshold for opal crystal was 0.12 Gw/cm2, for 
opal crystals filled with ethanol – 0.05 Gw/cm2, for opal crystal filled with acetone - 0,03 
Gw/cm2. Typical luminescence temporal distribution measured for the part of the crystal 
displaying the most intensive brightness is shown on Fig.4. The same behavior is typical for all 
cases of the luminescence at these conditions of excitation, but the value of the luminescence 
duration fluctuated from shoot to shoot. 
                                  a)                                                              b) 
Fig.4. Temporal distribution of the visible luminiscence.  
     The duration of the luminiscence fluctuated from 1 till 12 seconds and demonstrated 
oscillating structure. In some cases the temporal distribution had maximum at the beginning of 
the luminiscence in some cases – minimum. Fig.4 a) and b) show the luminiscence of the pure 
opal matrix of the nearly the same duration at the same geometrical and energetical conditions of 
excitation near the threshold of excitation (0.12 Gw/cm2 ). The beginning of the mesurements 
corresponds to 0.3 s delay after the laser shoot  (laser pulse duration is 20 ns).  
     Secondary emission spectrum observed in photonic flame effect has been investigated with 
the help of setup shown at the Fig.5. 
                             
                                          12
                          11                                          10
                                                      9
                                          8
                                                                                1
                    3                4          2
             6           7
    Fig. 5.The experimental setup for PPE spectrum study. 1- ruby laser; 2- lens; 3, 4, 5 – photonic 
crystals; 7 – cell with liquid nitrogen 6 – Cu plate; 8 – fiber wave guide; 9 – minipolychromator; 
10 – computer; 11 – camera; 12 – computer. 
Spectra of the light emitted by photonic crystal  for different pumping light power density are 
shown at the Fig. 6  (a and b) 
                                                                                                                   
200 300 400 500 600 700 800 900 1000
643I, 
λ, nm
200 300 400 500 600 700 800 900 1000 1100
λ, nm
                              a                                                          b                                           
 Fig. 6. Secondary emission spectrum of a photonic crystal for different laser light power density: 
a - I = 0.12 GW/cm2,     b - I = 0.14   GW/cm2. 
Spectrum consisted of the sharp lines with wavelengths: 429.0, 453.0, 489.0, 555.0, 643.0 nm, 
which corresponds to the antistokes spectral range for exciting line 694.3 nm. Lines intensity in 
the spectrum strongly depended on the laser pumping intensity, which was evidence of 
stimulated type of the radiation emission.  
    In the case of several crystals placed on  the Cu plate only one of them was irradiated by the 
laser pulse. Luminescence took place in this crystal in the case of the threshold reaching. Bright 
shining of the other crystals began with some time delay after laser shoot. The value of this delay 
(and the intensity of the luminiscence) was determined by the spatial position of the crystals on 
the plate. The steal screen beeing put between the crystals (in order to avoid irradiating of the 
crystals by the light scattered by the crystal excited by the laser) did not stop the appearing of the 
luminescence if the distance between the Cu plate and the screen was more than 0.5 mm.  The 
duration of the luminiscence was of the order of several seconds and temporal behavior was like 
shown on Fig.4. The typical features of such distribution were existence of  maximum and large 
plato with near constant value of the intensity. 
     In order to show the role of the material of the plate used we repeated these measurements 
with plates of the same size but made from steel and quarz on which opal crystals were placed 
like in the previous experiments. Luminescence of the same kind in the irradiated crystal took 
place but the luminescence of the other samples situated on these plates was not observed.   
    The effect was also determined by the angle of incidence (Fig.2). For the samples used the 
value of the angle was chosen experimentally for achieving of the maximal value of the 
luminescence (it worth to mention that this value differed from 0 and was about 400). Easier the 
effect was excited in the unprocessed samples. In Fig.5 one can see the luminescence of the 
crystals situated at the distance of about 1 centimeter from the crystal which was irradiated. 
                                 
Fig.7 Visible luminiscence of the opal crystals in the case of the irradiating one of them (the 
irradiated crystal can be seen by bright red light; on the left picture it was the crystal in the 
center, on the right picture  it was the crystal on the left). Left picture corresponds to the case 
where crystals are infiltrated by acetone. Right picture corresponds to the case of the opal 
crystals without infiltration. 
       In the case of the large laser energy (several times more the threshold) or if the crystal was 
irradiated by several laser pulses the opal can be destroyed and the parts of the crystal produce 
the luminiscence with the spectral  and temporal properties described above (Fig.8). 
Fig.8 Opal crystal is destroyed and 3 large pieces and several little pieces are going on to 
produce the luminescence. 
      In order to clarify the role of the Cu plate surface on the energy transport between the 
crystals the next experiment  was realized: the pure opal matrix posed on the Cu plate was 
irradiated  by the ruby laser pulse and demonstrated strong luminescence lasting few seconds 
with the properties described above (Fig.9)  
Fig.9  Luminiscence of the single opal matrix 
    Next step was covering the surface of the Cu plate with the liquid (experiments were made 
with water, aceton or ethanol). The thickness of the frozen liquid on the plate surface was about 
1 mm. The transverse size of the frozen liquid was about 1 cm. After illuminating of the crystal 
by the ruby laser pulse the luminiscence of the crystal appears the bright blue luminiscence of 
the frozen species of the liquid used appears. The temporal characteristics of the luminiscence in 
crystal and in the frozen liquid are approximatly the same (the luminiscence duration is about 
several seconds). The luminiscence of the frozen liquid goes on in spite on the putting the screen 
between the crystal and the liquid. It shows that the luminiscence of the liquid is not a reflection 
of the light which is emmited by the crystal. Fig.10 shows the luminiscence of the crystal and the 
frozen liquid (in this case it was water). The pictures were made with the interval of 1 second 
between each other. Analogous behaviour is demonstrated by aceton and ethanol. The 
luminiscence of the area covered with frozen liquid takes place even if this area is at the distance 
of several cantimeters from the irradiated crystal.The explanation of the blue luminiscence of the 
frozen liquid can be done in several ways and for clarifying the reasons of this luminescence 
appearance it is necessary to produce additional experiments.  The intensity of the laser in the 
experiments is about 0.12 Gw/cm2, and the large enhancement of this field due to Mie – 
resonance [20]  simultaniously with the interference effect caused by the structure of the opal 
matrix can lead to the extremely large field enhancement which can play an important role in this 
effect.  
                                                                                                                   
                                                                                                                                                                          
Fig.10  Luminiscence of the opal matrix (bright round spot) and frozen liquid (large blue spot) 
on the surface of the Cu plate.  
   4. Conclusions. 
   In this paper we reported about some new features of the photonic flame effect. The main 
features of PFE are: 
- At the excitation of the artificial opal crystal which is placed on the Cu plate at the 
temperature of the liquid nitrogen by the ruby laser pulse of the nanosecond range long-
continued optical luminescence takes place in the case if the threshold of the process        is 
reached;                                                                                               
- In the case of  several opal crystals being put on the Cu plate while one of them is being          
irradiated bright visible luminescence occurs in all samples;                               
- Temporal behavior and thresholds of the luminescence have been determined. Photonic    
crystals infiltrated with different nonlinear liquids and without infiltration have been 
investigated. Investigated transport of the excitation between the samples spatially separated 
by the length of several centimeters gives the possibility of the practical applications of  
PFE; 
- The blue luminiscence of the frozen liquid on the surface of the Cu plate takes place at the 
precense of the photonic flame effect; 
   The photonic flame effect can have different explanation. Probably an essential role is played 
by plasma properties. The slow transport of the excitations from the irradiated crystal to other 
photonic crystals can be associated with sound waves created due to laser pulse interaction with 
the sample. Exciton mechanism and surface waveguides on the surface of the Cu plate also can 
play important role. It was checked that the change of the properties of the plate surface was 
leading to change of the photonic flame effect. Removing the oxid layer from the plate changed 
the threshold PFE. The luminescence of the frozen liquids on the surface of the Cu plate showes 
the important role of the electromagnetic field enhancement due to Mie resonance and Bragg 
diffraction on the photonic crystal lattice. The electromagnetic field enhancement  can lead to 
producing laser plasma, electron acceleration and x-ray production.    
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