In this study, we investigate  transient phenomena in synthetic diamonds  obtained by High Pressure High Temperature and  Chemical Vapor Deposition methods. Study was aimed at searching for inorganic crystalline media combining ionizing radiation detecting properties and non-linear absorption of ultra-short laser pulses. The nonlinear pump-and-probe optical absorption technique with of 140 fs laser pulses was used to study the effects

Barbarchik, E.

Buganov, O.

Fedorov, A.

Korjik, M.

Mechinsky, V.

Tamulaitis, G.

Tikhomirov, S.

Vietnam Academy of Science and Technology: Journals Online

Communications in Physics, Vol. 26, No. 3 (2016), pp. 253-259
DOI:10.15625/0868-3166/26/3/8957
TRANSIENT ABSORPTION PHENOMENA IN SYNTHETIC HPHT AND CVD
DIAMONDS FOR A FAST TIMING IN NUCLEAR INSTRUMENTATION
O. BUGANOV†, S. TIKHOMIROV AND E. BARBARCHIK
B. I. Stepanov Institute of Physics, 220072, Minsk, pr. 60 Nezavisimosti
M. KORJIK, A. FEDOROV AND V. MECHINSKY
Institute for Nuclear Problems of BSU, 220030, Minsk, 11 Bobruiskaya
G. TAMULAITIS
Vilnius University, LT-10222, Vilnius, Saultekio 9-III
†E-mail: o.buganov@ifanbel.bas-net.by
Received 05 December 2016
Accepted for publication 05 January 2017
Abstract. We investigate the transient absorption phenomena in synthetic diamonds obtained by
High Pressure High Temperature (HPHT) and Chemical Vapor Deposition (CVD) methods. The
aim of our study is to search inorganic crystalline media combining ionizing radiation and in-
vestigate their detecting properties and non-linear absorption of ultra-short laser pulses. The
pump-probe technique with 140 fs laser pulses was used for the investigations.
Keywords: two-photon absorption, synthetic diamonds, absorption. from excited states, fast tim-
ing.
Classification numbers: 05.45.Tp, 78.47.J-, 81.05.ug.
I. INTRODUCTION
Search of the processes which will form time marks with precision better than 10 ps and use
the interaction of ionizing radiation with detecting media is a crucial demand for the development
of a new generation of the detecting technique, especially in experimental particle and high energy
physics. Recently we suggest using the sub-picosecond phenomena occurring just after the inter-
action of scintillating material with ionizing radiation for temporal mark formation by probing the
material with ultra-short laser pulses [1–4].
c©2016 Vietnam Academy of Science and Technology
254 TRANSIENT ABSORPTION PHENOMENA IN SYNTHETIC HPHT AND CVD DIAMONDS ...
One of such phenomena is the elastic polarization due to the local lattice distortion caused
by the displacements of electrons and holes generated by the ionization. This local lattice distor-
tion results in redistribution of the density of states (DOS) of electron in the conduction band in
the vicinity of the hole. The key feature of the elastic polarization is its ultrashort response time,
which makes it prospective as an optically detectable time mark. Nonlinear optical absorption of
femtosecond light pulses at appropriate wavelengths is considered to be a tool to form time mark.
The effect of elastic polarization should be observed in many crystalline inorganic compounds.
According to our estimations, the strongest effect should be observed in compounds with the bot-
tom of the conduction band formed by nd orbitals of the lattice cations. In accordance with the
crystal field theory, these orbitals are most sensitive to distortions of the crystal field in the vicinity
of absorbing and emitting centers. Thus, the crystals with lattice cations having strong contribu-
tion of d orbitals in the conduction band (tungstates, molibdates, rare-earth and yttrium garnets,
perovskites, oxy-orthosilicates, etc.) might be good candidates for time markers.
We confirmed the influence of ionization at 122 keV on the two-photon two-color absorp-
tion of femtosecond laser pulses in PbWO4 crystals [1, 3]. The observed effect encouraged our
further study in this direction to develop a novel detecting technique exploiting the interaction of
ultrashort laser pulses with crystalline media excited by ionizing radiation.
In this study, we investigate transient absorption phenomena in synthetic diamonds ob-
tained by High Pressure High Temperature (HPHT) and Chemical Vapor Deposition (CVD) meth-
ods. Our study is to search inorganic crystalline media combining ionizing radiation and investi-
gate their detecting properties and non-linear absorption of ultra-short laser pulses. Accordingly,
we selected several diamond crystals suitable to detect ionizing radiation, particularly neutrons.
Synthetic diamonds are now considered as the most prospective materials to operate in a harsh
irradiation environment.
II. AN ADVANTAGE OF THE TWO-PHOTON ABSORPTION TO PROBE FAST
PROCESSES IN DETECTING MATERIALS
One-photon absorption is extensively used to monitor different effects in ionizing radiation
detectors. In fact, this technique enables monitoring slow changes in the detector material proper-
ties, particularly accumulation of the color centers under ionizing radiation. However, one-photon
absorption is not convenient to explore changes in the transient ionizing radiation induced effects
due to strong absorption of single photons via electronic transitions between valence and conduc-
tion bands. This is due to the origin of the bands of the majority of inorganic wide band gap
compounds: p electronic states form the top of valence band, whereas d and f states of metal ions
dominate in forming the bottom of the conduction band. Dipole-allowed p− d transitions result
in the absorption coefficient for the inter-band transitions at the order of 105cm−1.
The two-photon absorption coefficient is much less and intensity dependent. Consequently
it can be adjusted by choosing of laser beam intensity and the photons absorbed via two-photon
absorption propagate relatively long distances in the crystal. Two-photon absorption can involve
photons of the same frequency generated by the same laser or simultaneously available photons of
different frequencies [5]. The two-photon absorption involving one pump and one probe photon is
a convenient tool for studying both temporal and spectral parameters of the inter band absorption.
Recently, the pump-probe technique was exploited to study PbWO4 crystal [1, 3] which is the
most popular detecting material in High Energy Physics Experiments at LHC CERN Program.
O. BUGANOV et al. 255
The pump-induced changes in material properties resulting in modified probe absorption in the
sample volume where the pump and probe beams spatially overlap have been recorded. Our
measurements for 1-cm long samples showed that the change in optical density for the probe beam
induced by the pump at 395 nm has a short rise time, its decay with characteristic time constant
of few picoseconds, and a faster decay afterwards. The fast decrease of the induced absorption at
the middle of the response curve was explained by the separation of the pump and probe beams
in space, since the beams are focused on the same spot of the sample surface at slightly different
angles. The duration of the response curve in this region depends also on the pump and probe
wavelengths due to the dispersion of group light velocity.
III. EXPERIMENTAL RESULTS
Pump - probe setup was exploited in our study as described elsewhere [3, 6]. The 140 fs -
laser pulses of the second harmonic of Al2O3:Ti3+ laser was used to generate both the pump beam
at a fixed central wavelength of 395 nm (3.15 eV) and a white continuum ranging from 400 nm
to 1100 nm, which was generated in water by a fraction of the fundamental laser beam at 790 nm
and used as a probe. The diameters of the probe and pump spots within the sample were about 0.5
mm and 2 mm, respectively.
The spectra of the signal probe beam and the reference one were recorded for every laser
pulses by a polychromator equipped with silicon CCD matrix and transmitted to the computer.
The differential absorbance signal ∆D (λ ,∆t) is obtained as ∆D(λ ,∆t) = lg(T˜0/T˜ ), where T˜ =
Eprob/Ere f and T˜0 = E0prob/E
0
re f are energy ratios of the probe and reference pulses passed through
the investigated sample at excitation and without it respectively. Typically, 30 measurements were
averaged to give a wavelength-dependent signal at every time step. The transient absorption spec-
tra are recorded in the range of 400 nm –800 nm with a resolution of 1.5 nm. The estimated
absolute error for ∆D was as about 0.001. The transient spectra were corrected for the group
velocity dispersion of the probe pulse
Two High Pressure High Temperature (HPHT) diamond samples were produced by
ADAMAS-BSU, Minsk, Belarus. The sample dimensions are 4× 4× 0.3 mm. The samples
had yellow coloration due to the presence of nitrogen. The cutoff of the transmission spectrum of
both samples was found to be near 420 nm. One of the samples was found to be scintillating, and
another to be not scintillating. The Chemical Vapor Deposition (CVD) diamond with dimensions
of 4×2×0.15 mm was provided by CERN.
In contrary to the PbWO4 complex oxide crystal based on oxy-anionic complexes, diamond
is a wide band gap indirect semiconductor having a relatively simple electronic band structure due
to its monoatomic network. Two-photon absorption in nitrogen-free diamond was investigated in
detail [7]. The lowest two-photon absorption band was observed to a peak at the total two-photon
energy of 5.5 eV. This energy corresponds to the indirect transition to conduction band. The direct
two-photon absorption was found to occur at 6.5 eV.
We observed two-photon absorption effects in all diamond samples under the study. Figures
1, 2 and 3 show our obtained results. The most important feature for the response of all studied
samples is that the leading edge of the differential absorption is limited by laser pulse shape rather
than by material properties. Thus, the processes responsible for the nonlinear absorption occur on
femtosecond time domain.
256 TRANSIENT ABSORPTION PHENOMENA IN SYNTHETIC HPHT AND CVD DIAMONDS ...
-2 0 2 4 6 8 10 12 14
0,000
0,005
0,010
0,015
0,020
0,025
0,030

D
t, ps
 465 nm
 720 nm
 
 
 
 
 
 
 
 
400 450 500 550 600 650 700 750
0,00
0,01
0,02
0,03

D
, nm
     t, ps
1: -1,0
2:  0,3
3:  0,6
4:  1,0
5:  15
1
2
3
4
5
a) 
b) 
Fig. 1. a) Spectrum of differential absorption of the no-scintillating diamond sample at
395 nm pump at different delays between pump and probe (indicated); b) Kinetics of
differential absorption of the no-scintillating diamond sample at 395 nm pump and two
probe wavelengths: 465 nm and 720 nm.
O. BUGANOV et al. 257
400 450 500 550 600 650 700 750
-0,02
0,00
0,02
0,04
0,06
0,08
0,10      t, ps
1: -1,0
2:  0,0
3:  0,6
4:  8,0
5:  15,0
, nm

D
1
2
3
4
5
-2 0 2 4 6 8 10 12 14 16
-0,02
0,00
0,02
0,04
0,06
0,08

D
t, ps
 445 nm
 700 nm
 
 
 
 
 
 
 
 
a) 
b) 
Fig. 2. a) Spectrum of differential absorption of the scintillating diamond sample at
395 nm pump at different delays between pump and probe (indicated); b) Kinetics of dif-
ferential absorption of the scintillating diamond sample at 395 nm pump and two probe
wavelengths: 465 nm and 720 nm.
258 TRANSIENT ABSORPTION PHENOMENA IN SYNTHETIC HPHT AND CVD DIAMONDS ...
400 450 500 550 600 650 700 750
0,00
0,02
0,04
0,06

D
, nm
     t, ps
1: -1,0
2:  0,0
3:  0,5
4:  2,0
5: 15,0
1
2
3
4
5
-5 0 5 10 15 20
-0,01
0,00
0,01
0,02
0,03
0,04
0,05
0,06

D
t, ps
, nm
 435
 720
 
 
 
 
 
 
 
 
 
 
a) 
b) 
Fig. 3. a) Spectrum of differential absorption of the CVD diamond sample at 264 nm
pump at different delays between pump and probe (indicated); b) Kinetics of differential
absorption of scintillating diamond sample at 263 nm pump and two probe wavelengths:
435 nm and 720 nm.
The band peaked at ∼ 465 nm (2.6 eV) correlates fairly well with the energy of the indirect
two-photon two-color transition (one photon from pump pulse and other – from probe) to the
conduction band. Other bands observed in the samples are peaked within 550 – 600 nm and at
∼700 nm. All induced absorption bands decay fast within the first picoseconds and have also a
slow decay component. The total energy of pump and probe photons for the 550 – 600 nm and
O. BUGANOV et al. 259
700 nm bands are considerably smaller than band gap of diamond, so we can conclude that defect
centers are mainly responsible for the transient absorption in this spectral region.
It should be noted that when the scintillating diamond sample is probed at 700 nm, the
kinetics of transient absorption (Fig. 2) is differ from that of the no-scintillating sample (Fig. 1).
There are two risen processes: the fast process, less than one picosecond, is dedicated to direct
excitation of defects by two-photon or one- photon transitions and the slow process lasts a few ps,
which to our mind, is due to a population of the defects by capturing the carriers from conduction
zone.
On the contrary to the HPHT diamond samples, the CVD diamond did not show any spectra
of differential absorption at 395 nm pump. Strong differential absorption was found only at pump
264 nm. We observed a strong band in the blue range peaked at 430 nm and also two weak bands
roughly peaked at∼550 nm and 700 nm (Fig. 3). So, one can state that two last bands related with
the defects and that concentration of defect centers in the HPHT diamonds is considerably larger
than that in the CVD diamond.
The difference in transient absorption decay is observed for the CVD diamond with the
probe at 435 nm and 720 nm as seen in Figure 3 (b). Due to small concentration of defects the
signal is relatively weak with the probe at 720 nm but has an increasing tendency toward the IR
region.
IV. CONCLUSION
The observed nonlinear optical effects might be exploited for timing of the interaction of
diamond detector materials with ionizing radiation by one-photon absorption or by two-photon
absorption methods. Two-photon two-color absorption has the advantages in sensitivity, time
resolution, and simplicity of signal interpretation.
ACKNOWLEDGEMENT
The partial financial support from Belarusian Republican Foundation for Fundamental Re-
search (Project F16-011/1, Project F16V2-003) and MSC INTELUM project are appreciated.
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Transient Absorption Phenomena in Synthetic HPHT and CVD Diamonds for a Fast Timing in Nuclear Instrumentation

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Transient Absorption Phenomena in Synthetic HPHT and CVD Diamonds for a Fast Timing in Nuclear Instrumentation

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