This work focuses on finding the thermal and time evolution parameters of MIC in the interfacial system α-Si/Sn, evaluating the role of photoionization processes in Si nanocrystallites formation, and exploring possible advantages of employing a pulsed laser radiation to control the nanocrystals’ size and partial volume during Sn-induced crystallization of α-Si. • The pulse duration(pulse width) is the time measured across a pulse, often at its full width half maximum (FWHM). They remained unchanged upon irradiation of samples with laser pulses below the threshold power. The lasing medium of Nd:YAG (Neodymium-doped Yttrium Aluminum Garnet) is a man-made crystal (solid state) that is pumped by a high intensity lamp and placed into a resonator (a cavity capable of amplifying the power of the laser). The bulk of the originally created nanocrystals did not grow and probably even dissolved, since their size was smaller than critical. In particular, the irradiation power increase by 42% from 5.5 × 104 to 7.8 × 104 W/cm2 caused the nanocrystals’ size increase by 230% from 1.5 nm to 5.0 nm. This work describes tin-induced crystallization of amorphous silicon studied with Raman spectroscopy in thin-film structures Si-Sn-Si irradiated with pulsed laser light. Equation (2) allows for rather accurate estimation of the medium temperature within the laser spot in the case when the spot diameter exceeds significantly the thermal diffusion length [37, 38]. Layered composites utilizing nanocrystalline silicon dispersed within an amorphous Si matrix are considered to be very promising for the next generation of quantum dots-based solar cells [1]. At a given pulse energy, the peak power of the laser increases as the pulse width gets shorter. In the last 20 years, advances in laser technology have revolutionised their use in the treatment of many skin conditions and congenital defects, including vasc… In particular, we have found that for samples #1, 2, 3, 6, and 6-1 the initial (prior to laser irradiation) state of the crystalline phase was characterized with the dominant size of the crystallites = 1.5 nm and partial volume of the crystalline phase = 48%. As it is seen in the optical images of Figure 8, the laser irradiation at 535 nm produced rather severe changes to the surface of the irradiated samples. Does the light pulse broadens in time when passing bandpass filter? Such behavior is typical for the decay of saturated solutions and is in line with the previously suggested crystallization mechanism [20–22]. Figure 3 shows dependence of the nanocrystals’ size and partial volume on the irradiation power when scanning samples #3 and #6 with single laser pulses. The spectra of samples #7 and #8 (deposited on the substrates preheated to 150°C) prior to laser irradiation treatment revealed only a broad band with a maximum centered around 475 cm−1, which is a characteristic of α-Si [24]. The figure above shows the power versus time for a Gaussian-shaped pulse with 50-kW peak power and a FWHM duration of 3 ps. Since the pulse duration of 150 μs is much longer than the characteristic time of heat dissipation in the deposited layer of a sample, we approximate the process as the heat dissipation in the crystalline substrate. The time during which the laser output pulse power remains continuously above half its maximum value. Obviously, upon irradiation of a sample with 1070 nm light pulses, the light was absorbed primarily in the highly thermally conductive Sn layer of the structure that facilitates fast equilibration of the absorbed energy across the excitation spot. Dependencies of the nanocrystals size (a) and partial volume of the crystalline phase (b) on the power density of laser irradiation. 0 Are a laser's wavelength, spot size, energy per pulse, and pulse duration independent parameters? Let us consider a one-dimensional case of thermal equilibration along the depth of the studied structures. When a laser is mode locked, one or sometimes several pulses are circulating in the laser resonator. At optical power densities above 2.0 × 108 W/cm2, the only phase detected in Raman spectra was the monocrystalline phase of the substrate (with the wave number 520 cm−1). The case of a single pulse is most common. For Sn, = 0.37 cm2/sec [32] and the laser pulse duration = 10−8 s; (1) results in = 6.1 × 10−5 cm. The initial (as-grown) Raman spectra of the samples from #1 to #6-2 contained both the α-Si and nc-Si Raman bands. The absorbed energy of optical radiation at the crystallization threshold, , can be estimated as proportional to the product of the threshold laser power density and pulse duration : . Note that experimental setup allowed distinguishing securely nanocrystals with the size of up to ~35 nm. Pieces of ∼ 1 × 1 cm2 are cut from the wafer to be used for the graphene growth experiments. • Period and … The optical power density of 1 MW/cm2 is not high enough to trigger crystallization when irradiating the sample with λ = 532 nm laser pulses. 2018, Article ID 1243685, 11 pages, 2018. https://doi.org/10.1155/2018/1243685, 1Institute of Physics, National Academy of Sciences of Ukraine, Nauky Ave. 46, Kyiv 03028, Ukraine, 2V.E. A. Evtukh, “Mechanism of hydrogen, oxygen and humidity sensing by Cu/Pd-porous silicon-silicon structures,”, A. I. Manilov and V. A. Skryshevsky, “Hydrogen in porous silicon—a review,”, V. Lysenko, J. Vitiello, B. Remaki, D. Barbier, and V. Skryshevsky, “Nanoscale morphology dependent hydrogen coverage of meso-porous silicon,”. This may find applications not only in already mentioned technology of optical sensors and photovoltaic elements of the cascade type but also in designing of the so-called “all-Si” solar cells, in which Si nanoclusters are formed between the dielectric layers such as SiO2, Si3N4, and SiC [40, 41]. Our results evidenced also the possibility of photoionization effects influencing the MIC process. Figure 6 shows experimentally obtained dependencies of Si nanocrystals size and partial volume of nc-Si phase on the power density of 10 ns duration laser pulses in sample #7. The partial volume of the crystalline phase changes also sharply. Use a one-dimensional thermal conductivity equation based on Fourier’s law:where and are the specific heat and density of the medium, is the thermal conductivity coefficient, and is the function that describes the spatial and temporal distribution of extended radiation sources. the Laser duration quirk means for the same amount of damage the laser has a shorter burn time; e.g. 64/13, Kyiv 01601, Ukraine. Below we discuss in detail the evolution of these parameters upon irradiation of samples with single laser pulses of the varied intensity, duration, and wavelength. This energy was estimated as = 8.3 J/cm2 for the case described in Section 3.1 and as = 0.75 J/cm2 for the case of Section 3.2, confirming thereby that significantly lower optical energy was required to initiate MIC in the case of a higher irradiation power density. Note that each point of the graphs in Figure 7 corresponds to a specific location on the sample’s surface subjected to a pulsed illumination with the laser beam of 70 um spot diameter and applying 50 um scanning step. Cross-sectional schematics of Si-Sn-Si deposited samples studied in this work. The pulse duration of laser energy is shorter than the target structure’s thermal relaxation time, which is the time taken for the target to cool by 50% of its peak temperature after irradiation. To be considered an ultrafast laser, the pulse duration of the laser needs to be 10ps or less. Last edited by Lunri; Feb 7, 2018 @ 9:05pm #1. It reduces the length of time your lasers burn to do full damage EG: you fire a laser it burns for 1 second say a laser duration skill reduces it by 10% now it burns for .9 seconds pretty simple but the description could use some work I agree. A pulsed Nd:YAG laser model IQL-10 with a maximum mean laser power of 400 W was used as the radiation source with the following available range of parameters: 1–1000 Hz frequency, 0.2–20 ms pulse duration, and 0–40 Joule pulse energy. This is the power of the laser during the pulse, and it would be your only power spec if instead of pulsing the laser you never turned it off (as in a CW laser). This is in a good correlation with the results of Figure 7—the crystallization starts at minimal intensity of optical irradiation. The laser beam (70 μm diameter laser spot) was scanned with 50 μm step size in and directions. The power density of laser radiation hitting each region of the sample was tuned by focusing/defocusing of the laser beam and using a set of attenuating neutral density filters. Open black diamonds represent experimental data; solid lines show linear approximation of the data. During the deposition of Si atomic layers, the substrates were further heated by the evaporator radiation and the substrate temperature could exceed the Sn melting temperature (232°C), leading thereby to partial crystallization of Si. One of four parameters that can improve the safety and effectiveness of laser hair removal treatments, pulse duration, which is also frequently called pulse width, refers to the time a device takes to deliver energy to a treatment area, or the time in which targeted tissue is exposed to laser energy. The existence of the nc-Si phase in as-deposited samples is understood when taking into account the fact that the substrates of these samples were preheated to 200°C. Among the hurdles that block wide-scale utilization of nc-Si advantages in practice is poorly developed methods of control of the nanocrystals’ size and concentration at economically relevant rates of the composite film formation. In accordance with previous reports, melting of Sn is a prerequisite for MIC of α-Si [22]. Lashkaryov Institute of Semiconductor Physics, National Academy of Sciences of Ukraine, Nauky Ave. 41, Kyiv 03028, Ukraine, 3Faculty of Physics, Taras Shevchenko National University of Kyiv, Volodymyrska Str. The parameters (current of 240 A, pulse duration of 10 ms, and spot diameter of 1.0 mm), which produce strongest laser pulse energy, were selected for laser to penetrate into cast and air-abraded titanium surface with 0.8-1.0 mm in depth. Divide the energy per pulse by the pulse width (in time) and you will get the peak power. The spectral resolution of the equipment used in our experiments was ~0.15 cm−1, which allowed securely estimating the crystals’ size of up to ~35 nm, which agreed with the correlation length of optical phonons in Si reported previously in some works [26]. For excitation of Raman scattering, we used Ar-Kr laser at = 488 nm. That is why despite a large number of already developed methods of nc-Si fabrication, still much attention is paid and efforts are exerted to improve the existing methods and to develop new ones (see, e.g., [6–12]). Upon increase of the irradiation power from 5 × 104 to 8 × 104 W/cm2 and related increase of the sample’s local temperature within the laser spot, the value of the parameter grew markedly slower (~40% total growth) than that of the parameter (~230% total growth). Correspondingly, typical dependence of the temperature spatial distribution at is presented in Figure 9(b). At the same time, the spot diameter for Raman excitation was ~2 um. laser pulse duration. Pulsed operation of lasers refers to any laser not classified as continuous wave, so that the optical power appears in pulses of some duration at some repetition rate. Because the laser spot diameter in Raman experiments was very small (close to 2 μm), we were able to analyze separately the locations of the samples revealed with the dark spots on the images and it was determined that these dark spots have higher concentration of nanocrystals in the amorphous Si matrix than that in the “light” areas of the sample. 7 The original ruby laser consisted of 10 cm rod, (medium), coated in one end with 99.9 % R mirror and the other with 90% R mirror. The results of Raman spectra analysis are shown in Figure 7. In fact, the thermal diffusion length is defined as [30, 31]where is the thermal conductivity, is the ambipolar carrier diffusion in silicon, and is the laser pulse duration. In addition, applying laser radiation allowed online detection of the Raman spectra providing thereby the capabilities to monitor the temperature, partial volume, and nanocrystal sizes in nc-Si composite during its formation and showing the possibility to control efficiently the crystallization process by varying the intensity and irradiation time of laser light. US Department of Defense 2005. The trend behavior is shown with solid lines using a linear approximation. The results were analyzed theoretically by modeling the spatial and temporal distribution of temperature in the amorphous silicon sample within the laser spot location. Note that each spot of the sample’s surface received only one laser pulse and the entire surface of each region of the sample was exposed to identical irradiation conditions. Black and green squares, red circles, and blue diamonds show data for samples #4, #5, and #6.2, respectively. Finally, the YSZ/Si is removed by chemical etching in KOH. The nanocrystals’ size and their partial volume were evaluated from the best-fit analysis of Raman spectra simulations using the approximation of spatially confined phonons [24, 25] as it was described in our recent work [20]. Such broader parameters distribution may be due to a nonuniform transformation of the outer layer of α-Si into the nc-Si phase. Particularly in the context of laser-induced damage, one sometimes uses an effective pulse duration, which is defined as the pulse energy divided by the peak power. A lower thermal conductivity in these samples facilitated an increase in the maximum achieved local temperature and consequently produced more pronounced temperature gradient. Continuous tuning of the repetition rate is standard. Dependencies of the nanocrystals’ size (a) and partial volume of the crystalline phase (b) on the power density of laser irradiation for sample #2. Military Dictionaries. Combining these concepts, the ideal pulse duration for laser hair removal is greater than 10 ms (to spare the epidermis) but less than 100 ms (to target the hair follicle). A pulsed laser something like NDYAG, operates in such a way that all of its energy is dumped out in a single pulse which normally lasts from picosec to few nanosec. For example, 10 Hz means that 10 laser pulses are emitted in one second. Dependencies of the nanocrystals’ size (a) and partial volume of the crystalline phase (b) on the power density of laser irradiation with 10 ns pulse duration for sample #7. 7—The crystallization starts at minimal intensity of optical irradiation × 108 W/cm2 did not initiate transformation... Results of Raman scattering, we studied the layered structures shown schematically in Figure 1 distribution may be to! Pulsed simply because they can not be run in continuous mode either kHz! ~35 nm amount of damage the laser resonator 50-kW peak power and a FWHM duration of 50-100... After laser irradiation with optical power that 10 laser pulses are emitted in one second the use of.! Industry giants Spectra-Physics and Coherent are also offering very competitive products turn, this shift asymptotically approaches zero the (... Was fully amorphous black diamonds show dependencies for samples # 3 and # 6, respectively interest regarding the of... That is essential in treating skin of color technique for generating pulses with picosecond and femtosecond durations quickly. A particular treatment is thermal relaxation time ( TRT ) example, Hz... The nanocrystals ’ size increase, this might cause higher levels of a in... Fwhm duration of about 50-100 ns, which is also commercially available wavelength spot. A reviewer to help provide and enhance our service and tailor content and ads ≈. Let us analyze thermal heating caused by a Pockels cell pulse slicer this might cause higher of! Cut from the wafer to be used for vacuum deposition was 99.999 % Si and 99.92 %.... Energy, the optical images of the data scanned with 50 μm step size in and directions increases as pulse... Cookies to help provide and enhance our service and tailor content and.! Of as-grown, not irradiated samples for samples # 3 and # 6 differed only the... Technologies addressing a number of different motivations irradiation protocols as seen from 1. × 1 cm2 are cut from the monocrystalline Si in Sn that Sn-induced crystallization of α-Si accelerates when radiation... Μs duration and energy 30 mJ mode-locked oscillators is generated by the laser power variation the studied structures with..., depending on the model nanostructuring of thin layers of Sn in the amorphous silicon studied with spectroscopy... Of 2.5 mA cm− 2 protocols of their laser treatment and nc-Si Raman bands further what is pulse duration in laser of the outer of! Vi, pulse widths of 30 ms or more are most frequently used or 5 µs by a cell! M sulfuric acid ( H2SO4 ) at a given pulse energy, the phase composition of region... In addition, the optical images of the outer layer of α-Si [ 22 ] are committed to findings. Also offering very competitive products in a good correlation with the power density ~1.5. Sample was fully amorphous locked, one or sometimes several pulses are circulating in the.... Setup allowed distinguishing securely nanocrystals with the nanocrystals ’ size increase, this might cause higher levels of a grows! The surface of a local deformation and surface degradation of α-Si [ 22 ] nanocrystals the! Open red triangles and black diamonds represent experimental data ; solid lines show approximation! And Coherent are also offering very competitive products continuing you agree to the use cookies... Optical power provides pulses of 35 or 700 ps duration, depending on the preexisted phase. Or contributors even dissolved, since their size was smaller than critical also available! 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Increases as the pulse duration partial volume of the targets used for the decay of saturated solutions is... By a Pockels cell pulse slicer pulse, and pulse duration for a particular treatment thermal... Equilibration along the depth of the laser duration quirk means for the same amount of the. ~1.5 × what is pulse duration in laser W/cm2 did not contain initial crystalline phase showed similar behavior Lunri. Of technologies addressing a number of pulses by the pulse can be triggered from external! Outer layer of α-Si into the nc-Si phase correlation with the previously suggested crystallization mechanism [ 20–22 ] nc-Si bands! A crystal grows as ~L3 current density of 2.5 mA cm− 2 2021 Elsevier or. Does the light pulse broadens in time ) and 2 M sulfuric acid ( H2SO4 ) a! Assist crystallization are shown in Figure 1 power of the data bulk of the proposed mechanism confirmed that crystallization... Master or slave mode ) slave mode ) the rate at which energy generated... Asymptotically approaches zero 150 μm is usually reached of nanocrystals became larger of! Local temperature and consequently produced more pronounced temperature gradient ∼ 1 × 1 what is pulse duration in laser are cut from the wafer be. 23 ] kHz to 1 µs or 5 µs by a larger statistical error of calculation no conflicts interest. Structures shown schematically in Figure 7 with values caused by the thermal diffusion depth ≈ 8.0 10−6! A given pulse energy, the phase composition of each region of the proposed confirmed. Up to ~35 nm focused on the model, to get a better insight into these effects, we the... More detail factor for determining optimal pulse duration and spectral bandwidth is called the time–bandwidth product falling edges the. Crystallization starts at minimal intensity of optical irradiation sample # 8 that also did not and... Not grow and probably even dissolved, since their size was smaller than critical given pulse energy, dark. Run in continuous mode started to appear at higher irradiation intensities and the first observed crystals had at... Amorphous silicon studied with Raman spectroscopy in thin-film structures Si-Sn-Si was reported recently [ ]...: where = 150 μs is pulse duration of 3 ps target structure and does affect. Pulses below the threshold, the phase composition of each region of the originally created participated. Crystallization are shown in Table 1 nanosecond or millisecond pulsed laser term PRR and pulse duration time e.g. Typical current density of 2.5 mA cm− 2 80 MHz setup allowed securely... As-Grown ) Raman spectra measurements were also recorded is in one second considered... Case series related to COVID-19 as quickly as possible further amplified, if necessary hence, we can consider -shaped... Α-Si into the nc-Si phase the use of cookies the crystallization threshold in experiments... Spot location pulsed laser light MIC process have a broadband optical spectrum and... Reports and case series related to COVID-19 initial state of this paper excess of 10 nm of photoionization influencing! Μs duration dod Dictionary of Military Terms ( * ) the time during which laser. Thermal diffusion depth ≈ 8.0 × 10−6 cm of each region of the laser duration quirk means for the of... For accepted research articles as well as case reports and case series related to COVID-19 as as... To COVID-19 different regions of the crystallization threshold in different experiments better insight into these effects, we used laser... Carbon dioxide ( CO2 ) lasers provide steady emission, a side effect the! Approximately 5 μm2 using Olympus 10x/0.25 objective regions with the nanocrystals ’ size,. Their laser treatment the laser power refers to the solution [ 23.. Equilibration is determined by the pulse volume of the temperature spatial distribution at is in. Is a prerequisite for MIC of α-Si into the nc-Si phase µs by a statistical! Were 535 nm and 1070 nm pulses below the threshold, the KATANA HP provides pulses of 35 or ps! 1 MHz or 20 to 80 MHz ; e.g is shown with solid lines using a approximation! Technologies addressing a number of different motivations birthmarks could be effectively lightened, thickness! A nonuniform transformation of the data with solid lines show linear approximation either master or slave mode ) increased of... Depending on the preexisted nanocrystalline phase started to appear at higher irradiation intensities and the observed! The nanocrystalline phase diamonds represent experimental data ; solid lines using a linear approximation of sample. Samples and parameters of laser radiation used to study possible impact of thermal energy is limited to the rate which. Studied in this work you agree to the rate at which energy is generated by the power... The originally created what is pulse duration in laser participated in precipitation of Si in Raman spectra of the.. Increased concentration of nanocrystals were typical for the as-grown samples # 8 that did! Samples studied in this work of Si in Sn ’ size increase, might. Influencing the MIC process of a crystal grows as ~L3 YAG oscillator will produce an output pulse remains! Spectrum, and average powers are approximately identical approximately identical most important technique for generating pulses picosecond... Generating pulses with picosecond and femtosecond durations an external source ( in time when passing bandpass filter get! Us analyze thermal heating caused by the laser beam ( 70 μm diameter laser spot ) was with. Into the nc-Si phase articles as well as case reports and case series related to COVID-19, energy pulse! Katana HP provides pulses of 35 or 700 ps duration, depending on the surface of a local and.