We report the analysis of femtosecond laser modification of poly(methyl methacrylate) (PMMA) by detection of optical signals emitted from the sample coaxially with laser beam. The influence of pulse duration, energy and burst pattern on recorded spectra was investigated using TruMicro 2000 laser. We present images of internal structures in polymer as well as the spectra of conical emission created as result of laser – polymer interaction. Generation of a broadband continuum signal was detected and analysed in a function of position of the focal plane. Furthermore, third harmonic generation and second harmonic of fundamental 1030 nm wavelength was detected and the origin of these signals is discussed. We present possibility of the material modification process monitoring by in situ spectral analysis of light coming out from the sample. The deposited pulse energy fraction was analysed.
This paper presents results of poly(L-lactide) and poly(L-lactide)/hydroxyapatite composite cutting optimization using 2nd harmonic of femtosecond fiber laser. There are several limitations regarding the use of femtosecond lasers for processing of heat-sensitive medical grade polymers such as poly(L-lactide) (PLLA). Improper use of ultrashort pulse laser may lead to heat load into surrounding material causing its melting and crack formation when excessive energy is deposited and pulse repetition frequency is too high. The optimization of laser parameters is necessary not only because of heat but also due to reflection and scattering of incident light in high aspect ratio V-shaped groove resulting in decrease of ablation rate with an increasing number of repetitions. This problem is especially important in case of polymer foils thicker than 200 μm and the beam spot size which is typically around 15 - 30 μm in commercial systems. In this work we present threshold fluence and ablation rates for three types of material: amorphous PLLA, crystalline PLLA and PLLA/hydroxyapatite composite. For those materials in form of thick foils (∼400 μm) we performed cutting optimization. A significant improvement of cutting efficiency in case of thick foils was made by applying a method of multiple, overlapped cuts.
In this paper, for the first time, we present an analysis of changes of physicochemical properties of poly(L-lactide) induced by the femtosecond laser. Introduced changes were characterized using Differential Scanning Calorimetry, Gel Permeation Chromatography, X-ray Photoelectron Spectroscopy and Fourier Transform Infrared spectroscopy. We have noted that even for these process parameters for which no thermal ablation effects occurred, we observed some changes in material properties. In GPC image we recorded an increase in polydispersity index and some reduction of the molecular weight. The FTIR spectra show a reduction in the number of both C=O and C−O−C bonds in the polymer as well as the appearance of new bands. By using the XPS it was determined that processing with femtosecond laser cause a small oxidation of the surface layer. Decay of the spectra indicates the possibility of carboxyl (−COOH) and hydroxyl (−OH) groups present in the modified polymer. Although the observed changes are relatively small compared to long pulse duration lasers or UV lasers, they cannot be neglected in biopolymer applications for tissue engineering.
Laser-induced periodic surface structures (LIPSS) can appear in different forms such as ripples, grooves or cones. Those highly periodic wavy surface features which are frequently smaller than incident light wavelength bring possibility of nanostructuring of many different materials. Furthermore, by changing laser parameters one can obtain wide spectrum of periodicities and geometries. The aim of this research was to determine possibility of nanostructuring pyrolytic carbon (PyC) heart valve leaflets using different irradiation conditions. The study was performed using two laser sources with different pulse duration (15 ps, 450 fs) as well as different wavelengths (1064, 532, 355 nm). Both low and high spatial frequency LIPSS were observed for each set of irradiation parameters. In case femtosecond laser pulses we obtained deep subwavelength ripple period which was even ten times smaller than applied wavelength. Obtained ripple period was ranging from 90 up to 860 nm. Raman spectra revealed the increase of disorder after laser irradiation which was comparable for both pico- and femtosecond laser.
The main advantage of laser processing is a non-contact character of material removal and high precision attainable thanks to low laser beam dimensions. This technique enables forming a complex, submillimeter geometrical shapes such as vascular stents which cannot be manufactured using traditional techniques e.g. injection moulding or mechanical treatment. In the domain of nanosecond laser sources, an ArF excimer laser appears as a good candidate for laser micromachining of bioresorbable polymers such as poly(L-lactide). Due to long pulse duration, however, there is a risk of heat diffusion and accumulation in the material. In addition, due to short wavelength (193 nm) photochemical process can modify the chemical composition of ablated surfaces. The motivation for this research was to evaluate the influence of laser micromachining on physicochemical properties of poly(L-lactide). We performed calorimetric analysis of laser machined samples by using differential scanning calorimetry (DSC). It allowed us to find the optimal process parameters for heat affected zone (HAZ) reduction. The chemical composition of the ablated surface was investigated by FTIR in attenuated total reflectance (ATR) mode.
This paper presents a method that enables fast and low-cost fabrication of microchannels with oval cross-section. The procedure is based on formation of a concave meniscus at the interface between an initially cured PDMS and a polymeric mould fabricated using excimer laser. The replica is formed by expanding gas trapped within the structures of the mould during thermal curing. A second shaping factor is connected with surface phenomena at the interface between the mould, gas and partially cured PDMS. The final shape of the meniscus is determined when the PDMS reaches the high cure extent.
Laser micromachining systems based on excimer lasers are usually oriented to work with mask projection regime because of the low pulse repetition rate as well as large beam aperture of the laser source. In case of fabricating of the complex 3D structures, this approach introduces a number of limitations. Alternative solution might be usage of direct writing laser mode. Some examples of the so called contour ablation approach for fabricating microlenses with an absolutely monotonically changing cross-sectional profile are presented in the literature. Based on this idea and introducing new variables like automatic mask selection as well as optimizing process algorithms led us to obtain more versatile method for shape approximation. Hence, there were fabricated structures with cross-sectional profiles described as functions that are monotonic on specified intervals such as Fresnel microlenses. In this paper we describe approximation of process parameters for obtaining desired cross-sectional profiles and finally fabrication of few exemplary microlenses. All structures were characterized by a digital optical microscopy and compared to the given profiles. The accuracy of reproduction of the desired structures at the level of single microns was achieved.
In this paper an alternative method of manufacturing SRR structures through the selective removal of a thin layer of silver-palladium deposited on the surface of the Al2O3 ceramic by laser ablation process using nanosecond Nd:YAG laser (1064 nm) was presented. The SRR structures array were subject to transmittance measurements using the TDS (Time Domain Spectroscopy). Both electric and magnetic resonances were observed at frequencies determined by the structural parameters of the SRR. In case of the E field perpendicular to an SRR structure and one resonance area for 0.56 THz with the E field parallel to the structure, two characteristic resonant dips for 0.31 THz and 0.62 THz were obtained. Studies have confirmed that using selective laser removal process enables the preparation of the resonant structure in the range of THz.
In this paper, we present some examples of micromachining of poly(L-lactide) with a CO2 laser and an analysis of changes in material properties in the heat affected HAZ induced by the fluence well above the ablation threshold. The complexity of the processes of decomposition implies the need for simultaneous use of many selective analytical techniques which complement each other to give a full image of the changes. Introduced changes were characterized using Differential Scanning Calorimetry (DSC), Gel Permeation Chromatography (GPC), X-ray Photoelectron Spectroscopy (XPS) and Attenuated Total Reflectance Fourier Transform Infrared spectroscopy (ATR-FTIR). It turns out that CO2 laser processing of poly(L-lactide) mainly induces surface changes. However, oxidation of the surface was not observed. We recorded a bimodal distribution and some reduction in the molecular weight. Infrared spectroscopy in turn revealed the existence of absorption bands, characteristic for the vinyl groups (RCH=CH2). The appearance of these bands indicates that the decomposition of the polymer occurred, among others, by means of the cis-elimination reaction.
Laser-induced breakdown spectroscopy (LIBS) is a fast, fully optical method, that needs little or no sample preparation. In this technique qualitative and quantitative analysis is based on comparison. The determination of composition is generally based on the construction of a calibration curve namely the LIBS signal versus the concentration of the analyte. Typically, to calibrate the system, certified reference materials with known elemental composition are used. Nevertheless, such samples due to differences in the overall composition with respect to the used complex inorganic materials can influence significantly on the accuracy. There are also some intermediate factors which can cause imprecision in measurements, such as optical absorption, surface structure, thermal conductivity etc. This paper presents the calibration procedure performed with especially prepared pellets from the tested materials, which composition was previously defined. We also proposed methods of post-processing which allowed for mitigation of the matrix effects and for a reliable and accurate analysis. This technique was implemented for determination of trace elements in industrial copper concentrates standardized by conventional atomic absorption spectroscopy with a flame atomizer. A series of copper flotation concentrate samples was analyzed for contents of three elements, that is silver, cobalt and vanadium. It has been shown that the described technique can be used to qualitative and quantitative analyses of complex inorganic materials, such as copper flotation concentrates.
The irradiation of polylactide by KrF excimer laser with subthreshold fluence results in modification of its properties via photochemical reactions. A common approach is to modify chemical composition of polymer surface by UV irradiation, for example, in order to improve their wetting properties. In this paper, authors present a possibility of bulk modification of poly(L-lactide) which is related to photofragmentation and creation of new terminal groups. The irradiation results in decrease of molecular weight and increase of polydispersity. The appearance of new terminal groups is responsible for enhancement of absorption in UV-C range. The intensity of chemical composition changes introduced by UV irradiation can be precisely dosed thanks to a pulse character of laser source. Modifications can be controlled during the process by the analysis of energy transmitted through a polymer sheet. The distribution of absorption coefficient changes along with the depth of irradiated polymer and its correlation with polydispersity was discussed. Presented technique can be used for selective and controllable modification of hydrolytic degradation time of biodegradable polyesters utilized in biomedical applications.
In this paper a method for producing resonant structures using laser micromachining is presented. In the spot of laser
beam impact on AlN ceramics surface a conductive aluminum layer is formed. Compilation of process parameters allows
for the fabrication of structures with resistance at Rs ~ 0.01Ω/Rs. It has been also found out that the maximum value of resistance for which spiral resonator structures manifest their unique properties is at the level of Rs = 1.43 Ω.
Furthermore, the occurrence of mutual capacity which value is dependent on the arrangement of individual SR structures
with respect to each other was observed and examined. Based on satisfactory results for SR structures, it has been
attempted to produce a resonant structures dedicated to the THz range based on the process of direct metallization of
AlN ceramics surface. As a result, the Split Ring Resonator structure whose properties were verified by using the
THz -TDS method was manufactured. In case of the field E perpendicular to SRR structure and one resonance area for
0.50 THz with field E parallel to the structure, two characteristic resonant dips for 0.22 THz and 0.46 THz were
obtained. The studies confirmed that the method of direct metallization of AlN ceramics allows to produce resonant
structures in the THz range.
Aluminum nitride (AlN) ceramics has a unique characteristic, namely the ability to form conductive structures on its
surface directly by laser-induced decomposition of the base material. Various research has been carried out on obtaining
low-ohmic structures depending on process parameters such as the laser power, overlap of subsequent pulses and the
type of shielding gas (air, nitrogen and argon). This paper focuses on explaining which factors have the greatest impact
on the resistance (resistivity) value of obtained structures. In order to explain the effect of the laser fluence (below and
above the ablation threshold of aluminum nitride) on the chemical structure of the conductive layers, qualitative EDX
analyses were performed. Optimization of the process allowed obtaining a resistivity of the conductive layers at a level
of ρ = 0.64·10-6 Ω·m, with a thickness of aluminum up to 10 μm (sheet resistance RS = 10 mΩ/Sr). This technology can be
useful in making printed circuit boards (PCB), various types of sensors as well as radio-frequency identification (RFID)
and Lab-On-a-Chip (LOC) structures. This technology can also be useful for the production of metamaterials.
In this research the influence of laser micromachining on physicochemical properties of bioabsorbable polymer was
investigated. Poly(l-lactide) (PLLA), commonly used for manufacturing non-permanent biomedical devices, was
irradiated with varying fluences by CO2 laser and by KrF excimer laser. To evaluate modification of the material, several
analytical techniques were used: ATR (attenuated total reflection), XPS (X-ray photoelectron spectroscopy) and DSC
(differential scanning calorimetry). We found that the laser-affected material has lower glass transition (Tg) and melting
(Tm) temperatures. CO2 and KrF excimer lasers can be successfully used for cutting and drilling of polylactide.
KEYWORDS: Signal processing, Heterodyning, Digital signal processing, Semiconductor lasers, Signal detection, Laser applications, Fiber lasers, Electronics, Light scattering, Photodetectors
For the last few years we were elaborating the laser-fiber vibrometer working at 1550 nm. Our main stress was directed towards different aspects of research: analysis of scattered light, efficient photodetection, optimization of the fiber-free space interfaces and signal processing. As a consequence we proposed the idea of a multichannel fiber vibrometer based on well developed telecommunication technique – Wavelength Division Multiplexing (WDM). One of the most important parts of a fiber-laser vibrometer is demodulation electronic section. The distortion, nonlinearity, offset and added noise of measured signal come from electronic circuits and they have direct influence on finale measuring results. We present the results of finished project “Developing novel laser-fiber monitoring technologies to prevent environmental hazards from vibrating objects” where we have constructed a 4-channel WDM laser-fiber vibrometer.
This paper presents the analysis of the impact of selected process parameters on the resulting laser color marking. The
study was conducted for AISI 304 multipurpose stainless steel using a commercially available industrial fiber laser. It
was determined how various process parameters, such as laser power, scanning speed of the laser beam, temperature of
the material, location of the sample relative to the focal plane, affect the repeatability of the colors obtained. For
objective assessment of color changes, an optical spectrometer and the CIE color difference parameter ΔEab
* were used.
This paper presents another technique of manufacturing the unit cells of spiral-shaped resonators - SR on the aluminium nitride (AlN) ceramics. In this technique the AlN plane surface is irradiated by the Nd:YAG (1.06 μm). As a result of the supplied energy, the rupture of aluminium and nitrogen bonds occurs. Consequently, on the dielectric surface the conductive aluminium "paths" are formed. Obtaining the low-ohm conductive structures allows deploying this method to manufacture SR structures which can be used in antennas in order to reduce their coupling. An advantage of the demonstrated method is a possibility of selective and direct metallization of the AlN ceramics surface without a mask as it is required in photolithography process, which greatly reduces the implementation time of the projected metamaterials structures.
In this paper we present a device - fiber based coherent light source operating at 1550 nm wavelength and 5 W of the
output power. It is made completely of the fiber elements without any bulk optics therefore it is stable and resistant to the
environmental conditions. The main idea was to use so called MOPA (Master Oscillator Power Amplifier) configuration
to obtain universal design. Thus the device can be easily configured to work in couple different operation regimes.
KEYWORDS: Optical amplifiers, Semiconductor lasers, High power fiber amplifiers, High power lasers, Fiber amplifiers, Oscillators, Amplifiers, Fiber lasers, Laser applications, Cooling systems
In this work we present a high-power laser source developed in Master Oscillator Power Amplifier (MOPA)
configuration. Presented MOPA source consists of three amplifying stages: pre-amplifier based on erbium-doped fiber,
medium-power stage based on double-clad Er/Yb co-doped fiber and the power stage, based on Er/Yb co-doped doubleclad
LMA fiber. Whole system is set up in All-In-Fiber technique, without any bulk, free-space optical elements. It
provides over 20W of output power in the eye-safe 1550 nm band.
In this work we present a new design of Er/Yb co-doped fiber amplifier with controlled amplified spontaneous emission
(ASE) at 1 μm. The Yb-ASE is controlled by stimulating a laser emission at 1064 nm in the amplifier, by providing
a positive 1 μm signal feedback loop. The results were discussed and compared to a conventional amplifier setup without
1 μm ASE control. We have shown, that applying a 1064 nm signal loop in an Er/Yb amplifier can increase the output
power at 1550 nm and provide stable operation without parasitic lasing at 1 μm.
In this paper the development and optimization process of single frequency, diode pumped Nd:YVO4/YVO4/KTP
microchip laser operating at 532nm is presented. A birefringent filter formed by beam displacer (undoped YVO4 crystal)
and KTP crystal was used to obtain single mode operation. As a final result of optimization miniature, monolithic laser
resonator was elaborated. The laser generated Gaussian beam with quality better than M2<1.2 and maximum single
frequency output power at the level of 160mW @ 532 nm. The optical to optical efficiency (532nm to 808nm) was at the
level of 16,8% at the maximum single frequency output power.
We have developed a laser vibrometer based on a Nd:YVO4/YVO4/KTP monolithic single-frequency green laser
operating at 532 nm with narrow linewidth of radiation (~85kHz). Two configurations of laser Doppler vibrometer have
been investigate - with so-called single- and double-frequency Bragg shifts. Measurement of heterodyne signals as a
mixing result of scattered and reference beams has been performed. In both configurations we have obtained signals with
high S/N ratio >30 dB with Resolution Bandwidth RBW = 200 kHz for a vibrometer output power of 3 mW. In our
opinion, stable single-frequency solid-state green lasers provide new opportunities for the development of miniature laser
vibrometry.
The WDM fiber transmission technique was used to measure vibration parameters of four points of a vibrating object.
The 4-independent laser diodes form a WDM system according to the rule 'one wavelength-one analyzed point'.
Keywords: laser Doppler vibrometry, fibre vibrometry, heterodyne detection, multichannel vibrometry.
In this paper the practical realization of a single frequency, monolithic diode pumped Nd:YVO4/YVO4/KTP microchip
laser operating at 532nm is presented. The optical crystals formed the laser resonator were bonded together with UV
curable adhesive. Elementary analysis of the single mode operation of such a laser configuration is presented. Period of
the Lyot filter, temperature mode-hop free range of designed laser was calculated. The single frequency operation has
been obtained in a birefringent filter, where an YVO4 beam displacer acts as an ideal polarizer. We have obtained stable
single frequency operation, in the two spectral ranges around 1064nm. Investigation of the single frequency operation
range shifting with pump power was done. Experimental results are in good agreement with theoretical analysis. The
laser operated with output power up to 85mW at 532nm. The total optical efficiency (808nm to 532nm) was 9%. The
beam has a Gaussian profile and the M2 parameter was at the level of 1.2.
We have developed the photonic sensor of electromagnetic field. The electrooptical phase modulator inserted in one laser cavity performs frequency modulation of the laser due to voltage induced in the antenna probe. The heterodyne detection allows to move the spectrum of modulated optical frequencies into the RF or microwave ranges. The issue of our solution is inserting of both lasers (signal and reference) in the common construction in order to minimize fluctuation of offset frequency. The pumping of the microchip lasers and transmission of the signal are guided via optical fibers. The setup can be all dielectric (apart of antenna). The sensitivity of laser tuning with an electrooptical modulator i.e. the value of frequency deviation due to driven voltage is linearly proportional to the free spectral range of the laser and inversely proportional to the "half-wavelength" voltage of an used modulator. In our case this sensitivity is about 10 MHz/V, with the free spectral range νq congruent to 28 GHz. The sensitivity is quite high, even when the offset frequency fluctuation, caused mainly by thermal drift, are taken in account. Apart from the heterodyne technique of optical FM detection we have introduce here detection with the external Fabry-Perot cavity
KEYWORDS: Electro optics, Modulators, Laser stabilization, Electrooptic modulators, Radio optics, Laser applications, Telecommunications, Frequency division multiplexing, Laser systems engineering, Control systems
The idea of coherent optical communications with frequency division multiplexing gives larger possibilities and new qualities compare to IM-DD (Intensity Modulation - Direct Detection) systems. However, optical coherent systems are much more complicated in realization then their "radio" counterparts. These optical FM systems require stable and controllable offset lasers. Heterodynes of microchip lasers with offset frequency stabilization are presented.
The control systems of laser frequency stabilization use a few mechanisms of tuning: thermal, piezoelectric and electro optic. Thermal tuning is a very slow process but it enables to tune the resonator laser even over few tens of microns. Piezoelectric tuning is usually limited to a few of microns and in the frequency band of tens of Hz. The electro optic phase modulator inserted inside a laser resonator gives the fastest tuning in the band of few tens of kHz.
The paper describes investigations of vibrations by the laser interferometry where both beams are offset in frequency. This method is called the laser heterodyne vibrometry. The main aim of this investigation was heterodyne detection of a weak laser light scattered from a vibrating object. As a standard surface we used a piece of white zero sheet connected to the vibrating object.
Any dynamic small changes of refractive index of a measurand, which are on the level of 10-6 and less can be detected by inserting a measured object inside a stable laser cavity. Using heterodyne detection technique these changes can be measured with high resolution.
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