Influence Of Laser Wavelength Research Articles

Observation of Plasma Behavior in Micro-machining of Ceramics by Harmonics of Nd:YAG Laser

Precision micro-machining without cracks and with a narrow heat affected zone is highly required for the effective use of high-performance material. For this purpose, it is expected that the higher harmonics of Nd:YAG laser could perform the precision micro-machining by its high photon energy. However, even using harmonics of Nd:YAG laser, the heat affected zone is inevitable due to the plasma generation. In order to reduce the influence of plasma, it is important to understand the generation mechanism of plasma. Therefore, the laser induced plasma was observed by the high-speed shutter camera, and the influence of laser wavelength on machining characteristics was investigated.

Influence of laser wavelength and beam profile on Nd 3+:YAG laser assisted formation of polycrystalline-Si films

Influence of wavelengths and beam profiles of a pulsed Nd 3+:YAG laser on the formation of a polycrystalline-silicon (poly-Si) on a-Si thin film is investigated. Two sets of samples of amorphous-Silicon (a-Si) thin films deposited on glass (a-Si/glass) and crystalline Si (a-Si/c-Si) substrates were treated with different laser-fluence values. After the laser treatment, the films were analyzed by a scanning electron microscope, the Raman spectroscopy technique and the resistance-measurement technique. In the case of the third harmonics (355 nm) of the Nd 3+:YAG laser, poly-Si films were obtained with laser-fluence values ranging from 260 mJ/cm 2 to 560 mJ/cm 2, where as in the case of the second harmonics (532 nm), the process window for the formation of poly-Si films, in terms of the laser fluence, was ranging from 300 mJ/cm 2 to 480 mJ/cm 2. On the other hand, in the case of samples treated with the fundamental wavelength (1064 nm), a narrow process window with higher laser-fluence values around 1100 mJ/cm 2 was observed. Further, the substrate was also affected because of the higher laser-fluence value. It has also been observed that the crystallization characteristics of poly-Si films improved with the flat-top intensity distribution as compared to the Gaussian intensity distribution of the Nd 3+:YAG laser beam. A theoretical simulation based on thermal modeling was performed to understand the mechanism of crystallization.

Dendrimer-Capped Nanoparticles Prepared by Picosecond Laser Ablation in Liquid Environment

Fifth generation ethylendiamine-core poly(amidoamine) (PAMAM G5) is presented as an efficient capping agent for the preparation of metal and semiconductor nanoparticles by ps laser ablation in water. In particular, we describe results obtained with the fundamental, second and third harmonic of a ps Nd:YAG laser and the influence of laser wavelength and pulse energy on gold particle production and subsequent photofragmentation. In this framework, the role of the dendrimer and, in particular, its interactions with gold clusters and cations are accounted.

Influence of wavelength, irradiance, and the buffer gas pressure on high irradiance laser ablation and ionization source coupled with an orthogonal Time of Flight Mass Spectrometer

Influence of laser wavelength, laser irradiance and the buffer gas pressure were studied in high irradiance laser ablation and ionization source coupled with an orthogonal time-of-flight mass spectrometer. Collisional cooling effects of energetic plasma ions were proved to vary significantly with the elemental mass number. Effective dissociation of interferential polyatomic ions in the ion source, resulting from collision and from high laser irradiance, was verified. Investigation of relative sensitivity coefficients (RSC) of different elements performed on a steel standard GBW01396, which was ablated at 1064 nm, 532 nm, 355 nm, and 266 nm, has demonstrated that the thermal ablation mechanism could play a critical role with the first three wavelengths, while 266 nm induces non-thermal ablation principally. Experimental results also indicated that there is no evident discrepancy for most metal elements on RSCs and LODs among four wavelengths at high irradiance, except that high boiling point elements like Nb, Mo, and W have higher RSCs at higher irradiance regions of 1064 nm, 532 nm, and 355 nm due to thermal ablation. A geological standard and a garnet stone were also used in the experiment subsequently, and their RSCs and LODs for metal elements show nonsignificant dependence on wavelength at designated irradiances. All results reveal that relatively uniform sensitivity can be achieved at any wavelength for metal elements in the solids used in our experiments at an appropriate irradiance for the low pressure high irradiance laser ablation and ionization source.

Comparison of 1064 nm and 266 nm excitation of laser-induced plasmas for several types of plastics and one explosive

Comparative measurements of Laser-Induced Breakdown Spectroscopy (LIBS) for ultraviolet (UV) and near infrared (NIR) excitation wavelengths on a wide range of plastics and one kind of explosive are presented. The focus of work is on the influence of laser wavelength on the Signal-to-peak to peak noise ratio (SPPNR) for selected emission lines as well as the plasma thresholds for NIR and UV excitation wavelengths. The merits of both excitation wavelengths are discussed with respect to the detection of explosives.

The use of combination of nonlinear optical materials to control terahertz pulse generation and detection

We suggest composite nonlinear optical media based on the pair of ZnTe and GaP crystals for terahertz pulse detection or generation. The influence of laser wavelength, pulse duration, and media thickness on the terahertz pulse conversion are studied. The optimization of the composite structure performed numerically allowed for essential improvement of the phase-matching condition observed in the experiment.

Influence of laser wavelength and pulse duration on the degradation of polymeric films embedding photochromic molecules

An extensive investigation of the photodegradation of the photochromic molecule 1′,3′-dihydro-1′,3′,3′-trimethyl-6-nitrospiro[2 H-1-benzopyran-2,2′-(2 H)-indole] in a polymer matrix is studied under irradiation with ultraviolet (UV) laser pulses of 248 and 308 nm wavelength. Apart from the effect of the wavelength, the effect of the pulse duration is also presented using pulses of 30 ns and 500 fs for the 248 nm wavelength. To tackle the problem of oxidative degradation upon irradiation of the photochromic molecules which is known to play a principal role in the photodegradation process, we incorporate Iron(II) phthalocyanine molecules in the examined matrices. These molecules upon UV irradiation are dissociated into photoproducts that can interact efficiently with electron acceptor groups in the polymer, partly responsible for the photochromic degradation. The phthalocyanine molecules seem to protect efficiently the photochromic molecules only at low laser fluences. Moreover, in the case of ultrashort pulses the degradation of the photochromic molecules is found to be more intense that in the case of ns pulses, indicating multiphoton absorption mechanisms, unless low laser fluences are used.

Pulsed Laser Deposition of Hafnium Oxide on Silicon

Hafnium oxide films were prepared by Pulsed Laser Deposition (PLD). The influence of laser wavelength (fundamental, second and third harmonic of a Nd:YAG laser), used for evaporation, and substrate temperature on the film morphology, chemical structure and interfacial quality were investigated yielding the following results: While the laser wavelength exhibits minor influence on layer structure, the substrate temperature plays a critical role regarding morphological and chemical structure of the produced hafnium oxide / silicon stacks. Atomic Force Microscopy (AFM) images show a clear transition from smooth layers consisting of small area crystallites to very rough surfaces characterized by large craters and regular, plane features when the growth temperature was increased. These facts suggest a chemical instability which is confirmed by X-ray Photoelectron Spectroscopy (XPS). Investigations of the hafnium and silicon core level spectra indicate the occurrence of silicon dioxide and hafnium silicide in the case the samples were produced at elevated temperatures.

Influence of laser wavelength and pulse duration on gas bubble formation in blood filled glass capillaries

Hypervascular skin lesions (HVSL) are treated with medical lasers characterized by a variety of parameters such as wavelength lambda, pulse duration t(p), and radiant exposure E that can be adjusted for different pathology and blood vessel size. Treatment parameters have been optimized assuming constant optical properties of blood during laser photocoagulation. However, recent studies suggest that this assumption may not always be true. Our objective was to quantify thermally induced changes in blood that occur during irradiation using standard laser parameters. Glass capillary tubes (diameter D = 100, 200, and 337 microm) filled with fresh or hemolyzed rabbit blood were irradiated once at lambda = 585, 595, or 600 nm, t(p) = 1.5 milliseconds; and also at lambda = 585 nm, t(p) = 0.45 milliseconds. E was increased until blood ablation caused formation of permanent gas bubbles. In a corroborative study, human blood was heated at 50 degrees C and absorbance spectra were measured as a function of time. Threshold radiant exposure, E(thresh), for gas bubble formation was found not to depend on lambda, which might be surprising in view of the 10-fold lower absorption coefficient at 600 nm as compared to 585 nm. The spectroscopic study revealed heat-induced changes in blood constituent composition of hemoglobins (Hb) from initially 100% oxyhemoglobin (HbO2) to deoxyhemoglobin (HHb) and, ultimately, methemoglobin (metHb) as the major constituent. Model calculations of E(thresh)(lambda,D) based on changing constituent blood composition during heating with milliseconds lasers were found to correlate with experimental results. For laser treatment of HVSL it appears that lambda is of secondary importance and that the choice of t(p) is a more important factor.

Structural influence on charge-carrier lifetimes in TiO2 powders studied by microwave absorption

A set-up for contactless transient photoconductivity measurements on powders by the Time Resolved Microwave Photoconductivity (TRMC) method has been realized. These measurements have been used as a tool for the investigation of excess charge-carrier lifetimes in TiO2 (anatase and rutile) powders. The influence of laser wavelength and intensity on TRMC decay shows the importance of the fast-recombination processes. The presence of a long time tail in the TRMC signals of the anatase modification of TiO2 is attributed to quenching of this recombination by hole-trapping at the surface. The influence of surface treatment by ethanol and water on TRMC decay evidences that dominant effects are bulk recombination in rutile and surface trapping in anatase. The influence of doping in rutile shows that increasing the doping rate accelerates the decay whatever the doping type is. The doping element acts as an impurity favoring recombination by creation of structural defects. The influence of thermal treatment in anatase shows that increasing the thermal treatment temperature increases the lifetimes. High crystalline quality leads to long charge-carrier lifetimes. The results are discussed in view of their relevance for photocatalysis.

Preparation of metal colloids by a laser ablation technique in solution: influence of laser wavelength on the ablation efficiency (II)

Laser ablations of silver and copper targets in water were performed to prepare nanosize metal colloids. The influence of the laser wavelength, focusing conditions, and laser fluence on the ablation efficiency was studied. The relation between the ablation efficiency and wavelength varied with laser fluence. The ablation efficiency at shorter wavelengths was higher at low fluence, while the ablation efficiency at longer wavelengths was higher at high fluence. These findings were discussed in terms of the “intra-pulse” and “inter-pulse” self-absorptions of the incident laser light by colloidal particles.

Laser ablation of Upilex-S polyimide: influence of laser wavelength on chemical structure and composition in both ablated area and halo

Blind craters (diameter 200 μm) on Upilex-S polyimide films (80-μm thick) were drilled by irradiation with three different laser systems [KrF excimer: wavelength λ=248 nm (UV); acoustic optical Q-switch Nd:YAG: λ=355 nm (UV); and TEA CO 2: λ≈9.3 μm (IR)] in air. Modifications of chemical structure and surface morphology in both the ablated area and halo were examined using X-ray photoelectron spectroscopy (XPS) and a scanning electron microscope (SEM). In the halo, nano-particles were observed with UV lasers, but submicro-particles were observed with the IR laser. The results of XPS analysis show that the C content increased, while the O content and N content decreased in the ablated area at all wavelengths, due to photo-thermal or photochemical decomposition of polyimide. These are substantiated by decreases of the carbonyl groups (CO) at 288.2 eV and an increase of CC groups at 284.8 eV. However, the N content in the ablated area with TEA CO 2 laser is higher than that with UV lasers. Also, amide groups were detected in the ablated area with TEA CO 2 laser and 355-nm Nd:YAG laser, but few with 248-nm excimer laser. Furthermore, in the halo, the O content with the 355-nm laser is higher than that of the 248-nm laser. Also, the shoulder of C 1s peak was observed at 288.5 eV in the halo due to oxidation of fragments erupted from the plume in air, but did not occur at the 248-nm wavelength. These findings indicate that the chemical structure and composition are highly dependent on laser wavelength.

Influence of Irradiation Wavelength on Atomic Emission Spectroscopy Using Laser Ablation

In this study, the influence of laser wavelengths on atomic emission spectroscopy using laser ablation for samples (glass, polymer, Si, and Cu) has been investigated using 1064 nm and 266 nm pulses of a Q-switched Nd:YAG laser. The threshold fluence is decreased and the emission intensity is increased for UV laser ablation, compared with IR laser ablation. Simultaneous irradiation by both IR and UV pulses has also been found in decreasing the threshold and increasing the emission intensity.

Influence of laser wavelength on activation of ZrO2 ceramics for electroless metal plating

Influence of laser wavelength on activation of ZrO2 ceramics for electroless metal plating

Experimental determination of thermal and nonthermal mechanisms for laser desorption from thin metal films

The mechanism of laser desorption of peptides as negative ions from Au thin films with 193, 248 and 351 nm laser radiation has been studied. Variation of the threshold laser power density with metal film thickness is used to distinguish between thermal and nonthermal mechanisms. The influence of laser wavelength on the desorption of peptides with different optical absorption spectra has been studied. Thermal desorption is observed when 351 nm laser radiation is utilized. However, both 248 and 193 nm radiation result in nonthermal desorption processes. At 248 nm, the threshold power density is observed to be independent of the optical absorption of the peptide adsorbate, supporting suggestions that a mechanism involving excitation of hot electrons in the metal is important.

The selective dissociation of SF6 in an intense ir field: A molecular beam study on the influence of laser wavelength and energy

We report the results of a molecular beam study on the energy fluence and wavelength dependence of the dissociation probability of SF6. We find surprisingly high values at power densities which rule out an essential contribution of power broadening but rather stress the importance of efficient absorption in the lower levels. No loss of isotopic selectivity is observed for power densities up to 108 W/cm2 in the P (20) line at 944.2 cm−1.