Ultrafast dynamic ellipsometry, a technique that probes a sample with chirped laser pulses at two angles and with two orthogonal polarizations, was used to measure the effective refractive index across the ablation region of a Si(111) wafer exposed to a 100 fs ablation pulse. The resulting refractive index data show a significant increase in the extinction coefficient, indicative of the melting of silicon.
{"title":"Ultrafast dynamic ellipsometry of laser ablated silicon","authors":"C. Bolme, S. McGrane, D. Moore, D. J. Funk","doi":"10.1117/12.782739","DOIUrl":"https://doi.org/10.1117/12.782739","url":null,"abstract":"Ultrafast dynamic ellipsometry, a technique that probes a sample with chirped laser pulses at two angles and with two orthogonal polarizations, was used to measure the effective refractive index across the ablation region of a Si(111) wafer exposed to a 100 fs ablation pulse. The resulting refractive index data show a significant increase in the extinction coefficient, indicative of the melting of silicon.","PeriodicalId":249315,"journal":{"name":"High-Power Laser Ablation","volume":"105 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2008-05-08","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"124174321","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
The aim of this paper is to give a critical review of the influence of constant effective-mass approximation on the results provided by current theoretical models of laser-induced ionization of the solids transparent at input laser wavelength. Making transparent qualitative analysis of the models, we come to conclusion that assuming electrons and holes to have constant effective mass, one eliminates specific photo-ionization effects taking place at high intensity. The assumption of constant effective mass of conduction-band electrons is also shown to provide wrong description of the avalanche ionization almost at any laser wavelength and intensity. The presented analysis allows to give simple quantitative criteria determining the range of laser and material parameters for which the effective mass can be assumed constant.
{"title":"Theoretical models of laser-induced ionization of transparent materials: current issues and recent improvements","authors":"V. Gruzdev","doi":"10.1117/12.784567","DOIUrl":"https://doi.org/10.1117/12.784567","url":null,"abstract":"The aim of this paper is to give a critical review of the influence of constant effective-mass approximation on the results provided by current theoretical models of laser-induced ionization of the solids transparent at input laser wavelength. Making transparent qualitative analysis of the models, we come to conclusion that assuming electrons and holes to have constant effective mass, one eliminates specific photo-ionization effects taking place at high intensity. The assumption of constant effective mass of conduction-band electrons is also shown to provide wrong description of the avalanche ionization almost at any laser wavelength and intensity. The presented analysis allows to give simple quantitative criteria determining the range of laser and material parameters for which the effective mass can be assumed constant.","PeriodicalId":249315,"journal":{"name":"High-Power Laser Ablation","volume":"363 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2008-05-08","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"134499671","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
The present study deals with calibration-free analysis of materials by Laser-Induced Breakdown Spectroscopy (LIBS). A numerical code computes the spectral radiance emitted from a plasma in local thermal equilibrium. The numerical code includes the calculation of the plasma composition by solving the system of Saha-equations, mass conservation and neutrality equation. The chemical reactions within the plasma plume are considered, especially in case of organic materials ablation. The line intensities are then computed. In the present study, the lines are considered to be optically thin. The modeling of the chemical composition of an organic material and a steel sample is presented. Comparing the experimental spectra to the computed ones, it was possible to measure the elemental concentrations of the steel with good accuracy without any requirement of preliminary calibration.
{"title":"Organic and inorganic materials analysis by laser-induced breakdown spectroscopy","authors":"F. Brygo, J. Hermann","doi":"10.1117/12.782706","DOIUrl":"https://doi.org/10.1117/12.782706","url":null,"abstract":"The present study deals with calibration-free analysis of materials by Laser-Induced Breakdown Spectroscopy (LIBS). A numerical code computes the spectral radiance emitted from a plasma in local thermal equilibrium. The numerical code includes the calculation of the plasma composition by solving the system of Saha-equations, mass conservation and neutrality equation. The chemical reactions within the plasma plume are considered, especially in case of organic materials ablation. The line intensities are then computed. In the present study, the lines are considered to be optically thin. The modeling of the chemical composition of an organic material and a steel sample is presented. Comparing the experimental spectra to the computed ones, it was possible to measure the elemental concentrations of the steel with good accuracy without any requirement of preliminary calibration.","PeriodicalId":249315,"journal":{"name":"High-Power Laser Ablation","volume":"3 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2008-05-08","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"132859884","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Diode pumped alkali lasers have developed rapidly since their first demonstration. These lasers offer a path to convert highly efficient, but relatively low brightness, laser diodes into a single high power, high brightness beam. General Atomics has been engaged in the development of DPALs with scalable architectures. We have examined different species and pump characteristics. We show that high absorption can be achieved even when the pump source bandwidth is several times the absorption bandwidth. In addition, we present experimental results for both potassium and rubidium systems pumped with a 0.2 nm bandwidth alexandrite laser. These data show slope efficiencies of 67% and 72% respectively.
{"title":"High power diode pumped alkali vapor lasers","authors":"J. Zweiback, B. Krupke","doi":"10.1117/12.782704","DOIUrl":"https://doi.org/10.1117/12.782704","url":null,"abstract":"Diode pumped alkali lasers have developed rapidly since their first demonstration. These lasers offer a path to convert highly efficient, but relatively low brightness, laser diodes into a single high power, high brightness beam. General Atomics has been engaged in the development of DPALs with scalable architectures. We have examined different species and pump characteristics. We show that high absorption can be achieved even when the pump source bandwidth is several times the absorption bandwidth. In addition, we present experimental results for both potassium and rubidium systems pumped with a 0.2 nm bandwidth alexandrite laser. These data show slope efficiencies of 67% and 72% respectively.","PeriodicalId":249315,"journal":{"name":"High-Power Laser Ablation","volume":"66 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2008-05-08","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"129217055","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
J. Bruzzese, M. Nishihara, A. Hicks, W. Lempert, J. Rich, I. Adamovich
The paper discusses optimization of gain and output power and scaling of a pulser-sustainer discharge excited oxygen-iodine laser. For this, NO addition to the laser mixture and iodine vapor dissociation in an auxiliary high-voltage, nanosecond pulse duration, repetitively pulsed discharge ("side" discharge) are used. Iodine dissociation fraction generated in the side discharge and measured in the M=3 laser cavity is up to 50%. The experiments showed that additional iodine dissociation generated in the side discharge only moderately increased laser gain, by 10-15%. Parametric gain optimization by varying main discharge pressure, O2 and NO fractions in the flow, I2 flow rate, pulsed discharge frequency, and sustainer discharge power, with the side discharge in operation produced gain up to 0.08 %/cm. Two parameters that critically affect gain are the energy loading per molecule in the discharge and the NO flow rate controlling the O atom concentration in the flow. Operation at the main discharge pressure of 60 torr resulted in significantly higher gain than at 100 torr, 0.080 %/cm vs. 0.043 %/cm, due to high discharge energy loading per molecule at the lower pressure. Laser output power measured at the gain optimized conditions is 1.4 W. Experiments with a scaled-up laser with a large volume pulser-sustainer discharge (10 cm x 10 cm x 2 cm vs. 5 cm x 5 cm x 2 cm) and longer gain path (10 cm vs. 5 cm) demonstrated stable discharge operation at discharge powers up to at least 2.9 kW. Singlet delta yield and gain measurements in the scaled-up laser are underway.
本文讨论了脉冲持续放电激发氧碘激光器的增益优化、输出功率优化和标度问题。为此，在激光混合物中加入一氧化氮并在辅助高压下解离碘蒸气，脉冲持续时间为纳秒，采用重复脉冲放电(“侧”放电)。侧放电产生的碘解离率在M=3激光腔内测量达到50%。实验表明，在侧放电中产生的额外碘解离只能适度地增加激光增益，约为10-15%。通过改变主放电压力、流动中O2和NO组分、I2流量、脉冲放电频率和持续放电功率对参数增益进行优化，其中运行侧放电的增益可达0.08% /cm。影响增益的两个关键参数是放电中每个分子的能量负荷和控制流中O原子浓度的NO流速。在主放电压力为60 torr时，由于在较低压力下每个分子的放电能量负载较高，其增益显著高于100 torr时的增益(0.080% /cm vs. 0.043% /cm)。在增益优化条件下测量到的激光输出功率为1.4 W。实验表明，在放电功率至少为2.9 kW的情况下，具有大体积脉冲保持放电(10 cm × 10 cm × 2 cm vs. 5 cm × 5 cm)和更长的增益路径(10 cm vs. 5 cm)的放大激光器具有稳定的放电操作。单重态δ产率和增益测量正在进行中。
{"title":"Optimization and scaling of a pulser-sustainer discharge excited oxygen-iodine laser","authors":"J. Bruzzese, M. Nishihara, A. Hicks, W. Lempert, J. Rich, I. Adamovich","doi":"10.1117/12.783781","DOIUrl":"https://doi.org/10.1117/12.783781","url":null,"abstract":"The paper discusses optimization of gain and output power and scaling of a pulser-sustainer discharge excited oxygen-iodine laser. For this, NO addition to the laser mixture and iodine vapor dissociation in an auxiliary high-voltage, nanosecond pulse duration, repetitively pulsed discharge (\"side\" discharge) are used. Iodine dissociation fraction generated in the side discharge and measured in the M=3 laser cavity is up to 50%. The experiments showed that additional iodine dissociation generated in the side discharge only moderately increased laser gain, by 10-15%. Parametric gain optimization by varying main discharge pressure, O2 and NO fractions in the flow, I2 flow rate, pulsed discharge frequency, and sustainer discharge power, with the side discharge in operation produced gain up to 0.08 %/cm. Two parameters that critically affect gain are the energy loading per molecule in the discharge and the NO flow rate controlling the O atom concentration in the flow. Operation at the main discharge pressure of 60 torr resulted in significantly higher gain than at 100 torr, 0.080 %/cm vs. 0.043 %/cm, due to high discharge energy loading per molecule at the lower pressure. Laser output power measured at the gain optimized conditions is 1.4 W. Experiments with a scaled-up laser with a large volume pulser-sustainer discharge (10 cm x 10 cm x 2 cm vs. 5 cm x 5 cm x 2 cm) and longer gain path (10 cm vs. 5 cm) demonstrated stable discharge operation at discharge powers up to at least 2.9 kW. Singlet delta yield and gain measurements in the scaled-up laser are underway.","PeriodicalId":249315,"journal":{"name":"High-Power Laser Ablation","volume":"929 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2008-05-08","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"123059429","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
F. N. Ljubchenko, A. V. Fedenev, A. Chumakov, N. Bosak, V. Tarasenko, A. N. Panchenko
Problems of laser-plasma thruster development for space applications are analyzed. Results of laboratory research concerning the choice of solid-state laser, operating mode and target material are considered. Characteristics of micro-thruster with diode pumping are discussed.
{"title":"Novel concept of laser-plasma microthruster design","authors":"F. N. Ljubchenko, A. V. Fedenev, A. Chumakov, N. Bosak, V. Tarasenko, A. N. Panchenko","doi":"10.1117/12.786659","DOIUrl":"https://doi.org/10.1117/12.786659","url":null,"abstract":"Problems of laser-plasma thruster development for space applications are analyzed. Results of laboratory research concerning the choice of solid-state laser, operating mode and target material are considered. Characteristics of micro-thruster with diode pumping are discussed.","PeriodicalId":249315,"journal":{"name":"High-Power Laser Ablation","volume":"2 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2008-05-08","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"122573110","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Photolithography is well established in the fabrication of microfluidic networks; however, it is difficult to fabricate designs which require multiple depths. Furthermore, the cost/time to produce photolithographic masks is problematic, particularly when prototyping. Here we describe fabrication of microfluidic branching networks with multi-depth structures, ranging from 10s to 100s of microns, using a femtosecond fiber laser with 10 W average power, followed by chemical etching in a 10:1 solution of 49% HF and 69% HNO3. While this technique was originally developed using a nanosecond laser, this unique femtosecond laser enables greater processing precision and faster overall processing speed.
{"title":"Fabrication of microfluidic networks using a high power femtosecond fiber laser","authors":"L. Shah, D. Kam, J. Mazumder","doi":"10.1117/12.782655","DOIUrl":"https://doi.org/10.1117/12.782655","url":null,"abstract":"Photolithography is well established in the fabrication of microfluidic networks; however, it is difficult to fabricate designs which require multiple depths. Furthermore, the cost/time to produce photolithographic masks is problematic, particularly when prototyping. Here we describe fabrication of microfluidic branching networks with multi-depth structures, ranging from 10s to 100s of microns, using a femtosecond fiber laser with 10 W average power, followed by chemical etching in a 10:1 solution of 49% HF and 69% HNO3. While this technique was originally developed using a nanosecond laser, this unique femtosecond laser enables greater processing precision and faster overall processing speed.","PeriodicalId":249315,"journal":{"name":"High-Power Laser Ablation","volume":"10 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2008-05-08","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"114142560","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
We model an interaction of femtosecond laser pulses (800 nm, 100 fs, 10E12-10E14 W/cm2) with metal targets (Al, Au, Cu and Ni). A detailed analysis of laser-induced phase transitions, melting wave propagation and material decomposition is performed using a thermodynamically complete two-temperature equation of state with stable and metastable phases. Material evaporation from the surface of the target and fast melting wave propagation into the bulk are observed. On rarefaction the liquid phase becomes metastable and its lifetime is estimated using the theory of homogeneous nucleation. Mechanical fragmentation of the target material at high strain rates is also possible as a result of void growth and confluence. In our simulation several ablation mechanisms are observed but the major output of the material is found to originate from the metastable liquid state. It can be decomposed either into a liquid-gas mixture in the vicinity of the critical point, or into droplets at high strain rates and negative pressure. The simulation results correlate with available experiments.
{"title":"Implementation of kinetics of phase transitions into hydrocode for simulation of laser ablation","authors":"M. Povarnitsyn, P. Levashov, K. Khishchenko","doi":"10.1117/12.782581","DOIUrl":"https://doi.org/10.1117/12.782581","url":null,"abstract":"We model an interaction of femtosecond laser pulses (800 nm, 100 fs, 10E12-10E14 W/cm2) with metal targets (Al, Au, Cu and Ni). A detailed analysis of laser-induced phase transitions, melting wave propagation and material decomposition is performed using a thermodynamically complete two-temperature equation of state with stable and metastable phases. Material evaporation from the surface of the target and fast melting wave propagation into the bulk are observed. On rarefaction the liquid phase becomes metastable and its lifetime is estimated using the theory of homogeneous nucleation. Mechanical fragmentation of the target material at high strain rates is also possible as a result of void growth and confluence. In our simulation several ablation mechanisms are observed but the major output of the material is found to originate from the metastable liquid state. It can be decomposed either into a liquid-gas mixture in the vicinity of the critical point, or into droplets at high strain rates and negative pressure. The simulation results correlate with available experiments.","PeriodicalId":249315,"journal":{"name":"High-Power Laser Ablation","volume":"1 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2008-05-08","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"123202788","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Ice made of ultrapure water or water doped with 1 % polymer (polyethylene glycol, "PEG") was irradiated by laser light with fluences between 2 and 80 J/cm2 in the ultraviolet (UV) regime at 355 nm and in the infrared (IR) regime at 1064 nm in vacuum. In the UV regime there is a threshold for plasma formation at 3.5 J/cm2, whereas the threshold is at 8.5 J/cm2 in the IR regime. The ions from the plasma plume were studied by a Langmuir probe. The ion yield was much higher for UV laser irradiation than for IR laser irradiation. The peak of the time-of-flight spectra comprises ions of velocity from 60 to 110 km/s. Generally, the ion yield was slightly larger for ice samples doped with PEG than for pure ones. The threshold behavior was much more pronounced in the IR regime than in the UV regime. These results indicate that the behavior of the plasma current can be understood in terms of ionization breakdown at the ice surface.
{"title":"Laser-induced plasma from pure and doped water-ice at high fluence by ultraviolet and infrared radiation","authors":"J. Schou, A. Matei, K. Rodrigo, M. Dinescu","doi":"10.1117/12.785427","DOIUrl":"https://doi.org/10.1117/12.785427","url":null,"abstract":"Ice made of ultrapure water or water doped with 1 % polymer (polyethylene glycol, \"PEG\") was irradiated by laser light with fluences between 2 and 80 J/cm2 in the ultraviolet (UV) regime at 355 nm and in the infrared (IR) regime at 1064 nm in vacuum. In the UV regime there is a threshold for plasma formation at 3.5 J/cm2, whereas the threshold is at 8.5 J/cm2 in the IR regime. The ions from the plasma plume were studied by a Langmuir probe. The ion yield was much higher for UV laser irradiation than for IR laser irradiation. The peak of the time-of-flight spectra comprises ions of velocity from 60 to 110 km/s. Generally, the ion yield was slightly larger for ice samples doped with PEG than for pure ones. The threshold behavior was much more pronounced in the IR regime than in the UV regime. These results indicate that the behavior of the plasma current can be understood in terms of ionization breakdown at the ice surface.","PeriodicalId":249315,"journal":{"name":"High-Power Laser Ablation","volume":"30 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2008-05-08","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"125971633","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
V. Tcheremiskine, O. Uteza, A. Aristov, M. Sentis, L. Mikheev
We report a novel experience gathered in the development of powerful optical sources of the vacuum ultraviolet (VUV) radiation, which are based on high-current multichannel surface discharges of submicrosecond duration. The peak intensity of the VUV radiation produced by the designed large-area (~0.1 m2) optical sources reaches 130 kW/cm2, whereas the intrinsic efficiency of the discharge emission within the spectral range of 120-200 nm attains 3.2 %. Application of such sources to pump a gaseous active medium of the multipass XeF(C-A) amplifier allows us obtaining the total gain factors exceeding 102 for the blue-green ultrashort optical pulses of 150 fs duration. The results presented in the report show a considerable potential of the developed laser technology for the femtosecond pulse amplification up to petawatt peak powers.
{"title":"Optical sources based on a multichannel surface discharge and their application to pump photolytically driven femtosecond XeF(C-A) amplifier","authors":"V. Tcheremiskine, O. Uteza, A. Aristov, M. Sentis, L. Mikheev","doi":"10.1117/12.782779","DOIUrl":"https://doi.org/10.1117/12.782779","url":null,"abstract":"We report a novel experience gathered in the development of powerful optical sources of the vacuum ultraviolet (VUV) radiation, which are based on high-current multichannel surface discharges of submicrosecond duration. The peak intensity of the VUV radiation produced by the designed large-area (~0.1 m2) optical sources reaches 130 kW/cm2, whereas the intrinsic efficiency of the discharge emission within the spectral range of 120-200 nm attains 3.2 %. Application of such sources to pump a gaseous active medium of the multipass XeF(C-A) amplifier allows us obtaining the total gain factors exceeding 102 for the blue-green ultrashort optical pulses of 150 fs duration. The results presented in the report show a considerable potential of the developed laser technology for the femtosecond pulse amplification up to petawatt peak powers.","PeriodicalId":249315,"journal":{"name":"High-Power Laser Ablation","volume":"10 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2008-05-08","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"131192412","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
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