Incubation/ablation patterning of polymer surfaces with sub-μm edge definition for optical storage devices

By exposure to low fluence UV laser radiation, the optical absorption coefficient of subsurface polymer material can be increased (incubation) with spatial control, using a suitable contact mask, proper imaging of the mask, or laser direct writing. Spatially selective ablation of polymethylmethacrylate (PMMA) is then achieved with large area XeCl excimer laser pulses at 308 nm. In this way, the transfer of spatial information to the material can be decoupled from the high laser fluence removal (ablation) step. The advantages are: The mask is exposed to only low fluence laser radiation — damage is avoided. Since the mask can be removed before the ablation step, mask contamination by the ablated plume cannot occur. Using this incubation/ablation method, PMMA surfaces can be patterned (248 nm/308 nm) with submicrometer spatial control and edge contrasts better than 0.2 m. This has impact on optical storage technology and laser surface processing techniques in general. The smallest single structure obtained was somewhat smaller than 0.5 m in diameter up to now, given by the mask.Presented at Laserion '91, June 12–14, 1991     

Measurement of Optical Constants of CVD-Diamond for Short-Wavelength Far-Infrared Lasers

A diagnostic system using short-wavelength far-infrared (FIR) lasers (40–70 m in wavelength) is now being developed for high density and large volume plasmas. In the wavelength region, a CVD-diamond is the excellent materials for optical windows of the laser and the plasma vessel and beam splitters of a multichannel interferometer. To design these optical elements, the optical constants (refractive index n, absorption coefficient and transmissivity T) of the CVD-diamond have been measured precisely by using FIR lasers of 48-, 57- and 71-m in wavelength. As an example, the result for 57.1511 m light is n = 2.383(1) ± 0.002, = 0.19 ± 0.05 cm^-1 and T = 97.5 ± 1.5% at 1.023 mm in thickness.     

Light absorption in laser-heated cavities

The absorption of laser light in 0.25–1 mm diameter gold cavities, irradiated for the purpose of generating high-temperature blackbody radiation with intense laser radiation of either =0.44 m or =1.3 m wavelength, was investigated. For =0.44 m radiation the absorption exceeded 0.9 for all conditions, but dropped to only 0.3 for the smallest cavities irradiated at =1.3 m. Entrance hole and cavity filling with plasma seems important for the understanding of the observations.     

Wavelengths for new CH3OH laser lines

Using a grating-tuned CO₂-TEA laser to pump CH₃OH in a metallic-wave-guide resonator, submillimeter laser emissions have been produced by pumping with 36 lines in the 9.4m CO₂ band and with 23 lines in the 10.6m band. Several dozen new SMM laser lines were observed. Wavelengths accurate to within 0.1% are given for 12 previously unmeasured lines between 34m and 225m.     

New cascade laser transitions in CH2F2 pumped with the 9R32 line of a cw CO2 laser

New cascade laser transitions of¹²CH₂F₂ at 172.50m, 208.83m, 220.44m, 223.99m and 250.61m are reported. A waveguide FIR laser was pumped with a quasi cw¹²C¹⁶O₂ laser operating on the 9R32 line. Together with the already known lines at 184.3m, 196.1m and 235.9m, the laser lines can be assigned to rotational transitions in the ₉ vibrational band of¹²CH₂F₂ and to refill transitions of the vibrational ground state ₀.     

The Optimum Operation of an Unified Mini-Optically Pumped NH3 Submillimeter Wave Laser

An unified miniature optically pumped NH₃ submillimeter wave laser (OPSMMWL), including a mini TEA-CO₂ pump laser, was developed. It lased successfully with coherent emission at 67.2m, 90.4m and 151.5m. The optimum operation of the unified mini-OPSMMWL was studied experimentally and the relations among SMMW laser output power, operating gas pressure, length and coupling condition of the cavity were measured. It has been found that buffer gas N₂ has significant effect on 67.2m and 151.5m emissions and very wide band SMMW laser emission was a common feature of the mini-OPSMMW cavity laser.     

FIR gain measurements in cw laser pumped CH3OD

Direct measurements of small signal and saturated gain in cw laser pumped CH₃OD are reported for three lasing transitions of 57 m, 82 m and 103 m. The 57 m transition has a measured gain of 0.6/m, the strongest gain in methanol reported so far. Moreover small gain saturation of this line makes it to be one of the strongest known cw FIR laser lines.     

Infrared detection by Tl?Ba?Ca?Cu?O superconducting films

The response of polycrystalline Tl–Ba–Ca–Cu–O superconducting thin films on short laser pulses has been investigated for radiation between 10 m and 500 m wavelength. Fast signals with time constants less than 1 ns were observed for wavelengths longer than about 100 m whereas for shorter wavelengths only a bolometric signal could be detected.     

Submillimeter emission lines from CD2Cl2 optically pumped lasers

Fifty-five new submillimeter laser lines from optically pumped CD₂Cl₂, have been obtained in a FIR metallic waveguide resonator. Twenty-seven lines, ranging from 184 m to 1387 m, and twenty-eight lines, from 219 m to 888 m, have been observed when using CW CO₂ laser and CW N₂O laser optical pumping, respectively. The accuracy of wavelength measurements are of the order of 3.10^–3.     

Pulsed laser crystallization of hydrogen-free a-Si thin films for high-mobility poly-Si TFT fabrication

The possibility to fabricate high-mobility polysilicon TFTs by nanosecond pulsed laser crystallization of unhydrogenated amorphous Si thin films has been investigated. Two types of lasers have been used: a large area ( 1 cm²) single ArF excimer laser pulse and a small diameter ( 100 m) frequency-doubled Nd:YAG laser beam, working in the scanning regime. Processed films have been characterized in detail by different optical and microscopic techniques. Device performances indicate that the best results are achieved with the excimer laser leading to high mobility values (up to 140 cm²/Vs) which are much larger than in polysilicon TFTs fabricated onto the same quartz substrates by low-temperature thermal (630° C) crystallization of amorphous Si films (_fe55 cm²/Vs).     

Excimer laser: a new tool for precision micromachining

The unique features of the pulsed UV light emitted by excimer lasers lead to a variety of innovative applications of this relatively new industrial laser type. The excimer laser is used for micromachining, surface treatment, microlithography and high-quality marking. The resolution of excimer laser processing is very high: typical structures of 100 m down to 0.2 m are produced. Moreover, typical ablation rates of about 0.1–1 m per laser pulse also allow extremely high precision in the depth of material removal.The most popular industrial applications of excimer lasers are microdrilling for highly integrated multichip modules (MCMs), TABs and FPCBs, in the manufacturing of nozzle plates for personal ink-jet printers, TFT annealing for flat panel displays, wire stripping for hard disk heads, and indelible marking for the aircraft, electronic and medical/health-care industries.In contrast to traditional and alternative methods, the use of excimer lasers allows fast and flexible production processes without pollution of the environment. Nearly all technical materials (plastics, ceramics, glass, metals, semiconductors, composites) and biological/medical materials can be processed by excimer laser methods.     

Gain dynamics of the 4.3 μm CO2 laser

A detailed study of the gain dynamics of the pulsed, optically pumped 4.3 m CO₂ laser is described. Small-signal gain coefficients as high as 14%/cm are measured in a 4.3 m amplifier using low-power pulses from a 4.3 m probe laser. The measurements are compared with a rate-equation model and good quantitative agreement is obtained. The model, which uses no adjustable parameters, is described in detail. Gain is studied as a function of optical pumping power, gas mixture, gas pressure and discharge excitation of the 4.3 m amplifier. Optimization of the gain is discussed.     

The refractivity of CO2 gas in the region of 10 μm

The refractivity of the CO₂ gas is measured with an experimental error of 2% in the 10-m region, using 10.4-m band CO₂ laser line. The frequency of the CO₂ laser is swept through the Doppler profile of the laser line. The experiment is achieved using a 0.63-m He–Ne/10.6-m CO₂-laser interferometer with a 2-m long vacuum cell. From the result, it is found that the Koch's formula also holds for the wavelengths in the 10-m region within an accuracy of 2%.     

A new procedure for thin-film deposition by solution spraying

The major reasons for the low photovoltaic efficiency of Cu₂S/CdS cells, in which the CdS film is deposited by spraying, are due to small film thicknesses which do not exceed 4 m and the small average grain size which ranges from 0.1 to 0.5 m.A new experimental solution spraying procedure is described that prevents both restrictions by controlling the substrate temperature. Average grain sizes of more than 1 m are obtained.Work supported by Ministere Pubblica Istruzione and Centro Regionale Ricerche Nucleari e di Struttura della Materia     

Tunable,narrow-band picosecond radiation in the mid-infrared by difference frequency mixing in GaSe and CdSe

We report on the generation of tunable, narrow-band picosecond laser pulses in the mid-IR at 1 kHz repetition rate. An optical parametric oscillator (OPO) seeded optical parametric amplifier (OPA) delivers signal and idler pulses with energies of several hundred microjoule tunable between 1.56 and 3.24 m. Difference frequency mixing of the OPA signal and idler waves permits the generation of mid-IR radiation between 3 and 24 m. The laser system therefore permits full coverage of the wavelength range between 1.6 and 24 m. Conversion efficiencies greater than 50% and pulse energies up to 40 J are obtained with GaSe. PACS 42.65.Re; 42.65.Yj; 42.72.Ai     

Width reduction of laser microdrillings by subsequent mechanically induced plastic deformation

This work reports a novel process combination, which is capable of forming large hole matrices (100 pores/mm²) in thin stainless steel foils (10 mfoil<300 m) maintaining high processing rates and pore widths smaller than 5 m. This technique perforates stainless steel foils with high-speed on-the-fly laser perforation (60000 drillings/min) followed by a cold-roll forming of the laser-treated foil. The cold-roll forming leads to a pore-size reduction (in one dimension) perpendicular to the rolling direction. For the laser processing a diode-pumped, q-switched and frequency-tripled Nd:YAG laser (=355 nm, =30 ns), and a flashlamp-pumped Nd:YAG laser (=1064 nm, =57 s) were applied. Using this process combination, minimum pore sizes of 3.5 m have been achieved. At present, the processing efficiency of cold-rolled percussion drillings inserted with nanosecond pulse durations is lower in comparison with single-pulse on-the-fly perforation, but in terms of quality (straight pore channel, low standard deviation of pore widths and pore widths smaller than 5 m) well suited for various fields in filtration (e.g. particle removal) . PACS  81.20.Hy; 42.62.Cf; 81.40.Ef     

Strong far-infrared laser action in carbonyl fluoride and vinyl fluoride

Intense far-infrared laser action is reported for carbonyl fluoride and vinyl fluoride. Eleven new lines with wavelengths between 339 m538 m were obtained by optically pumping carbonyl fluoride with numerous lines of the 10.4 m band of a cw CO₂ laser. Twenty-three lines with wavelengths in the range 172 m783 m were detected when pumping the recently discovered efficient FIR laser molecule vinyl fluoride. In addition, three very weak new lines were found using 1.1-difluoroethylen.     

Analysis of the effects of doping and barrier design on the small-signal modulation characteristics of long-wavelength multiple quantum well lasers

This theoretical work has modelled the small signal response of InGaAsP and InGaAlAs multiple quantum well (MQW) lasers based on an ambipolar carrier transport model. The MQW parameters such as barrier bandgap, barrier width and the number of quantum wells have been optimized for high-speed modulation. The effect of the p-type doping and the strain of the InGaAs well have also been investigated.For the InGaAsP-based system, the optimization for maximum 3 dB bandwitdth shows that the optimum width is about 5 nm for 1.1 m barriers and 7 nm for 1.2 m barriers. The optimum barrier bandgap wavelength is about 1.1 m for the barrier width of 6 nm, about 1.15 m for 8 nm and 10 nm barriers. The p-doped MQW exhibits a higher modulation bandwidth because of its high differential gain and improved carrier distribution among the MQWs. The compressively strained InGaAs quantum well system has the potential for a higher modulation bandwidth. For the InGaAlAs-based system, the optimization for maximum 3 dB bandwidth shows that the optimum width is about 4 nm for a barrier wavelength of 1.10 m, and 6 nm for 1.2 m. The optimum barrier bandgap wavelength is about 1.1 m for a barrier width of 4 nm, and about 1.2 m for 6, 8 and 10 nm.     

Fabrication and characteristics of double-fused vertical-cavity lasers

We discuss the fabrication process and characteristics of three consecutive runs of double-fused 1.5-m vertical-cavity lasers. We have measured light-current characteristics of over three hundred lasers with ten different diameters between 6 and 60 m and observe a yield of over 95%. The process and design improvements resulted in a low pulsed threshold current of 3 mA on a number of 6- and 8-m-diameter devices and threshold current density of 2 kA cm^–2 on 60-m-diameter devices at room temperature.     

Near Field Observation of a Refractive Index Grating and a Topographical Grating by an Optically-Trapped Gold Particle

We observed the near field for a refractive index grating fabricated on a planar light waveguide circuit (PLC) by scanning an optically-trapped 100 nm diameter gold particle. We demonstrate that stable trapping and scanning occur with a Gaussian laser beam at the scan velocity of 1.6 m/s and Nd:YAG laser power of 25mW. The scattered Ar laser light from the gold particle is strong at high refractive indexes of the grating with periods of 1.06 m and 0.53 m both by s and p polarized illumination. In addition, we observed the surface profile of the optical disk tracking groove with and without the gold particle. © 2004 The Optical Society of Japan