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Purpose: We validate the usefulness of laser-induced autofluorescence for the detection of bladder carcinoma.Materials and Methods: We obtained and analyzed fluorescence spectra from 75 patients in whom bladder cancer was suspected. Tissue fluorescence was excited by a nitrogen laser using a quartz optical fiber placed in gentle contact with the area of interest. The laser-induced autofluorescence spectrum was recorded using an intensified optical multichannel analyzer system. Spectra were corrected for the spectral response of the optical system, and the ratios of laser-induced autofluorescence intensities (I) at 385 and 455 nm. (I385/I455) were determined. We had previously established this ratio as a diagnostic algorithm. We included only suspicious bladder lesions (erythematous, edematous, raised and so forth) that were difficult to diagnose by cystoscopy as well as areas from which random biopsies were obtained. The fluorescence ratio algorithm was applied to 130 bladder areas.Results: Of the...

Purpose: We assessed the ability of laser induced autofluorescence to differentiate malignant from nonmalignant bladder lesions.Materials and Methods: We studied 53 patients with bladder cancer undergoing mucosal biopsies or transurethral resection of a bladder tumor. A quartz optical fiber was advanced through the working channel of a cystoscope and placed in gentle contact with the bladder. Tissue fluorescence was excited by 337 nm. light pulses (nitrogen laser). One fiber was used for transmission of the excitation and emission (fluorescence) light. An optical multichannel analyzer system was used to record fluorescence spectra of the sites of interest.Results: We analyzed the fluorescence spectra of 114 bladder areas (1 carcinoma in situ as well as 28 malignant, 35 inflammatory, 7 dysplastic, 1 squamous metaplastic and 42 normal areas). These lesions included 44 difficult to diagnose suspicious tumors (11 malignant and 33 nonmalignant). We developed an algorithm that used the I385:I455 nm. flu...

Background and Objective Surgical reconstruction of bony defects in the maxillofacial region involves fixation of bony fragments with mini and micro plates. Bone stabilization during hole drilling is often challenging due to the need to apply pressure when using a conventional mechanical Hall drill. In addition, fragmentation of the fragile bones may occur and complicate the reconstruction. The pulsed Er:YAG laser offers an attractive alternative drilling modality because it does not require physical contact with the bone in order to drill holes, cuts bone with minimal thermal damage, and allows precise control of bone cutting. The objective of this study was to investigate the pulsed Er:YAG laser as an alternative to the mechanical bur by comparing bone healing using both modalities. Study Design/Materials and Methods Bone healing in an inferior border defect of the rat mandible was examined using either an Er:YAG laser or a mechanical but for drilling. The healing of osteotomies in facial bones and of screw holes for plate stabilization of free bone fragments was studied. Results All defects healed by 4 weeks postoperatively. Histologic evaluation demonstrated no difference in the amount of newly formed woven bone at the osteotomy site or screw holes made by either the laser or the drill. The extent of thermal damage at the osteotomy sites was comparable in laser and mechanically cut bone fragments. Conclusions On the basis of this study we suggest that the Er:YAG laser can be used clinically in thin, fragile bones in the maxillofacial region. © 1996 Wiley-Liss, Inc.

The ablation thresholds and patterns of collateral damage in cornea produced by Er:YAG (2.94 microns) and Er:YSGG (2.79 microns) lasers were measured. Two different pulse durations, 200 microseconds (normal spiking mode) and 100 ns (Q-switched mode), were used at both wavelengths. In the normal spiking mode, damage zones of 16 +/- 2 microns and 39 +/- 7 microns and ablation thresholds of 250 +/- 20 mJ/cm2 and 420 +/- 35 mJ/cm2 were measured at 2.94 microns and 2.79 microns, respectively. In the Q-switched mode, damage zones of 4 +/- 2 microns and ablation thresholds of 150 +/- 10 mJ/cm2 were found irrespective of the laser used. The similarity between the results using the Er:YAG and Er:YSGG lasers in the Q-switched mode suggest that either laser can be used with equal effectiveness for corneal trephination.

We investigate shock waves generated by excimer laser ablation of sheet polyimide confined in water. The velocities of the ablation-induced pressure waves in the water are determined by an optical probe system. We measure supersonic velocities up to a few hundred microns away from the irradiated surface, indicating the formation of shock waves. We use these velocities to calculate the corresponding pressures. They are already in the kbar range at fluences comparable to the threshold of ablation. The shock pressure varies as the square root of the incident laser fluence, a behavior that is explained by the rapid heating of the confined gaseous products of ablation. The initially planar shock waves propagate, become spherical, and decay within a few hundred microns in the surrounding water to acoustic waves. During spherical expansion the shock pressure drops as the inverse of the square of the propagation distance. The shock waves generated may be relevant in explaining photoacoustic damage observed in biological tissue after excimer-ablation at corresponding irradiances. They may also be important in material processing applications of excimer laser ablation of polymers as they can lead to plastic deformation.

Human liver manganese superoxide dismutase has been purified by a short procedure that includes a tri-phase partitioning step to provide materials that can be crystallized from ammonium sulfate. X-ray diffraction studies at 3 A resolution show that the crystals belong to the hexagonal space group P6122 or P6522, with cell dimensions a = b = 81.1 A , c = 242.2 A . Manganese superoxide dismutase levels as determined by enzymatic assay as well as by enzyme-linked immunosorbent assay indicated that considerable variations occur in different livers but the total superoxide dismutase activity (Mn superoxide dismutase plus Cu,Zn superoxide dismutase) seems to be kept at constant values.

The dynamics of tissue ablation using an Er:YAG laser were studied using flash photography and optical pump-probe techniques. Both normal-spiking-mode and Q-switched Er:YAG laser radiation were used to study the ablation of skin and bone. Time-resolved photographs of the ablation plume were obtained using a microscope-mounted camera together with pulsed illumination from an excimer-pumped dye laser. The velocity of the plume front, obtained from the photographs, was approximately 1400 m/s. The same velocity was also measured using an optical pump-probe technique. Both techniques indicate that material removal occurred after the end of the 90-ns-long Q-switched laser pulse and that each micropulse in the normal-spiking-mode pulse train was capable of ablating and rapidly ejecting tissue.

The wavelength dependence of the ablation threshold of a variety of tissues has been studied by using a tunable pulsed Co:MgF2 laser to determine how closely it tracks the optical absorption length of water. The Co:MgF2 laser was tuned between 1.81 and 2.14 microns, a wavelength region in which the absorption length varies by a decade. For soft tissues the ablation threshold tracks the optical absorption length; for bone there is little wavelength dependence, consistent with the low water content of bone. Thermal damage vs. wavelength was also studied for cornea and bone. Thermal damage to cornea has a weak wavelength dependence, while that to bone shows little wavelength dependence. Framing-camera pictures of the ablation of both cornea and liver show explosive removal of material, but differ as to the nature of the explosion.

Formation of cyclobutylpyrimidine dimers and strand breaks in double-stranded DNA was investigated by using 532-nm, 28-ps pulses from a frequency-doubled, mode-locked Nd:YAG laser at intensities below and above the threshold for optical breakdown. Two-photon absorption by DNA was detected in the absence of optical breakdown by measuring the yields of cyclobutylpyrimidine dimers formed in supercoiled pBR322 DNA. The yield of cyclobutylpyrimidine dimers per laser pulse was measured at seven peak intensities between 1.03 and 8.04 GW/cm{sup 2}. A plot of the ln (dimer yield/pulse) versus ln (photon flux) was linear with a slope of 1.88 {plus minus} 0.26. The two-photon cross section for absorption at 532 nm was calculated to be 0.5 ({plus minus}0.2) {times}{sup {minus}52} cm{sup 4} s photon{sup {minus}1} per nucleotide. Experiments performed by using intensities above the threshold for optical breakdown caused breaks in the DNA strands but no cyclobutylpyrimidine dimers. The free-radical quencher, mannitol, partially inhibited formation of the strand breaks, indicating that the mechanical processes initiated by the plasma also contribute to the creation of DNA strand breaks.

The mechanisms responsible for the generation of stresses by pulsed-laser energy deposition in solids are elucidated with special attention given to laser-tissue interactions. These mechanisms include thermal expansion, subsurface cavity formation, ablative recoil and plasma formation and expansion. Scaling laws are presented for the magnitude of the stresses generated by each of these processes. The effect of laser parameters and material properties on the magnitude and temporal behavior of the stress transients is considered. The use of these scaling laws in conjunction with measurement of stress transients induced by pulsed laser sources may be a powerful tool in determining the physical processes which control the response of materials to pulsed energy deposition. In addition, the controlled generation and accurate measurement of acoustic transients may have important diagnostic and therapeutic applications.

Medical applications of laser-induced fluorescenceKevin T. Schomacker, Joan K. Frisoli,Thomas F. Deutsch,Massachusetts General HospitalBoston, MA 021141. INTRODUCTIONAlthough lasers have traditionally been used in medicine as therapeutic devices,there has been considerable interest in using them as diagnostic tools. A numberof groups have been studying the medical applications of Laser-InducedFluorescence (LIF)1'2. We describe three projects examining the potential use ofLIF in medicine. They involve the classification of colonic polyps, the LIF-.guided resection of brain tumors, and the advantages of LIF for studyingphotosensitizer pharmacokinetics. All three projects are only summarized;complete descriptions will appear elsewhere.2. LASER-INDUCED AUTOFLUORESCENCE OF COLONIC TISSUE:BASIC BIOLOGY AND DIAGNOSTIC POTENTIALRecently, several groups have used LIF to diagnose premalignant colorectallesions, i.e., to distinguish adenomatous polyps from normal colonic tissue andhyperplastic polyps3'4. Hyperplastic polyps are non-neoplastic lesions caused bythe failure of mature epithelial cells to detach normally. Adenomatous polypsare benign hyperproliferative neoplasms consisting of immature, poorly-differentiated epithelial cells with differing degrees of dysplasia. The vastmajority of colorectal carcinomas arise from adenomatous polyps.This study had three goals: 1) to evaluate the feasibility of using LIF to detectcolonic neoplasia and, in particular, to distinguish adenomatous from hyperplasticpolyps in vivo; 2) to test the transportability of published algorithms forevaluating our colonic LIF and 3) to examine the LIF spectra ofdifferent colonic tissue types along with spectral changes with time afterresection and relate the changes to the biology and structure of the tissue. Amore quantitative understanding of these spectral changes with tissue type wasobtained by decomposing the fluorescence spectra into the contributions ofindividual tissue components (fluorophores and absorbers). This spectraldecomposition approach was also used to quantify the differences between in vivoand in vitro LIF spectra as well as the changes in the observed in vitro spectraas a function of time after resection. In addition, the depth to which the LIFmeasurement probes was estimated from measurements of fluorescence intensity offrozen sections as a function of tissue thickness. Finally, the entire study usedcolonic polyps as a model system for understanding the potential and limitationsof autofluorescence for tissue diagnosis. Only the diagnostic potential will bedescribed here.The LIF system is shown schematically in Figure 1. The output of a pulsed-nitrogen laser (337 nm, 3-ns pulses at 10 Hz and 200-jzJ pulse energies) wascoupled via a quartz lens into a single 600-jLm-core-diameter quartz optical fiber.Typical energies delivered to tissue were 40 jzJ. Fluorescence from the tissue wastransmitted through the same optical fiber and optically coupled to a quartz

We measure the stress transients resulting from pulsed excimer laser irradiation of polyimide at 351, 308, 248 and 193 nm, using thin (9 μm) piezoelectric PVDF (polyvinylidene fluoride) films. We find that fluences between 3·10−3 and 102 J/cm2 generate peak stresses between 104 and 109 Pa. Further, the results show three ranges of fluence where different physical mechanisms mediate the stress generation. In the lowest range of fluence, subsurface thermal decomposition (for λ = 351 and 308 nm) and photodecomposition (for λ = 248 and 193 nm) govern the generation of the observed stresses. At higher fluences we identify two regimes, independent of laser wavelength, where the gas dynamic expansion of the ablation products and plasma formation and expansion, are responsible for the generated stresses.

Cyclobutylpyrimidine dimers were detected in double-stranded plasmid DNA after exposure to 532-nm 28-ps pulses at intensities (1-8 GW/cm2) below the threshold for optical breakdown. Formation of these photoproducts was attributed to simultaneous two-photon absorption by nucleotides in DNA because the rate of dimer formation was dependent on the square of the intensity and because an equivalent number of photons at 514 nm delivered at low intensity did not produce dimers. The average two-photon cross-section at 532 rim for absorption by a nucleotide was found to be 0. 50 ( 0. 02) x l052 cm4sec'' photon* Intensities of 532-rim radiation above the threshold for optical breakdown caused DNA strand breaks by radical and mechanical mechanisms. 1 .

The use of pulsed infrared lasers for tissue ablation has led to increased control over thermal damage to tissue and to more precise control over material removal. Tissue removal is mediated by the explosive vaporization of water, which can lead to clinically significant tissue effects.

A pump-probe technique was used to measure the shock wave velocity generated by laser-induced optical breakdown in water. The transient shock pressure field was mapped using the measured shock velocities, together with the equation of state of water and the jump equations. We find that the calculated shock pressures near the breakdown region are in the kbar range and scale as hr2. Depending upon the energy of the laser pump pulse, typically 3 to 15 mJ, the shock wave dissipates within 300-500 1um.

The use of high peak power laser pulses in the short and ultrashort time domains has opened a variety of novel laser-tissue interactions with potential for application in clinical medicine. Photodisruption (optical breakdown) of nominally transparent tissues within the eye, excimer laser tissue ablation, and femtosecond laser tissue ablation are three examples of such tissue effects. Laser tissue interactions in these time domains will be reviewed and selected techniques for investigation of the time scale and damage mechanisms of these interactions will be presented.

Infared-infrared double resonance measurements of the ν 3 absorption band of SF 6 using a CO 2 TEA pump laser (0.3 J/cm 2 maximum excitation) and a cw CO 2 probe laser have been carried out. These measurements probe both the coherent and quasi-continuum phases of the multiphoton dissociation process in SF 6 . The spectral and temporal dependences of the induced absorption are obtained. The results give the first direct measurement of collisionless intramolecular vibrational energy redistribution times in a vibrationally excited complex molecule; for an excess energy of three quanta deposited in the ν 3 mode of SF 6 , the ν 3 mode comes into equilibrium with all the remaining vibrational degrees of freedoom with a 3 ± 1 μs time constant.

Tissue removal by infrared lasers is accompanied by thermal damage to nonablated tissue. The extent of thermal damage can be controlled by a choice of laser wavelength, irradiance, and exposure duration. The effect of exposure duration has been studied in vivo by using CO2 lasers with pulse widths that vary from 2 microseconds to 50 msec. Pulse widths of 50 msec, typical of a shuttered, continuous-wave CO2 laser, produce damage regions 750 micron wide in normal guinea pig skin; the use of a 2-microseconds-long pulse reduced this damage zone to as little as 50 micron. Using 2-microseconds-long pulses, in vitro studies showed that the minimum zone of thermal damage varied significantly with tissue type. The thermal denaturation of these tissues has been studied and correlated with damage. The effect of denaturation temperature and pulse duration on the width of the damage zone is explained by a simple model.

The pulsed ultraviolet excimer laser has been used to produce tissue ablation with a high degree of precision and with minimal thermal damage to adjacent structures. In comparative studies of excimer laser ablation of the cornea and crystalline lens using 193 nm and 248 nm radiation, threshold fluence for corneal and lens ablation was higher at 248 nm than at 193 nm. Ablation of corneal stroma at 193 nm produced the most precise cuts. When examined by transmission electron microscopy, a narrow zone of damaged tissue (0.1 to 0.3 micron) was seen immediately adjacent to the tissue removed by the laser. Ablation with 248 nm radiation produced incisions with ragged edges and with a wider and more severe zone of damage in adjacent stroma. Ultraviolet spectral transmission studies of the corneal stroma showed that absorption is 10 times greater at 193 nm than at 248 nm. The excimer laser was effective in producing well controlled ablation of the crystalline lens in vitro, with effects parallel to those seen in the cornea.

A technique for maskless writing of metal films with submicrometer dimensions is described. An ultraviolet beam from a cw or pulsed laser is used to photodissociate an organometallic gas near a gas–solid interface. The liberated metal atoms then condense in an area of dimensions comparable to the laser spot size. Experiments which elucidate the essential physics of the process have been performed.

Laser-controlled chemical reactions are being explored for use in all phases of the processing of semiconductor devices. Laser-induced chemical processing can produce submicrometer features without the aid of photolithography. Research is also providing new information on light-excited and light-enhanced interface reactions.

We studied the use of a short-pulse, flashlamp-pumped dye laser, emitting at 666 nm, to create ab interno sclerotomies in cynomolgus monkeys using a fiberoptic delivery system. Because of the low optical absorption of the sclera in the visible portion of the spectrum, ablation of sclera by continuous wave lasers emitting in this region requires high energies and produces significant thermal damage to surrounding tissues. To enhance the optical absorption of sclera, methylene blue dye was applied iontophoretically; patent sclerotomies were obtained in all 10 eyes of six cynomolgus monkeys, with energies ranging from 15 to 50 mj/pulse. Thermal damage to the adjacent sclera was confined to 300 microns. Complications included mild intraoperative hyphema at all pulse energies and iridodialysis at higher pulse energies. Filtration blebs routinely failed within 7 days; the use of 5-fluorouracil postoperatively significantly prolonged bleb duration. The small incision technique described allows ab interno sclerotomies to be created with low pulse energies without the need for conjunctival dissection, thereby avoiding the problems associated with conjunctival wounds. An advantage of this technique is that it can be modified to create ab interno sclerotomies noninvasively by delivering pulsed visible radiation through the cornea with a gonioscopic-slitlamp system.

The effects of picosecond laser-induced optical breakdown on tissue were investigated using high-intensity 40 ps Nd:YAG laser pulses at 1.06 microns. Tissue damage was evaluated using the corneal endothelium in vitro as a model system. Systematic studies were performed to determine the scaling of the tissue damage and damage range with pulse energy. For suprathreshold lesions, the radius of the damage zone varies as the cube root of the pulse energy, in agreement with simple physical scaling laws. A minimum damage range of less than 100 microns was observed for pulse energies of 8 muJ. Damage morphology was investigated by scanning electron microscopy. Three different damage patterns were observed; cell damage, cell removal, and rupture of Descemet's membrane. Different irradiation geometries were used to study damage mediated by either the shock wave or the cavitation bubble. Comparative studies using 10 ns pulses demonstrated that picosecond pulses yielded a significant reduction in collateral tissue damage.

• Laser endophotocoagulation is an important technique in vitreoretinal surgery. We performed successful retinal endophotocoagulation in the eyes of Dutch-belted rabbits, using high-power phased-array semiconductor lasers, emitting at 808 and 817 nm. The laser itself measured 25 × 30 × 21 mm, was air cooled, and was portable. At a treatment power of 100 mW, uniformly white photocoagulation lesions were seen at exposure durations of 0.2 to 1.0 s. Lesions were similar in appearance to argon laser photocoagulation lesions, as determined by ophthalmoscopy and fluorescein angiography. Thin-section histologic examination of acute lesions revealed injury localized to the outer retina; chorioretinal scar formation was noted ten days after photocoagulation. To our knowledge, this study is the first in which therapeutically useful lesions were produced using a diode laser and demonstrates the feasibility of using these highly efficient and compact laser sources for ophthalmic photocoagulation.

Laser endarterectomy, a promising new method of reopening stenotic or occluded arteries, has been limited by difficulties in ablating calcified plaque. This study demonstrates that pulsed, visible laser radiation (482 nm, 1 μs duration, 40-80 mJ/pulse) can ablate calcified plaque at intensities (50 MW/cm2) that are readily transmit, ted down flexible (320 μm diameter) optical fibers and at fluences which are below the threshold for ablating normal artery. The ablative process is characterized by a loud snapping sound, a luminescent plume, ejection of fine debris, and an ablation efficiency as high as 10 mg/J, suggesting that removal of material occurs primarily by formation of a plasma and fracturing of the plaque, rather than by thermal vaporization. The presence of a plasma associated with ablation of calcified plaque was documented by emission spectrum measurements.

Picosecond optical breakdown was investigated in order to assess its potential for performing highly localized incisions for laser surgery. Measurements of breakdown were performed using single 40-ps Nd: YAG laser pulses in distilled water. Novel optical pump-probe techniques were developed to characterize the transient spatial and temporal dynamics of the plasma, shock wave, and cavitation phenomena which are associated with the breakdown. The maximum cavity radius and the shock wave zone are shown to scale as the cube root of the pump pulse energy over almost three orders of magnitude. For pulse energies close to the threshold energy of 8 μJ, the shock range was ∼100–200 μm and the cavity radius was 140 μm. Complementary experiments were performed with 10-ns pulse durations. Since picosecond pulses have high peak intensities with low pulse energies, a significant enhancement in localizability may be achieved. The implications for ophthalmic microsurgery are discussed.

Both linear and infrared—infrared double resonance measurements of the ν 3 absorption band of SF 6 dissolved in liquid O 2 and Ar are reported. Saturation measurements of the infrared absorption give a V—T relaxation time of 27 ± 7 ps in liquid O 2 and 160 ± 40 ps in liquid Ar. The unique features of the spectroscopy of complex molecules in simple liquid hosts offer potential advantages for laser photochemistry.

A focused, ultraviolet (UV) laser beam has been used to produce micrometer-sized chemical processes on solid surfaces. These processes are initiated by the photodissociatlon of a molecular gas in the vicinity of the gas-solid interface. Depending on whether the active photofragment reacts with or is adsorbed on the solid, microetching or microdeposition occurs. Both the surface properties of the solid and the gas-phase kinetics contribute to the process localization. Metal alkyls and methyl halides have been used as parent molecules for deposition and etching, respectively. A focused, 3 mW UV laser is sufficiently intense to produce satisfactory rates for both processes. Several applications of this small-scale photochemistry to microelectronics have been investigated.

The fragmentation of gallstones and kidney stones using pulsed visible laser radiation has recently been demonstrated; however, the fragmentation mechanism is not well understood. The temporal and spectral characteristics of the bright flash of light accompanying fragmentation of gallstones were studied using 0.8 and 360-μs-long, 690-nm-wavelength, dye-laser pulses. Time-resolved visible emission spectra show a broad continuum upon which line spectra are superimposed. The continuum emission is due to free-free and free-bound electron transitions indicative of a plasma and the line spectra are due to neutral and ionized calcium. Initiation of this plasma is fluence rather than intensity dependent. A model is proposed in which laser energy is coupled to the plasma, which then impulsively expands, generating intense acoustic transients which fracture the stone.

Ablation of human atheromas with laser pulses that had only a small effect on normal artery tissue was shown in vitro in air and under saline using 1-mu sec pulses at 465 nm from a flashlamp-excited dye laser. At this wavelength, there is preferential absorption in atheromas due to carotenoids. The threshold fluence for ablation was 6.8 +/- 2.0 J/cm2 for atheromas and 15.9 +/- 2.2 J/cm2 for normal aorta tissue. At a fluence of 18 J/cm2 per pulse, the ablated mass per unit of energy ranged from 161 to 370 micrograms/J for atheromas and from 50 to 74 micrograms/J for normal aorta tissue. Ablation products consisted of cholesterol crystals, shredded collagen fibers, and small bits of calcific material. Most debris was less than 100 micron in diameter, but a few pieces were as large as 300 micron. High-speed photography of ablation in air suggested explosive ejection of debris, caused by vapor formation, at speeds on the scale of 300 m/sec. Histological analysis showed minimal thermal damage to residual tissue. These data indicate that selective laser ablation of atheromas is possible in vitro.

The use of lasers in medicine began soon after the first ruby laser was invented in 1960. In recent years the number and variety of applications of lasers to biology and medicine has been increasing rapidly. I will review some of these applications, with emphasis on the physical mechanisms and the technology. After an overview of the various types of laser‐tissue interactions, I give some examples of how these interactions are exploited in medicine.

High-speed flash photographs of laser-induced fragmentation of biliary and renal calculi under water were obtained using one-microsecond-long dye-laser pulses for both illumination and ablation. The photographs show the presence of a bubble with irregularities on the surface that suggest the early presence of debris or microbubbles. Fragmentation occurs before the bubble collapses, suggesting that fragmentation is due to laser-induced acoustic transients rather than to collapse of a laser-induced cavitation bubble.

The laser window problem is reviewed with emphasis on failure mechanisms, absorption processes, and material evaluation. Failure by thermal fracture and by optical distortion is discussed and the material parameters needed to calculate figures of merit for these failure modes are tabulated for a variety of materials. The exponential dependence of absorption coefficient on wavenumber for intrinsic multi-phonon processes is discussed and its use in discriminating extrinsic from intrinsic absorption emphasized. Laser calorimeter absorption measurements at 10. 6 Μm and 5. 25 Μm are described and the measured values tabulated. The use of internal reflection spectroscopy to examine the effect of various surface treatments on

It is shown that planar dipole and quadrupole magnetic fields can be obtained by means of line currents, and that with suitable geometries homogeneous dipole fields and constant-gradient quadrupole fields can be produced. Expressions are derived for the magnetic field of a quadrupole lens having coils of annular sector geometry.

Crystalline ceruloplasmin may be readily prepared in good yield from human serum or plasma by procedures based on chromatography on diethylaminoethyl-cellulose. As prepared, this protein appears to be made up of a series of molecules of varying solubilities. Repeated crystallization followed by a Chromatographic separation step at neutral pH provides a ceruloplasmin containing 8 atoms of copper per 150,000 g. protein and one that shows a single component on electrophoretic and ultracentrifugal assay.

The performance of N2–CO2–He lasers operating at pressures in the 10–120‐Torr range and with nitrogen flow rates of 20–90 standard liters per minute is discussed. A 10‐cm‐long, 13.5‐mm‐i.d. discharge tube produced 140‐W output power. These lasers operate as in‐line mixing lasers, producing about one photon per excited nitrogen molecule. Cooling is provided by rapid removal of hot gas from the discharge region.

Rabbit antibody to apoceruloplasmin has been used to demonstrate that two forms of ceruloplasmin occur in serum. In addition to the well known blue protein, a colorless component was found. The latter protein lacks oxidase activity, has a relatively low copper content, and is immunologically similar to apoceruloplasmin. It constitutes from 10 to 20% of the total ceruloplasmin found in normal serum. The electron paramagnetic resonance spectra of ceruloplasmin and its antibody precipitate were found to be identical. Therefore, antibodies could be used to isolate ceruloplasmin from serum for electron paramagnetic resonance studies. An antibody precipitate of all of the ceruloplasmin from a sample of serum contained two species of paramagnetic copper. The colorless ceruloplasmin appears to contain the type of copper which gives an electron paramagnetic resonance signal with a broad hyperfine structure.

A delay line was discharged into a terminating resistor by a spark gap of coaxial design. The spark gap was triggered by a focused laser beam, introduced along the axis; a Q-switched ruby laser giving pulses of 20 ns duration and up to 50 MW power was used. The range of operation of the gap, formative time of the breakdown and jitter were investigated for different gases at pressures above atmospheric, gap widths of 4-10 mm and voltages of up to 120 kv. Mixtures of argon and nitrogen were found to have certain advantages, such as a low threshold for ionization by the laser beam, sufficient dielectric strength, low values of the formative-time jitter and chemical inertness. Formative times of down to about 1 ns and jitters below 1 ns were found. The laser power can be relatively low (0·5-5 MW). An explanation for the breakdown mechanism is proposed.

Dye solution lasers are observed to lase at shorter wavelengths when laser pumped than when flashlamp excited. A comparison of the computed frequency‐ and time‐dependent gains for the two pumping methods explains this behavior and the observed Q dependence of the lasing frequency. This treatment also suggests a new technique for frequency tuning dye lasers.

The direct doping of InP with variable Cd concentrations has been demonstrated in a maskless process with micrometer‐scale spatial control. The process makes use of cw UV‐laser photodeposition of the dopant on a laser‐heated surface.

Ultraviolet laser photolysis of methyl‐halides has been used to produce localized photoetching of GaAs and InP. A spatial resolution of ≃1μm has been achieved and an etch rate ≳104 times that of the dark reaction demonstrated. A chemical mechanism is proposed and the observed resolution is explained by a simple physical model.

Photodissociation of a thin surface layer of metal‐alkyl molecules with a UV laser is shown to be an effective technique for predisposing the irradiated region to subsequent film growth. The efficacy of this technique, termed ’’prenucleation,’’ can be understood using a simple mathematical model for the early stages of thin‐film formation. The technique has applications in direct writing of microstructures.

An Ar‐ion laser has been used to activate surface pyrolytic deposition of polycrystalline Si in a several micrometer reaction zone. Controlled doping with boron during deposition allows one‐step direct writing of highly conducting Si lines with linewidths as small as 1 μm. An unexpectedly fast deposition rate is associated with changes in the reaction kinetics as the dimensions of the reaction volume are reduced to microscopic lengths.

High‐resolution etching of single‐crystal and polycrystalline silicon has been demonstrated using an argon‐ion laser to control microscopic chemical reactions. Gas‐phase Cl2 or HCl is used in reactions initiated both by surface heating and by molecular photolysis. Features smaller than 5 μm and etch rates greater than 6 μm/s have been obtained. The process seems immediately suitable for a variety of problems in integrated‐circuit fabrication.

Laser-beam profile is an important laser parameter that is frequently ignored because conventional measurement techniques are cumbersome. A technique for accurately and rapidly measuring laser-beam profile with a commercial video camera and oscilloscope is described. Both two-dimensional pictures of the beam and quantitative, one-dimensional beam profiles can be obtained. The technique is particularly well suited for biomedical applications because it is compatible with most pulsed and continuous wave visible lasers, it uses readily available and relatively inexpensive components, and it is easy to implement.

The electrical properties of single‐crystal and amorphous Si, doped using a pulsed UV laser, have been studied as a function of laser wavelength and fluence and of UV dose. BCl3 or PCl3 parent gases were used to provide B or P dopant atoms. Dissociation of molecules adsorbed on the Si surface can supplement photolysis of gas‐phase molecules as a source of doping atoms.

A new technique for controlled etching of micrometer‐size regions on thin films has been developed. Dopant atoms are deposited on the film surface by UV laser photodissociation of a gas and incorporated by simultaneous heating with a visible laser beam. The process has been demonstrated by laser alloying Al films with Zn to produce localized chemically reactive regions of Zn/Al alloy.

An ArF excimer laser has been used to form p‐n junctions in Si. The laser produces dopant molecules by gas‐phase photolysis of an organometallic molecule and simultaneously heats the substrate to allow incorporation of the dopant. Solar cells having conversion efficiencies of 9.6% at AM1 without the use of antireflection coatings have been fabricated from these junctions.