J. F. Young

Generation of 1182‐Å radiation in phase‐matched mixtures of inert gases

Coherent radiation at 1182 A is obtained by third‐harmonic generation in a phase‐matched mixture of Xe and Ar. For generation from 3547 to 1182 A, Xe is negatively dispersive, and phase matching is obtained at a ratio of Xe:Ar=1:430. A conversion efficiency of 2.8% is obtained at an input power of 13 MW. As predicted by theory the conversion efficiency increases linearly to the limit of our available input power.

0.5-TW, 125-fs Ti:sapphire laser

We describe a terawatt, femtosecond laser system based on Ti:sapphire amplifiers and the technique of chirpedpulse amplification. The laser output at 807 nm contains 60 mJ of energy in a 125-fs pulse duration. The laser beam is nearly diffraction limited and may be focused to an intensity of 10(18) W/cm(2) with an f/6 optic.

Growth of High‐Quality LiNbO3 Crystals from the Congruent Melt

The use of LiNbO3 crystals in nonlinear optical experiments has been limited by the lack of long, high‐quality crystals. We have shown that crystals grown from a congruent composition melt are significantly less susceptible to birefringence variations which in the past have limited the useful phase‐matchable lengths of LiNbO3 crystals. Both a birefringence test which directly measures the spatial birefringence of the crystal and a second harmonic generation test were used to evaluate crystals grown from melts of various compositions. Crystals with less than 10−5 variation in birefringence over a length of 4 cm have been obtained repeatably when grown from congruent melts.

Retinal pigment epithelial cell function on substrates with chemically micropatterned surfaces

Model substrates with desired chemical micropatterns were fabricated using a microcontact printing technique. The substrate surfaces contained organized arrays of circular glass domains with a diameter of either 10 or 50 microm surrounded and separated by regions modified with octadecyltrichlorosilane (OTS) self-assembled monolayers (SAMs). The effects of surface patterning on in vitro cell attachment, proliferation, morphology, and cytoskeletal organization were evaluated using a human retinal pigment epithelium (RPE) cell line. Both micropatterns affected initial RPE cell attachment, limited cell spreading, and promoted the characteristic cuboidal cell morphology throughout the culture period. In contrast, RPE cells on plain glass control were elongated and appeared fibroblast-like prior to confluence. In addition, cells seeded at 30,000 cell/cm2 on the patterned surfaces maintained a normal pattern of actin and cytokeratin expression, and formed confluent monolayers within 4 days of culture. The cell density increased about 30-fold on both micropatterns by day 7. These results show that it is feasible to control RPE cell shape and expression of differentiated phenotype using micropatterned surfaces.

Infrared up‐conversion with resonantly two‐photon pumped metal vapors

We report efficient up‐conversion of low‐level ir radiation near 10 μ to the near ultraviolet. Radiation at 9.26 μ is converted to 3305 A with a photon conversion efficiency of 58% and a corresponding power gain of 16.2. The process employs resonant two‐photon pumping of the nonallowed 3s‐3d transition in Na.

Optical spectral amplitude CDMA communication

We report the first demonstration of bipolar coding techniques in the optical spectral domain for incoherent optical code division multiple access (CDMA) communication. Based on the modulation and detection principles that we have developed, the power spectrum of an erbium-doped superfluorescent fiber source was encoded using bipolar codes and decoded using an optical bipolar correlator. A CDMA testbed consisting of two encoders and one decoder was implemented with bulk optics and free-space transmission. Our measurements verify the correlations between the bipolar codewords and demonstrate the rejection of multiple access interference.

Limitation of 3547 to 1182 Å conversion efficiency in Xe

We report experiments which indicate that the 3547 → 1182A conversion efficiency in Xe-Ar mixtures is limited by Kerr-induced dispersion to about 0.9 percent. The mixed frequency third-order nonlinearity \chi^{(3)}(-3\omega, 3\omega, -\omega, \omega ) significantly alters the index of refraction at 1182 A in the presence of large power densities at 3547 A, affecting phase matching. We suggest using a Xe-Mg-Ar mixture to reduce the effect, thus permitting increased efficiencies.

Saturation of the Xe iii 109-nm laser using traveling-wave laser-produced-plasma excitation

We describe the construction and operation of a 109-nm, photoionization-pumped, single-pass laser in Xe III. The laser is pumped by soft x rays emitted from a laser-produced plasma in a traveling-wave geometry. Using a 3.5-J, 300-psec, 1064-nm laser pump pulse, we measure a small-signal gain coefficient of 4.4 cm(-1) and a total small-signal gain of exp(40). The laser is fully saturated and produces an output energy of 20 microJ in a beam with 10-mrad divergence.

Revisiting Low-Dose Total Skin Electron Beam Therapy in Mycosis Fungoides

PURPOSE Total skin electron beam therapy (TSEBT) is a highly effective treatment for mycosis fungoides (MF). The standard course consists of 30 to 36 Gy delivered over an 8- to 10-week period. This regimen is time intensive and associated with significant treatment-related toxicities including erythema, desquamation, anhydrosis, alopecia, and xerosis. The aim of this study was to identify a lower dose alternative while retaining a favorable efficacy profile. METHODS AND MATERIALS One hundred two MF patients were identified who had been treated with an initial course of low-dose TSEBT (5-<30 Gy) between 1958 and 1995. Patients had a T stage classification of T2 (generalized patch/plaque, n = 51), T3 (tumor, n = 29), and T4 (erythrodermic, n = 22). Those with extracutaneous disease were excluded. RESULTS Overall response (OR) rates (>50% improvement) were 90% among patients with T2 to T4 disease receiving 5 to <10 Gy (n = 19). In comparison, OR rates between the 10 to <20 Gy and 20 to <30 Gy subgroups were 98% and 97%, respectively. There was no significant difference in median progression free survival (PFS) in T2 and T3 patients when stratified by dose group, and PFS in each was comparable to that of the standard dose. CONCLUSIONS OR rates associated with low-dose TSEBT in the ranges of 10 to <20 Gy and 20 to <30 Gy are comparable to that of the standard dose (≥ 30 Gy). Efficacy measures including OS, PFS, and RFS are also favorable. Given that the efficacy profile is similar between 10 and <20 Gy and 20 and <30 Gy, the utility of TSEBT within the lower dose range of 10 to <20 Gy merits further investigation, especially in the context of combined modality treatment.

Third harmonic generation in phase‐matched alkali metal vapors

We report improvements in conversion efficiency for third harmonic generation in sodium and rubidium vapor. 30‐psec pulses of radiation at 1.064 μm have been converted to 0.3547 μm with an energy conversion efficiency of 10%. Factors limiting conversion efficiency are discussed.