Background and Objectives: We introduce and clinically examine a new concept of skin treatment called fractional photothermolysis (FP), achieved by applying an array of microscopic treatment zones (MTZ) of thermal injury to the skin. Study Design/Materials and Methods: Two prototype devices emitting at 1.5 mm wavelength provided a pattern of micro-exposures with variable MTZ density. Effects of different MTZ densities were tested on the forearms of 15 subjects. Clinical effects and histology were assessed up to 3 months after exposure. Treatment of photoaged skin on the periorbital area in an additional 30 subjects receiving four treatments over a period of 2-3 weeks was also tested. Tissue shrinkage and clinical effects were assessed up to 3 months after treatment. Results: Pattern densities with spacing of 250 mm or more were well tolerated. Typical MTZ had a diameter of 100 mm and penetrated 300 mm into the skin. Reepithelialization was complete within 1 day. Clinical effects were assessed over a 3-month period. Histology at 3 months revealed enhanced undulating rete ridges and increased mucin deposition within the superficial dermis. Periorbital treatments were well tolerated with minimal erythema and edema. Linear shrinkage of 2.1% was measured 3 months after the last treatment. The wrinkle score improved 18% (P < 0.001) 3 months after the last treatment. Conclusions: FP is a new concept for skin restoration treatment. Safety and efficacy were demonstrated with a prototype device. Further clinical studies are necessary to refine the optimum parameters and to explore further dermatological applications.

Spatially confined foci of thermal effects can be achieved by focusing a low-power infrared laser into skin. Size, depth, and density of microscopic, thermal damage foci may be arbitrarily controlled while sparing surrounding tissue. This may offer a new approach for nonablative laser therapy of dermal disorders.

Background and Objectives:We examined the effects of pulse energy variations on the dimensions of microscopic thermal injury zones (MTZs) created on human skin ex vivo and in vivo using nonablative fractional resurfacing. Materials and Methods: A Fraxel 1 SR laser system emitting at 1,550 nm provided an array of microscopic spots at variable densities. Pulse energies ranging from 4.5 to 40 mJ were tested on human abdominal skin ex vivo and in vivo. Tissue sections were stained with hematoxylin and eosin (H&E) or nitro blue tetrazolium chloride (NBTC) and MTZ dimensions were determined. Ex vivo and in vivo results were compared. Dosimetry analyses were made for the surface treatment coverage calculation as a function of pulse energy and collagen coagulation based on H&E stain or cell necrotic zone based on NBTC stain. Results: Each MTZ was identified by histological detection of a distinct region of loss of tissue birefringence and hyalinization, representing collagen denaturation and cell necrosis within the irradiated field immediately, 1, 3, and 7 days after treatment. At high pulse energies, the MTZ depth could exceed 1 mm and width approached 200 mm as assessed by H&E. NBTC staining revealed viable interlesional tissue. In general, no statistically significant difference was found between in vivo and ex vivo depth and width measurements. Conclusions: The Fraxel 1 SR laser system delivers pulses across a wide range of density and energy levels. We determined that increases in pulse energy led to increases in MTZ depth and width without compromising the structure or viability of interlesional tissue. Lasers Surg.

No abstract

Basal plane sapphire is a common substrate for the heteroepitaxy of GaN. This presents a challenge for fabrication of cleaved-facet GaN lasers because the natural cleavage planes in (0001) α-Al2O3 are not perpendicular to the wafer surface. This letter describes a method for achieving perpendicular cleaved facets through wafer fusion that can potentially be used to fabricate GaN based in-plane lasers. We demonstrate successful fusion of GaN to InP without voids or oxide at the interface and fabricate optically flat cleaved GaN facets that are parallel to the crystallographic planes of the host InP. I–V measurements have been performed across the n-N fused interface. These results show that the fused junction exhibits a barrier of several electron volts for electrons passing from the InP to the GaN and ohmic conduction of electrons moving in the opposite direction.

The MOCVD growth of InGaN / GaN multiple quantum well (MQW) structures for optoelectronic applications has been investigated. The structural and optical properties of the layers have been characterized by x-ray diffraction and photoluminescence. The effect of barrier and well dimensions on the optical properties have been examined; highest emission intensity and narrowest linewidth were obtained with thin wells (20–30 Å) and thick barriers (greater than 50 Å). By incorporating an MQW structure as the active region in a GaN p-n diode, high-brightness light emitting diodes (LEDs) have been produced. Under a forward current of 20 raA, these devices emit 2.2 mW of power corresponding to an external quantum efficiency of 4.5%. The emission spectrum peaks at 445 nm and exhibits a narrow linewidth of 28 nm. Under pulsed high current conditions, output power as high as 53 mW was realized and the peak emission wavelength shifted to 430 nm.

Room-temperature (RT) pulsed operation of blue (420 nm) nitride-based multiquantum-well laser diodes grown on a-plane and c-plane sapphire substrates has been demonstrated. Structures investigated include etched and cleaved facets as well as doped and undoped quantum wells. A combination of atmospheric and low-pressure metal organic chemical vapor deposition using a modified two-flow horizontal reactor was employed. Threshold current densities as low as 12.6 kA/cm 2 were observed for 10 2 1200 m lasers with uncoated reactive ion etched facets on c-plane sapphire. Cleaved facet lasers were also demonstrated with similar performance on a-plane sapphire. Laser diodes tested under pulsed conditions operated up to 6 h at RT. Lasing was achieved up to 95 C and up to a 150-ns pulselength (RT). Threshold current increased with temperature with a characteristic temperature T 0 of 114 K.

Blue-emitting nitride laser diodes have been fabricated on a-plane sapphire (1120). The active region is composed of 10 In.18Ga.82N quantum wells, which were grown by MOCVD at atmospheric and low pressure in a modified two-flow Thomas-Swan Ltd. horizontal reactor. The chemical precursors used were trimethylgallium (TMGa), trimethylindium (TMIn), trimethylaluminum (TMAI), ammonia, and disilane. The n- and p-contacts were formed by depositing Ti/Al/Ni/Au and Ni/Au/Ni/Au, respectively. Diode wafers were thinned to less than 50 μm before they were cleaved along the sapphire r-plane (1120).Lasers show TE polarization, spectral line narrowing, and far field interference patterns above the lasing threshold. The laser emission spectra peak at 410–420 nm. Under pulsed operation at room temperature, the lowest observed threshold current density was 15 kA/cm2 with threshold voltages ranging from 50–90 V. Differential efficiencies are as high as 7% with maximum output powers greater than 50 mW. Near and far field mode patterns are presented. Structures are gain-guided devices with each device occupying a mesa with a width of 125 μm. Device widths range from 3 to 20 μm, with lengths of 500 to 1200 μm.