Julio C Ramirez-San-Juan - Academia.edu (original) (raw)

Papers by Julio C Ramirez-San-Juan

The synthesis of diffraction-free fields with different profiles is described. The synthesis is d... more The synthesis of diffraction-free fields with different profiles is described. The synthesis is done by illuminating a screen containing a circular slit with a cosine beam. The treatment is equivalent to the modulation of the slit transfer characteristics and makes possible a tunable interference interaction of Bessel beams with noncommon axes. These results are generalized, and it is shown that coherent diffraction-free fields with arbitrary profiles can be expressed as the superposition of shifted zero-order Bessel beams and temporary parametric representations of the shifted functions. Diffraction-free fields with partially coherent features can be obtained. Experimental results are shown for each case.

Optical Trapping and Optical Micromanipulation V, 2008

The use of spatial light modulators to generate arbitrary optical field distributions has been ex... more The use of spatial light modulators to generate arbitrary optical field distributions has been extensively used to trap and manipulate dynamically a large number of particles. Here we show that by using phase computer generated holograms displayed on a spatial light modulator (SLM) sorting of microparticles can be achieved at relatively low power. The algorithm used for the generation of the PCGH is based on iterative Fourier transform algorithm which generate a spots array in the Fourier plane, then controlling some parameters as: the spot separation, the direction and velocity of the pattern displacement, optical sorting of micron-sized particles can be achieved.

Cryogen spray cooling (CSC) is a technique employed to reduce the risk of epidermal damage during... more Cryogen spray cooling (CSC) is a technique employed to reduce the risk of epidermal damage during dermatologic laser surgery. However, while CSC protects the epidermis from non-specific thermal damage, it might reduce the effective fluence reaching the target chromophore due to scattering of light by the spray droplets and subsequent water condensation/freezing on the skin surface. The objective of this work was to study the effect of ambient humidity (ω) on light transmittance during CSC. An integrating sphere was employed to measure the dynamics of light transmittance through a deformable agar phantom during CSC. The study included two representative CSC spurt patterns studied using four ω: 57, 40, 20 and 12%. Results show that during CSC, as ω increased, light transmittance decreased. For the highest humidity level (57%) studied, light transmittance reached a minimum of 55% approximately 30 ms after spurt termination. In a controlled environment with ω = 12%, light transmittance reached a minimum of 87% approximately 30 ms after spurt termination. The reduced light transmittance immediately after spurt termination was most likely because of scattering of light caused by condensation of water vapour due to aggressive cooling of ambient air in the wake of the cryogen spurt.

Archives of Facial Plastic Surgery, 2005

P ort-wine stain (PWS) birthmarks are congenital, low-flow vascular malformations of the skin. La... more P ort-wine stain (PWS) birthmarks are congenital, low-flow vascular malformations of the skin. Lasers are the modality of choice for the treatment of PWS birthmarks, and for most patients the pulsed-dye laser in conjunction with epidermal cooling offers the greatest efficacy and safety. Other light devices, including the 532-nm frequency-doubled Nd:YAG laser, intense pulsed light, 1064-nm Nd:YAG laser, and combined 1064/532-nm system, may be useful during a treatment course for resistant PWS. Laser treatment results in blanching of most lesions, although complete resolution may not occur and some resistant PWS birthmarks respond minimally, if at all. Factors limiting laser treatment include variable vascular geometry, inadequate damage of some vessels, and lesional posttreatment recurrence as a result of neovascularization. Alternative or adjunct treatment options that address these limitations should be explored, including noninvasive real-time imaging to optimize the selection of treatment settings, photodynamic therapy, and perioperative use of antiangiogenic compounds.

The synthesis of diffraction-free fields with different profiles is described. The synthesis is d... more The synthesis of diffraction-free fields with different profiles is described. The synthesis is done by illuminating a screen containing a circular slit with a cosine beam. The treatment is equivalent to the modulation of the slit transfer characteristics and makes possible a tunable interference interaction of Bessel beams with noncommon axes. These results are generalized, and it is shown that coherent diffraction-free fields with arbitrary profiles can be expressed as the superposition of shifted zero-order Bessel beams and temporary parametric representations of the shifted functions. Diffraction-free fields with partially coherent features can be obtained. Experimental results are shown for each case.

Optical Trapping and Optical Micromanipulation V, 2008

The use of spatial light modulators to generate arbitrary optical field distributions has been ex... more The use of spatial light modulators to generate arbitrary optical field distributions has been extensively used to trap and manipulate dynamically a large number of particles. Here we show that by using phase computer generated holograms displayed on a spatial light modulator (SLM) sorting of microparticles can be achieved at relatively low power. The algorithm used for the generation of the PCGH is based on iterative Fourier transform algorithm which generate a spots array in the Fourier plane, then controlling some parameters as: the spot separation, the direction and velocity of the pattern displacement, optical sorting of micron-sized particles can be achieved.

Cryogen spray cooling (CSC) is a technique employed to reduce the risk of epidermal damage during... more Cryogen spray cooling (CSC) is a technique employed to reduce the risk of epidermal damage during dermatologic laser surgery. However, while CSC protects the epidermis from non-specific thermal damage, it might reduce the effective fluence reaching the target chromophore due to scattering of light by the spray droplets and subsequent water condensation/freezing on the skin surface. The objective of this work was to study the effect of ambient humidity (ω) on light transmittance during CSC. An integrating sphere was employed to measure the dynamics of light transmittance through a deformable agar phantom during CSC. The study included two representative CSC spurt patterns studied using four ω: 57, 40, 20 and 12%. Results show that during CSC, as ω increased, light transmittance decreased. For the highest humidity level (57%) studied, light transmittance reached a minimum of 55% approximately 30 ms after spurt termination. In a controlled environment with ω = 12%, light transmittance reached a minimum of 87% approximately 30 ms after spurt termination. The reduced light transmittance immediately after spurt termination was most likely because of scattering of light caused by condensation of water vapour due to aggressive cooling of ambient air in the wake of the cryogen spurt.

Archives of Facial Plastic Surgery, 2005

P ort-wine stain (PWS) birthmarks are congenital, low-flow vascular malformations of the skin. La... more P ort-wine stain (PWS) birthmarks are congenital, low-flow vascular malformations of the skin. Lasers are the modality of choice for the treatment of PWS birthmarks, and for most patients the pulsed-dye laser in conjunction with epidermal cooling offers the greatest efficacy and safety. Other light devices, including the 532-nm frequency-doubled Nd:YAG laser, intense pulsed light, 1064-nm Nd:YAG laser, and combined 1064/532-nm system, may be useful during a treatment course for resistant PWS. Laser treatment results in blanching of most lesions, although complete resolution may not occur and some resistant PWS birthmarks respond minimally, if at all. Factors limiting laser treatment include variable vascular geometry, inadequate damage of some vessels, and lesional posttreatment recurrence as a result of neovascularization. Alternative or adjunct treatment options that address these limitations should be explored, including noninvasive real-time imaging to optimize the selection of treatment settings, photodynamic therapy, and perioperative use of antiangiogenic compounds.