Zachary S. Sacks

Precision laser metallization

A process for providing precision deposits (3) of metal films unto a working substrate (5) by transmitting an ultrafast laser pulse thorough a transparent target substrate (6) whose lower surface supports a metal film (7). Rapid laser heating produces pressure that propels vaporized metal unto the working substrate whereupon the metal vapor rapidly resolidifies on a dimension substantially equal to the ultrafast lasers focal spot size.

High precision subsurface photodisruption in human sclera

BACKGROUND AND OBJECTIVES Femtosecond pulses can generate high precision subsurface photodisruption in transparent tissues, such as the cornea. We used femtosecond laser technology to demonstrate early proof of concept for high precision subsurface photodisruption in the translucent sclera. This technique may ultimately enable novel surgical procedures for the treatment of glaucoma and/or presbyopia. STUDY DESIGN/METHODS AND MATERIALS: Microjoule femtosecond pulses from two different sources, 1060 and 775 nm, were used to make subsurface incisions in human sclera in vitro. Scleral tissue was dehydrated to improve translucency at these wavelengths. The beam was focused to a 1.5 (775 nm) or 5 microm spot size (1060 nm) and scanned below the tissue surface at various depths to produce four incision patterns. RESULTS Photodisruption on the backsurface of the sclera was achieved without damage to overlying tissue. Several types of intrascleral incisions were made, including transcleral channels and grooves for scleral implants. CONCLUSIONS High precision, subsurface scleral photodisruption can be achieved in vitro for a variety of intrascleral incisions. Further studies are required to determine if this technique is applicable in vivo for actual surgical applications.

Subsurface Photodisruption in Human Sclera: Wavelength Dependence

BACKGROUND AND OBJECTIVE Approximately 105 million people worldwide have glaucoma, and approximately 5 million are blind from its complications. Current surgical techniques often fail because of scarring of the conjunctival tissue, Tenons tissue, or both. Femtosecond lasers can create highly precise incisions beneath the surface of a tissue, as previously demonstrated in the transparent cornea. Because the sclera is a highly scattering subsurface, photodisruption has not been previously possible. MATERIALS AND METHODS To overcome scattering, a laser operating at 1,700 nm was used to make subsurface cuts in human sclera in vitro via photodisruption. RESULTS Sub-10-microm width incisions were created beneath the surface without collateral tissue effects, something not possible with shorter wavelengths used to date in corneal applications with the femtosecond laser. CONCLUSION Completely subsurface photodisruptions can be accomplished in human sclera in vitro. In vivo studies are required to evaluate the potential use of this technology for scleral applications.

Femtosecond laser corneal refractive surgery

We evaluated the efficacy, safety, and stability of femtosecond laser intrastromal refractive procedures in ex vivo and in vivo models. When compared with longer pulsewidth nanosecond or picosecond laser pulses, femtosecond laser-tissue interactions are characterized by significantly smaller and more deterministic photodisruptive energy thresholds, as well as reduced shock waves and smaller cavitation bubbles. We utilized a highly reliable, all-solid-state femtosecond laser system for all studies to demonstrate clinical practicality. Contiguous tissue effects were achieved by scanning a 5 μm focused laser spot below the corneal surface at pulse energies of approximately 2 - 4 microjoules. A variety of scanning patterns was used to perform three prototype procedures in animal eyes; corneal flap cutting, keratomileusis, and intrastromal vision correction. Superior dissection and surface quality results were obtained for lamellar procedures (corneal flap cutting and keratomileusis). Preliminary in vivo evaluation of intrastromal vision correction in a rabbit model revealed consistent and stable pachymetry changes, without significant inflammation or loss of corneal transparency. We conclude that femtosecond laser technology may be able to perform a variety of corneal refractive procedures with high precision, offering advantages over current mechanical and laser devices and techniques.

Ophthalmic applications of femtosecond lasers

We investigated three potential femtosecond laser ophthalmic procedures: intrastromal refractive surgery, transcleral photodisruptive glaucoma surgery and photodisruptive ultrasonic lens surgery. A highly reliable, all-solid-state system was used to investigate tissue effects and demonstrate clinical practicality. Compared with longer duration pulses, femtosecond laser-tissue interactions are characterized by smaller and more deterministic photodisruptive energy thresholds, smaller shock wave and cavitation bubble sizes. Scanning a 5 (mu) spot below the target tissue surface produced contiguous tissue effects. Various scanning patterns were used to evaluate the efficacy, safety, and stability of three intrastromal refractive procedures in animal eyes: corneal flap cutting, keratomileusis, and intrastromal vision correction (IVC). Superior dissection and surface quality results were obtained for the lamellar procedures. IVC in rabbits revealed consistent, stable pachymetric changes, without significant inflammation or corneal transparency degradation. Transcleral photodisruption was evaluated as a noninvasive method for creating partial thickness scleral channels to reduce elevated intraocular pressure associated with glaucoma. Photodisruption at the internal scleral surface was demonstrated by focusing through tissue in vitro without collateral damage. Femtosecond photodisruptions nucleated ultrasonically driven cavitation to demonstrate non-invasive destruction of in vitro lens tissue. We conclude that femtosecond lasers may enable practical novel ophthalmic procedures, offering advantages over current techniques.

Laser spot size as a function of tissue depth and laser wavelength in human sclera

We determined the wavelength dependence of the minimum spot size of a laser beam focused through human sclera to evaluate the potential for transcleral glaucoma surgical techniques using ultrashort-pulsed lasers. The spectrum of the forward scattered light was measured by collimating the incident and transmitted beam in a spectrophotometer. This spectrum shows that sclera is highly scattering until 1100 nm, after which, the transmission spectrum is similar to water. To measure the minimal spot size, a laser beam was focused on the back surface of sclera of differing thickness. The minimum spot at 800 nm, 1060 nm, 1301 nm, and 1557 nm was imaged. At 800 nm, the spot size was invariant upon focal lens position, being a thousand fold larger than the incident beam spot size. As the wavelength increased, the area of the spot decreased, so that at 1557 nm, the minimal spot size was on the order of the incident beam spot size.

Long wavelength operation of double-clad Tm:silica fiber lasers

Lasers operating at wavelengths that pass through the atmosphere are required for many applications, including lidar/ladar, spectroscopy, and pollution detection. One window of particular interest is between 2050 and 2300 nm. A Tm:silica fiber laser may be a candidate for operating in this window, but reported solutions using double clad fibers only achieved wavelengths up to 2090nm even though the emission spectrum of the lasing band extends beyond 2200nm. By carefully selecting the dopant concentration, mirror reflectivities, and fiber length the operating wavelength may be adjusted. A laser based on a double clad Tm:silica fiber coupled to a bulk grating for wavelength selection was constructed. By changing the output coupler reflectivity the maximum obtainable wavelength shifted from 2040nm to 2140nm, and another mirror resulted in 2188nm lasing operation.

Transscleral photodisruption for the treatment of glaucoma

To evaluate transscleral glaucoma surgery techniques using ultrashort pulsed lasers, we attempted to produce photodisruption on the inner surface of the sclera without damaging the overlying tissue. We identified two methods, using pulses centered at 1700 nm and a transparency inducing drug, to produce the spatial and temporal confinement of the pulse necessary to produce photodisruption in the highly scattering sclera. When fully developed these concepts may help address the longstanding limitations of current glaucoma surgical techniques.

Femtosecond subsurface photodisruption in scattering human tissues using long infrared wavelengths

Approximately 5 million people worldwide are blind due to complications from glaucoma, and an estimated 105 million have the disease. Current surgical techniques often fail due to scarring that is associated with disruption of the ocular surface tissues using conventional surgical methods. Demonstrated in the transparent cornea, femtosecond lasers can create a highly precise incision beneath the surface of a tissue. Since sclera is highly scattering with one micron light, the same wavelength used in cornea cannot be focused to the small spot necessary for photodisruption far beneath the surface of sclera. We now demonstrate completely subsurface incisions in human sclera by selecting a laser wavelength that is focusable beneath the surface, namely 1700 nm. Similar techniques may be used in other translucent tissues such as skin. Subsurface femtosecond photodisruption may be a useful for in vivo surgical technique to perform a completely subsurface surgery.

Spatially resolved transmission of highly focused beams through the cornea and sclera between 1400 and 1800 nm

We investigated the spatial confinement of laser beams focused through human cornea and sclera using long near infrared wavelengths. Using a 0.4 numerical aperture lens, we measured the spatial transmission of the smallest emergent beam on the back surface of the tissue. We found that standard axial transmission measurements over estimate the amount of unscattered light for the sclera and that 1600 nm to 1700 nm had the maximum unscattered transmission through cornea and sclera. The light confinement may be useful in producing localized subsurface linear and nonlinear optical processes.