Lasers and laser systems are a mature technology, yet there is a long road ahead for innovation and enthusiasm. We review some of the 40 years of R&D and manufacturing of lasers at ELOP-Elbit Systems. Bulk solid state lasers, for designators and range finders, as well as fiber lasers, for directed IR countermeasures and laser radar applications are described. These two technologies provide and will continue to offer a vast number of products for security and defense applications. Current and future generations of laser products will have higher average power together with improved beam quality, better efficiencies, and superior robustness all in a more compact package.
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.
Ultrashort laser pulses can be used to create high precision incision in transparent and translucent tissue with minimal damage to adjacent tissue. These performance characteristics meet important surgical requirements in ophthalmology, where femtosecond laser flap creation is becoming a widely used refractive surgery procedure. We summarize clinical findings with femtosecond laser flaps as well as early experiments with other corneal surgical procedures such as corneal transplants. We also review laser-tissue interaction studies in the human sclera and their consequences for the treatment of glaucoma.
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.
Approximately five million people worldwide are blind due to complications from glaucoma. Current surgical techniques often fail due to infection and scarring. Both failure routes are associated with damaging surface tissues. Femtosecond lasers allow a method to create a highly precise incision beneath the surface of the tissue without damaging any of the overlying layers. However, subsurface surgery can only be performed where the beam can be focused tightly enough to cause optical breakdown. Under normal conditions, subsurface surgery is not possible since sclera is highly scattering. Using two independent methods, we show completely subsurface surgery in human sclera using a femtosecond laser. The first method is to make the sclera transparent by injecting a dehydrating agent. The second method is to choose a wavelength that is highly focusable in the sclera. Both methods may be applied in other tissues, such as skin. We show highly precise incisions in in vitro tissues. Subsurface femtosecond photodisruption may be useful for in vivo surgical technique to perform a completely subsurface surgery.
The eye is potentially an ideal target for high precision surgical procedures utilizing ultrafast lasers. We present progress on corneal applications now being tested in humans and proof of concept ex vivo demonstrations of new applications in the sclera and lens. Two corneal refractive procedures were tested in partially sighted human eyes: creation of corneal flaps prior to excimer ablation (Femto- LASIK) and creation of corneal channels and entry cuts for placement of intracorneal ring segments (Femto-ICRS). For both procedures, results were comparable to standard treatments, with the potential for improved safety, accuracy and reproducibility. For scleral applications, we evaluated the potential of femtosecond laser glaucoma surgery by demonstrating resections in ex vivo human sclera using dehydrating agents to induce tissue transparency. For lens applications, we demonstrate in an ex vivo model the use of photodisruptively-nucleated ultrasonic cavitation for local and non-invasive tissue interaction.
Subsurface photodisruption is shown to be an effective tool for cutting beneath the surface in human sclera. Using a dehydrating agent to reduce scattering by index matching, photodistruption is possible anywhere in the volume of the sclera. We examine incision in human sclera in vitro using scanning electron microscopy. We found a disorganized material filling the incision and penetrating into the adjacent tissue.
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.
Transcleral photodisruption may provide a noninvasive method for creating partial thickness scleral channels to reduce elevated intraocular pressure associated with glaucoma. We achieved subsurface photodisruption in vitro without damaging overlying tissues with three techniques: (1) use of long laser wavelengths, (2) application of pressure, and (3) application of a dehydrating agent. Using 1 and 3, we were able to photodisrupt the internal surface of a full thickness block of sclera by focusing through the tissue.
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.
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.
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.
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.