Recently, interest in diode laser-pumped solid-state lasers has increased due to their advantages over flashlamp-pumped solid-state lasers. A historical overview is presented of semiconductor diode-pumped solid-state lasers beginning with work in the early 1960s and continuing through recent work on wavelength extension of these devices by laser operation on new transitions. Modeling of these devices by rate equations to obtain expressions for threshold, slope efficiency, and figures of merit is also given. >

Diode laser-pumped solid-state lasers

Many solid-state lasers of current interest exhibit reabsorption loss. Previous modeling calculations of laser performance with longitudinal pumping either have neglected reabsorption loss or have been valid only for certain special cases of the ratio of the pump- and laser-beam waists. Rigorous numerical modeling calculations have been carried out to provide a comprehensive understanding of the behavior of longitudinally pumped solid-state lasers, including reabsorption loss and for arbitrary sizes of the pump- and laser-beam waists. In addition, certain aspects of laser behavior that have traditionally not been discussed in papers on laser modeling, such as clamping, saturation, and spatial distribution of the population-inversion density, are investigated to provide a general understanding of laser performance. The results are applied to a particular solid-state laser of current practical interest, the 946-nm Nd:YAG laser.

Modeling of longitudinally pumped solid-state lasers exhibiting reabsorption losses

Laser energy produced by a laser operating in the mid-infrared region (approximately 2 micrometers) is delivered by an optical fiber in a catheter to a surgical site for biological tissue removal and repair. Disclosed laser sources which have an output wavelength in this region include: Holmium-doped Yttrium Aluminum Garnet (Ho:YAG), Holmium-doped Yttrium Lithium Fluoride (Ho:YLF), Erbium-doped YAG, Erbium-doped YLF and Thulium-doped YAG. For tissue removal, the lasers are operated with relatively long pulses at energy levels of approximately 1 joule per pulse. For tissue repair, the lasers are operated in a continuous wave mode at low power. Laser output energy is applied to a silica-based optical fiber which has been specially purified to reduce the hydroxyl-ion concentration to a low level. The catheter may be comprised of a single optical fiber or a plurality of optical fibers arranged to give overlapping output patterns for large area coverage.

Infrared laser catheter system

A model is developed for an end-pumped quasi-three-level laser with population in the lower laser level at equilibrium such as for transitions to the manifolds4I 9/2 in Nd3+,4I 15/2 in Er3+,5I 8 in Ho3+and3H 6 in Tm3+. It is shown that the effect of residual lower laser level population on laser operation can be treated as a saturable loss. Room temperature operation on the4F 3/2 -4I 9/2 transition in Nd:YAG under CW dye laser pumping has been demonstrated with a threshold as low as 11.5 mW incident power and a slope efficiency of 7 percent with 0.3 percent output coupling. Performance is limited by the low output coupling and diffraction loss.

Modeling and CW operation of a quasi-three-level 946 nm Nd: YAG laser

A method of fabricating a semiconductor structure including the steps of providing a silicon substrate (10) having a surface (12), forming on the surface (12) of the silicon substrate (10), by atomic layer deposition (ALD), a seed layer (20;20') characterised by a silicate material and forming, by atomic layer deposition (ALD) one or more layers of a high dielectric constant oxide (40) on the seed layer (20;20').

Method for fabricating a semiconductor structure including a metal oxide interface with silicon

Pump-size effects in Nd:YAG lasers.

The low voltage operation of this electro-optic modulator is realized by a unique system configuration in which the input light beam is first separated into two linearly polarized components of equal intensity, the beams are then focused into two crystals where the beams propagate as pure E waves, the crystals are electrically modulated and the output beams from each crystal are then recombined and recollimated. The low voltage operation is rendered possible by the fact that there is no cancellation between the E and O components as in conventional modulation systems of this type since both beams are transmitted as pure E waves during the modulation process.

Low voltage electro-optic modulator

Broadband electrooptical modulator means for use in optical and electrooptical communication systems and the like, the modulator means including modulator driver and driver amplifier means, broadband matching network means, temperature control means, and means to automatically compensate for variations including electronic variations in the output. The subject modulator means employ optically coupled crystal elements which have their optical Z-axes oriented perpendicularly to each other to cancel natural birefringence and to reduce temperature sensitivity including the temperature sensitivity of the extinction ratio of the crystals.

Broadband electrooptical modulator

A solid state laser rod and a mount through which heat is dissipated from the rod are joined together at a bond comprised of a reflective layer on the surface of the rod, a barrier layer over the reflective layer, and a solder layer between the barrier layer and the mount. The reflective layer may be applied by sputter or other deposition procedures and is highly reflective in the region of the spectrum at which the laser operates, thus insuring optimum efficiency for the rod. The barrier layer may be applied to the reflective layer by the same deposition procedure, and it is impervious to the solder so that the solder does not penetrate it and scavenge the reflective layer. The solder should have a low melting point so as to avoid setting up excessive mechanical stresses in the rod when the solder solidifies. Both the mount and the barrier layer may be covered with a wetting layer prior to soldering to achieve better adhesion of the solder.

Bond and method of making the same

A laser diode suitable for integrated and fiber optic applications requiring single transverse and single longitudinal mode operation. The single transverse mode is provided by making a gallium arsenide double heterostructural laser diode with a narrow stripe width and a relatively long length. The single longitudinal mode operation is provided by cracking the diode transverse to the stripe at one or more locations to form internal etalons in the laser cavity.

Robert R. Rice

Papers

Pump-size effects in Nd:YAG lasers.

Low voltage electro-optic modulator

Broadband electrooptical modulator

Bond and method of making the same

Etalon laser diode