The present invention relates to lasers, and more particularly, to high energy storage, high gain, eyesafe, Er lasers useful for military and commercial applications.
A need has emerged for the development of high gain, high energy Q-switched lasers for military and commercial applications that operate in the eyesafe region (xcexxcx9c greater than 1.5 microns). The military requirement is the augmentation of fire control systems with a system that can identify the target (Target ID). The Target ID function is achieved with an electro-optic sensor that illuminates the target with high energy, short pulse eyesafe radiation (1.5 microns) and generates a real time image with the return radiation using a gated image intensifier or an array of high speed photo to diode.
Commercial applications of high gain eyesafe lasers include the development of free space communication nodes of conventional fiber optic networks. Free space networks which are capable of transmitting and receiving the data of fiber optic communication links can dramatically reduce the capital cost of point to point fiber optic cable installation. Free space communication would be enabled by the development of high gain Er amplifier modules that would amplify the output of existing fiber networks to achieve reliable free space communications. Free space communications must operate in all weather environments requiring the transmission of high power; hence the high gain requirement.
Conventional technology utilizes Yb sensitized Er glass or Er fiber lasers. This technology has found wide military (eyesafe rangefinders) and commercial (fiber communications) application. However, these technologies (Ybxe2x80x94Er glass and fiber lasers) cannot provide the high gain, high energy storage properties needed for generation of moderate to high energy laser radiation for military application or the high gain needed for free space communication applications. The problem with the Ybxe2x80x94Er glass is the requirement of high population densities in the upper level, which densities are needed to achieve gain and high energy. High sensitizer (Yb) concentrations are needed to absorb the pump energy, and transfer it to the upper laser level. The high population densities at the upper laser level generally back transfer, also known as upconversion, to the sensitizer, thus limiting the amount of energy that can be stored. Gain is proportional to stored energy, stored energy to laser output. Ybxe2x80x94Er glass technology cannot provide high energy laser output or high gain.
An alternative technology for military applications is the use of diode pumped Nd lasers driving non-linear devices which shift the one micron laser output to the eyesafe region (xcex greater than 1.5 microns). This technology is capable of high Q-switched eyesafe energies but is very costly to implement. High cost is the result of the short storage lifetime of Nd lasers (200 xcexcs). Typical diode bars emit 100 watts of peak power. The energy stored in the Nd laser is proportional to the product of the diode peak powerxc3x97the storage lifetime of the laser material.
In accordance with the present invention there is provided an eyesafe, Q-switched laser for target identification purposes or an Er gain medium for amplification of Er fiber communication links. The invention comprises a resonant pumped Er laser configured as a Q-switched oscillator or multipass amplifier.
The eyesafe Q-switched laser or multipass amplifier consists of unsensitized Er, having a lifetime of xcx9c10 milliseconds for a 1.5 micron transition. The range of concentrations is approximately between 0.1 and 2.0% of the active ion. The oscillator material can comprise erbium dispersed in a number of crystalline or glass media. The laser system has the following performance values:
Energy/pulse: between approximately 250 and 300 mJ
Wavelength: xcx9c1.5 microns
Pump source: xcx9c30 to 60 W at 1.5 microns for xcx9c10 ms
Gain: gain coefficient xcx9c1 cmxe2x88x921 
It is an object of the present invention to provide a low cost, Q-switched laser for target identification, ranging, and gated viewing.
It is another object of this invention to provide a means of amplifying the output of a fiber communications link.
It is another object of this invention to provide a Resonant Pumped Erbium (RPE) laser, which exhibits a long storage lifetime, thereby minimizing the number of diodes needed to achieve high stored energy and high gain.