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.
Many attempts were made in the past to convert Solar light to Laser light. To date, only two systems were demonstrated successfully: Photo-Dissociation Lasers and Solid State Solar lasers. The absorption spectrum of many dimmer molecules posses a broad structural spectrum overlapping with the solar spectrum and can be good candidates for direct solar pumping. In the gas phase, the emission spectrum of the active medium offers tunability and high beam quality without significant thermal lensing or thermal induced birefringence. Optical characterization and initial pumping experiments of a few selected systems will be discussed.
Solar light is considered as an efficient source for direct optical excitation of solid state lasers. The high efficiency is achieved through the use of different solar spectral bands to pump simultaneously several lasers. In this way it is possible to convert solar energy into laser light at an efficiency of approximately 30% (this value is calculated relative to the solar spectrum inside the atmosphere, after the short UV and far IR are filtered out). Since solar radiation on the ground is unstable, the thermal lensing and other beam quality parameters are not constant and cannot be compensated by standard methods. In the past, most efforts in the development of solar pumped lasers were devoted to the achievement of maximum power and high efficiency while the beam quality was neglected. However, beam quality is important for power transmission, satellite communication, frequency doubling and other applications of solar pumped lasers. A new approach to improve the beam quality of solar pumped solid state lasers using a phase conjugate mirror will be discussed.
The wireless international communication these days faces a practical bandwidth limitation since the frequency band offered by satellites is almost exhausted. In addition, the energy source of a satellite is limited, hence, broadening the frequency domain in a wireless system increases the cost of operation. Free-space optical communication, using direct sun to laser conversion, can contribute to overcome these problems. A lab simulation for outer space solar laser communication was performed. A combination of imaging and non-imaging concentrators for pumping solar laser (oscillator and amplifier) were built and analyzed. An approximated 3D-CPC was designed, assembled and tested. The laser crystal characteristics were measured under the system's pumping conditions. An oscillator-amplifier system was designed built and analyzed. Direct and indirect gain measurements were done. Gain up to 1.4 was measured at a low sun flux of 630 w/m<SUP>2</SUP>. Communication experiments at a boud rate of 1.5 MHz were conducted using intensity modulation outside the cavity.
A lab simulation which demonstrates the power beaming concept, based on solar pumped laser and photovoltaic cell, was performed. The simulation included a parabolic dish, a 3D CPC, a 2D CPC as a laser head for transmission and a photovoltaic cell for converting the laser light into electricity. A waveguide was used in order to obtain a uniform illumination upon the photovoltaic cell. A Nd:YAG laser rod was solar pumped using imaging and nonimaging systems producing 52 Watt laser at sun flux of 830 Watt/m<SUP>2</SUP>. In successive experiments the solar cell was exposed to a laser light using Nd:YAG and Alexandrite lasers. The efficiencies achieved were 33% laser to electricity efficiency for the Nd:YAG laser and approximately 40% for the Alexandrite.
Q-switched, solar-pumped, high power Nd:YAG lasers are attractive for a variety of applications requiring high instantaneous peak power density. The Q-switching can be obtained by an acousto-optic, electro-optic or passive device. Passive Q-switching seems an excellent choice for space as well as for other applications since it neither requires an external driver nor an electrical power supply. In recent years Cr<SUP>+4</SUP>:YAG single crystals were extensively used as passive Q-switches for flashlamp-pumped high power Nd:YAG lasers, demonstrating their superior thermal superior thermal characteristics and durability. In this work we report the first operation of passive Q- switched, solar-pumped, high power Nd:YAG lasers. The concentrated solar energy for he optical pumping of the laser was obtained by a 3-stage combination of imaging and non-imaging optics. It included: i) Weizmann Institute solar tower heliostats, ii) 3D compound parabolic concentrator, and iii) 2D compound parabolic concentrator in which the laser rod was placed. 72 mm long laser rods with either 3 mm or 4 mm diameter were used. The passive Q-switch was made from a Cr$=+4):YAG single crystal having a low- intensity transmission of 72 percent at 1.06 (mu) . Its rear surface was coated by a high reflectivity coating, serving as the rear mirror of the cavity. Output coupling mirrors with various reflectivities were used. The passive Q-switch demonstrated excellent durability and reliability during all the experiments. Repetition rates of 6-39 kHz were measured, showing higher repetition rates at higher laser power levels. The pulses demonstrated shorter full width at half maximum (FWHM) time for higher laser power elves, and the FWHM time range was 190-310 nsec. The maximal measured average power was 14 W. Thermal lensing was measured as a function of the absorbed solar power in the laser rod. It is estimated that laser peak power densities of approximately 100 kW/cm<SUP>2</SUP> were achieved in the experiments. It is believed that near-future modifications may improve this value appreciably.
High power lasers operating at high repetition rates at the kilohertz regime are attractive for a variety of applications. Such high repetition rates can be achieved by Q-switching a cw laser using either an acousto-optic, an electro-optic or a passive Q-switch. Since passive Q-switching needs no external electric circuit, it may be valuable for solar pumped lasers to be used at space. In recent years, Cr<SUP>4+</SUP>:YAG has been extensively used for passive Q-switching of flashlamp pumped Nd:YAG lasers. For high average power lasers, the excellent thermal characteristics of Cr<SUP>4+</SUP>:YAG give it an edge over other saturable absorbers. In the present paper we report on the first passive Q-switching of solar pumped high power Nd:YAG laser. This solar pumped Nd:YAG laser, which employed 3 and 4 mm diameter Nd:YAG rods, emitted up to 50 watts in the cw mode. The laser rod was side-pumped by solar irradiation using a three-stage concentrating system. The Cr<SUP>4+</SUP>:YAG device rear surface was coated by high reflection dielectric coating, serving as cavity rear mirror, while the output mirror had a reflectivity of 90%. An average output power of 9 watts was obtained from the passive Q-switched solar pumped laser at 15 - 40 kHz, twice previous results for a passive Q- switched Nd:YAG laser, results which have been obtained under continuous flashlamp pumping.