We have demonstrated the feasibility of cooling high power solid-state lasers with diamond windows, whose thermal conductivity is about two orders of magnitude higher than sapphire's, the material conventionally used for this purpose. Since pumping and cooling were along the same axis, a Cartesian thermal gradient was achieved, while the zigzag scheme was used to minimize thermal lensing. An output power of 200Watt was achieved from a single Nd:YVO4 slab in a zigzag configuration when pumped with 600Watt diodes at 808nm. The maximum output power previously reported in the literature with Nd:YVO4 using conventional cooling schemes is only about 100W. A 2.3x4x24mm3 slab was pumped from its broad side (4x24 mm2) through a 0.3mm thick optical diamond window placed in close contact with the lasing crystal. The diamond window, held in a water-cooled copper housing acted as a heat conductor. The other broad side of the crystal was cooled directly by its water-cooled copper housing. The output of a two-head configuration was 295Watt. By using a RTP Q-switch, 124Watt average power was obtained at 15kHz with a pulse width of 17nsec, pumping at 650Watt.
An additional larger head was developed to pump a Nd:YAG slab. The concept of the pumping and cooling is identical to the Nd:YVO4 laser head. An output power of 1000Watt was achieved from a single Nd:YAG slab when pumped with 2500Watt diodes at 808nm. The slab dimensions are 3×12×90mm3.
An overview of the ongoing research taking place in our laboratory comparing direct and traditional pumping is given. It includes both Nd:YAG and Nd:YVO4 pumping with either Ti:Sapphire or diode lasers as the pumping source. Latest results addressing basic quantities connected with the pump-lase cycle in Nd:YAG lasers will be presented in detail. By comparing heat generation and laser performance of Nd:YAG oscillators pumped via two channels - direct pumping to the upper lasing level at 885nm and band pumping around 808nm, it was found that the heat generated during lasing is 27% lower with direct pumping as compared to traditional band pumping. Moreover, the experimental results suggest that the coupling efficiency between the pump band and the upper lasing level is unity, and about 8% of the upper lasing level population decays via non-radiative channels.
We have demonstrated the feasibility of cooling high power solid-stae lasers with diamond windows, whose thermal conductivity is about two orders of magnitude higher than sapphire's. An output power of 200Watt was achieved froma single Nd:YVO4 slab in a zigzag configuration when pumped with 600Watt diodes at 808nm. The maximum output power reported in the literature with conventional cooling schemes is about 50W. A 2.3x4x24mm3 slab was pumped from its broad side (4x24 mm2) through a 0.3mm thick optical diamond window placed in close contact with the lasing crystal. The diamond window, held in a water-cooled copper housing acted as a heat conductor. The other broad side of the crystal was cooled directly by its water-cooled copper housing. Since pumping and cooling were along the same axis, a Cartesian thermal gradient was achieved, while the zigzag scheme was used to minimize thermal lensing. By using a BBO Q-switch, 70Watt average power was obtained at 20kHz with a pulse width of 19msec and with a beam quality of 3 and 12 times diffraction limit in the zigzag and transverse directions respectively. The output of a two-head configuration was 295Watt.
Heat generation and laser performance were studied in Nd:YAG oscillators pumped with a Ti:Sapphire laser in two regimes: band pumping at 802nm and direct pumping at 885nm. Slope efficiencies of 52% and 57%, when pumped at 802nm and 885nm, were obtained, respectively. Heat per unit laser output was found to be 27% lower when pumped at 885nm (direct pumping regime) as compared to traditional band pumping around 808nm.
We show a compact multi-pass amplifier, based on a single dual-rod laser-head whihc produces ultra-high gain. A double-pass produced a maximum small signal gain of 4x108. Another pass was permitted by including a specially designed Brillouin phase conjugate mirror (PCM). This enabled a total gain of 7.7x1010, which raised an input signal of 10pJ to 770mJ output signal. To the best of our knowledge this is the highest gain reported to date from any type of laser amplifier scheme. The amplification system is fairly simple in that it consists of only one dual-rod laser head and hence only a single power supply. We show that this system can be utilized for producing high-energy long temporally-smooth narrow linewidth pulses, as well as high power controllable, temporally-modulated pulses.
Utilizing a pulsed beam of a Nd:YAG laser, hole-burning through the opaque cloud of products formed following the detonation of lead azide is demonstrated. The characteristics of the hole and of the expanding cloud are monitored in real time by a HeNe beam and by high- speed framing photography. The hole is carried with the cloud and propagates at a constant velocity of 0.5 - 2.8 km/s, depending on the time and location of burning. The hole-burning is a result of eliminating solid particles from the cloud. The reduction in the number and size of the particles is monitored by scanning electron microscopy of the deposits formed on a substrate following the detonation. The application of a laser to burn a hole in the detonation products from a solid explosive is demonstrated for the first time. This technique may serve as a method for flow visualization in an aerosol medium.
Previous studies in our laboratory have shown that preferential excitation of high lying electronic states of the lead atom is obtained following the detonation of lead azide. However, measurements have shown that the detonation products form an optically opaque medium. In order to overcome this problem, the detonation was conducted via a supersonic nozzle. As a result a transparent medium was formed near the nozzle exit plane. Strong emission from lead atoms was achieved in this medium. Time- and wavelength resolved measurements have shown that the emission intensity of the 3P1° ? 1 D2 transition of the lead atom is significantly enhanced as compared to that from 3P1° to lower lying states. The behavior of the emission is explained in terms of kinetic and spectroscopic (self-trapping) mechanisms. The implication of our results to obtaining laser oscillation following detonation via supersonic nozzles is discussed.
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