Victor H. Hasson

Compact and efficient DPSS laser using diamond-cooled technology

In this paper, we summarize the performance of a diamond cooled diode pumped solid state (DPSS) Nd:YAG laser developed by Textron Systems Corporation (TCS). Over 50% intrinsic extraction efficiency at 50-Watts average power, equivalent to volumetric power extraction of 2000 W/cc, has been experimentally demonstrated. Beam quality (BQ) of less than 1.1 XDL has been measured in an oscillator configuration with the laser operating in TEM00 mode. With a simple passive thermal lens correction, BQ of less than 1.5 XDL was obtained from an oscillator amplifier arrangement at specific pump rates up to 1600 W/cc and 600 W/cc, respectively. By using an intra-cavity acousto-optic modulator, Q-switched laser pulses as short as 6 ns were obtained from the oscillator. This concept is amenable to scaling up to very high power levels. A conceptual design, using our validated database, for a 100-kW class laser is also presented.

Review of design concepts and diagnostics for 100-KW-class repetitively pulsed CO2 lasers

This paper reviews the basic phenomena and technologies associated with design of repetitively pulsed CO2 lasers operating at power levels of ~ 100 kW and pulse repetition rates of ~ 100 Hz and includes some simple diagnostic techniques. Such systems are of potential interest for materials processing investigations and as potential drivers for higher power systems for launching of small payloads to space.

Pulse selection from a mode-locked TE CO2 laser output using a resonant acousto-optic modulator

The pulse separation and associated range ambiguity of a CO2 laser radar using a pulse burst waveform consisting of 1.3 ns mode-locked pulses spaced 40 ns apart was successfully doubled to 80 ns and 12 m respectively by suppressing every alternate pulse. This was done by sending the mode-locked laser output beam with 40 ns pulse spacing through a resonant Raman-Nath acousto-optic modulator driven at 18.75 MHz which is 1.5 times the drive frequency used to intracavity mode-lock the CO2 laser transmitted. The spatial filtering of the diffracted pulses results in the suppression of the alternate pulses to better than 15 dB. The throughputs for the unsuppressed pulses were greater than 95%. The laser radar capability in detecting large targets, Photonics West PW 48 1998-01-24|1998-01-30 Optoelectronics and High-Power Lasers & Applications PW98 263761 San Jose, CA, USA Gas and Chemical Lasers and Intense Beam Applications 3268 CO and CO2 Lasers and Applications 1

Use of laser radar for small space object experiments

This report briefly reviews the development, capabilities, and current status of pulsed high-power coherent CO2 laser radar systems at the Maui Space Surveillance System (MSSS), HI, for acquisition, tracking, and sizing of orbiting objects. There are two HICLASS systems, one integrated to the 0.6 m Laser Beam Director and one just integrated Summer 2000 to the 3.7 m Advanced E-O System (AEOS). This new system takes full advantage of the large AEOS aperture to substantially improve the ladar range and sensitivity. These improvements make the AEOS HICLASS system potentially suitable for tracking and characterization experiments of small < 30 cm objects in low-earth-orbits.

Eye-safe lidar receiver using Er3+: fiber optical preamplifier

We have demonstrated a 15 dB lidar receiver detection sensitivity improvement by employing an Er3+-doped fiber preamplifier as the input to an InGaAs P-I-N photodiode. This eye-safe, 1550 nm detection system can significantly improve lidar system performance. It is shown that it is comparatively easier at 1550 nm than at 1064 nm to achieve a higher detection sensitivity for a lidar system using a fiber preamplifier in comparison with that using an avalanche photodiode (APD). The reason is that the Er:fiber preamplifier performs better than a Nd:fiber preamplifier, while the InGaAs APD is less sensitive in comparison with a Si APD. In a lidar receiver using a fiber preamplifier, the beam coupling efficiency from free-space mode to a single- mode fiber is the critical parameter. For moderate target velocities, an automatic front-end alignment system using piezoelectric transducers can be effected to yield a good coupling efficiency. The design and preliminary test results of such a lidar receiver are discussed in terms of optimized optical filter bandwidth, optical preamplifier gain and noise figure, and input saturation level.

Overview of the field ladar demonstration program developing high-resolution imaging and remote sensing

The paper reviews the basic capabilities and utility of the FLD laser radar system and highlights key features which lead to a combined LADAR/LIDAR capability.

Effect of the vibration‐translation transfer rate on laser‐induced frequency chirp in a long‐pulse CO2 laser

A frequency sweeping (chirping) mechanism governed by the lasing gas pressure and composition has been observed in a long‐pulse TE CO2 laser for the first time. The mechanism was detected in heterodyned data obtained from photomixing the pulsed laser output with a cw local oscillator. A theory has been developed which links this chirp‐governing mechanism to the vibration‐translation (V‐T) transfer rate from the lower laser level to the ground state. This new theory extends the existing theories on chirp in pulsed CO2 lasers into the long‐pulse regime.

A compact Nd:YAG DPSSL using diamond-cooled technology

In our diamond-cooled approach, thin disks of laser gain material, e.g., Nd:YAG, are alternated between thin disks of single crystal synthetic diamond whose heat conductivity is over 2000 W/m-°K. The gain medium is face-pumped (along the optical axis) by the output of laser diode arrays. This optical configuration produces heat transfer from Nd:YAG to the diamond, in the direction of the optical axis, and then heat is rapidly conducted radially outward through the diamond to the cooling fluid circulating at the circumference of the diamond/YAG assembly. This geometry effectively removes the heat from the gain material in a manner that permits the attainment of high power output with excellent beam quality.

Passive ranging through the Earth's atmosphere

Many luminous sources provide continuous or quasi-continuous radiation at near IR and longer wavelengths. The radiation continuum serves as a source of background photons, which can be used for discrete line-of-site absorption measurements by-known atmospheric constituents. The intensity ratio is uniquely determined by the absorption coefficient and range, is independent of broadband attenuations and scattering. The absorption coefficients are known and/or can be accurately calculated for a wide range of practical viewing conditions (i.e., sensor height, viewing angle, etc.). Hence, the intensity ratio and/or integrated intensity ratio can be used to uniquely derive the range of the radiating source. Fabry-Perot interferometers can provide the high throughputs and resolving powers required in compact packages. The measurements and analyses show that ranging accuracies representing down to 1 - 2% of the total range should be achievable at stand-off ranges of upto hundreds of kilometers depending on the size of the collection optics, brightness of the source and available observation times. The paper will provide an overview of the patented Textron concepts, trade-offs associated with instrument resolving powers and hardware implementation issues.

Acquisition, tracking, and sizing of small space objects

High-powered, pulsed CO2 coherent ladar systems and their potential application to space debris tracking and characterization.