Compact laser radar and three-dimensional camera

A novel three-dimensional (3D) camera is capable of providing high-precision 3D images in real time. The camera uses a diode laser to illuminate the scene, a shuttered solid-state charge-coupled device (CCD) sensor, and a simple phase detection technique based on the sensor shutter. The amplitude of the reflected signal carries the luminance information, while the phase of the signal carries range information. The system output is coded as a video signal. This camera offers significant advantages over existing technology. The precision in range is dependent only on phase shift and laser power and theoretically is far superior to existing time-of-flight laser radar systems. Other advantages are reduced size and simplicity and compact and inexpensive construction. We built a prototype that produced high-resolution images in range the (z) and x-y.     

Three-dimensional imaging laser radar with a photon-counting avalanche photodiode array and microchip laser

We have developed a threedimensional imaging laser radar featuring 3-cm range resolution and single-photon sensitivity. This prototype direct-detection laser radar employs compact, all-solid-state technology for the laser and detector array. The source is a Nd:YAG microchip laser that is diode pumped, passively Q-switched, and frequency doubled. The detector is a gated, passively quenched, two-dimensional array of silicon avalanche photodiodes operating in Geigermode. After describing the system in detail, we present a three-dimensional image, derive performance characteristics, and discuss our plans for future imaging three-dimensional laser radars.     

Gated viewing and high-accuracy three-dimensional laser radar

We have developed a fast and high-accuracy three-dimensional (3-D) imaging laser radar that can achieve better than 1-mm range accuracy for half a million pixels in less than 1 s. Our technique is based on range-gating segmentation. We combine the advantages of gated viewing with our new fast technique of 3-D imaging. The system uses a picosecond Q-switched Nd:Yag laser at 532 nm with a 32-kHz pulse repetition frequency (PRF), which triggers an ultrafast camera with a highly sensitive CCD with 582 x 752 pixels. The high range accuracy is achieved with narrow laser pulse widths of approximately 200 ps, a high PRF of 32 kHz, and a high-speed camera with gate times down to 200 ps and delay steps down to 100 ps. The electronics and the software also allow for gated viewing with automatic gain control versus range, whereby foreground backscatter can be suppressed. We describe our technique for the rapid production of high-accuracy 3-D images, derive performance characteristics, and outline future improvements.     

Deep-etched high-density fused-silica transmission gratings with high efficiency at a wavelength of 1550 nm

We describe the design, fabrication, and excellent performance of an optimized deep-etched high-density fused-silica transmission grating for use in dense wavelength division multiplexing (DWDM) systems. The fabricated optimized transmission grating exhibits an efficiency of 87.1% at a wavelength of 1550 nm. Inductively coupled plasma-etching technology was used to fabricate the grating. The deep-etched high-density fused-silica transmission grating is suitable for use in a DWDM system because of its high efficiency, low polarization-dependent loss, parallel demultiplexing, and stable optical performance. The fabricated deep-etched high-density fused-silica transmission gratings should play an important role in DWDM systems.     

External-cavity wavelength tunable laser with an electro-optic deflector

A near-IR tunable external-cavity laser that uses an electro-optic deflector and a reflection grating as a tunable filter is demonstrated. The deflector is an electronically reconfigurable nonpixelated nematic liquid-crystal device. By controlling the voltage applied to the electro-optic deflector, a tuning range of 12 nm and a side-mode suppression higher than 30 dB are obtained.     

Optical breakdown on a target surface under a simultaneous laser pulse action at the wavelength of 248 and 532 nm

It is found that under, a double-pulse optical breakdown, the energy of the main pulse with a wavelength of 532 nm is diminished by up to two times, provided that the preionization of the target surface is performed by a laser pulse with a wavelength of 248 nm. It is shown that the pulse of a shorter wavelength can act as the managing one to specify the optical-breakdown onset and coordinates.     

Highly birefringent photonic crystal fibers with near-zero dispersion at 1550 nm wavelength

This paper presents highly birefringent photonic crystal fibers with simultaneously near-zero dispersion and low confinement losses. The finite difference time domain method with anisotropic perfectly matched layer boundaries is used as the simulation software. According to simulation, it is shown that photonic crystal fibers with hybrid cladding and artificial defects along one of the orthogonal axes sufficiently results in a very high birefringence of the order 10^?2 which is two orders of magnitude higher than that of the conventional polarization maintaining fibers. Such a fiber also assumes both near-zero dispersion and low confinement losses at the 1550 nm wavelength. Optical fibers with novel properties such as high birefringence, near-zero dispersion, and low confinement losses may have applications in optical sensing applications.     

Coherent laser radar at 3.6 microm

Coherent laser radar systems in the mid-IR wavelength region can have advantages in low-altitude environment because they are less sensitive to scattering, turbulence, and humidity, which can affect shorter- or longer-wavelength system. We describe a coherent laser radar at 3.6 microm based on a single-frequency optical parametric oscillator and demonstrate the system over short ranges outdoors. The system was used to make micro-Doppler measurements from idling trucks that were processed to give surface vibration spectra.     

Performance of normal-incidence molybdenum-yttrium multilayer-coated diffraction grating at a wavelength of 9 nm

The first experimental investigation of a normal-incidence Mo-Y multilayer-coated diffraction grating operating at a 9-nm wavelength is reported. The substrate is a replica of a concave holographic ion-etched blazed grating with 2,400 grooves/mm and a 2-m radius of curvature. The measured peak efficiency in the -3 order is 2.7% at a wavelength of 8.79 nm. To our knowledge, this is the highest normal-incidence grating efficiency ever obtained in this wavelength region.     

Efficient laser operation of an Yb:S-FAP crystal at 985 nm

We have obtained three-level cw laser operation at 985 nm with a Yb-doped S-FAP bulk crystal pumped by a Ti:sapphire laser. An output power of 250 mW for an incident pump power of 1.45 W has been achieved, which is the highest cw output power ever obtained, to our knowledge, at this wavelength with a Yb-doped crystal. The experimental results are in good agreement with the numerical model that we have developed.     

The BIPM laser standards at 633 nm and 532 nm simultaneously linked to the SI second using a femtosecond laser in an optical clock configuration

A femtosecond laser comb was used in an optical clock configuration to measure simultaneously the optical frequency of an iodine-stabilized Nd:YAG laser at 532 nm and an iodine-stabilized He-Ne laser at 633 nm at the International Bureau of Weights and Measures (BIPM). The noise characteristics of the data corresponds well to those of the reference standards and the lasers under study. In a second series of measurements during which the comb was phase-locked to a hydrogen maser, laser standards at 532 nm and at 633 nm were measured. A standard deviation of 6/spl times/10/sup -15/ during 2 h of measurements for the Nd:YAG laser illustrates well the excellent stability of these standards and, at the same time, the capabilities of the comb techniques.     

Mo/B4C/Si multilayer-coated photodiode with polarization sensitivity at an extreme-ultraviolet wavelength of 13.5 nm

A silicon photodiode coated with an interface-engineered Mo/Si multilayer was developed as a polarization sensitive detector. The Mo/B4C/Si multilayer was designed to reflect 13.5-nm extreme-ultraviolet (EUV) radiation at an incident angle of 45 degrees, at which the maximum polarization sensitivity occurs. The sensitivity of this specially coated photodiode and its polarization responses were determined by measurement of the reflectance and transmittance of the multilayer coating with synchrotron radiation. The Mo/B4C/Si multilayer was found to reflect 69.9% of the s-polarized radiation and only 2.4% of the p-polarized radiation, thus transmitting approximately 0.2% s-polarized radiation and 8.4% p-polarized radiation at a 13.5-nm wavelength and a 45 degrees angle of incidence. A polarization ratio, (Tp - Ts)/(Tp + Ts), of 95% was achieved with sufficiently high sensitivity from this photodiode. This result demonstrates the high polarization sensitivity and the usefulness of multilayer-coated photodiodes as novel EUV polarimeters.     

High-power deuterium Raman laser at 632 nm

We demonstrate a continuous-wave deuterium Raman laser that generates more than 160 mW of Stokes output power despite severe thermal effects. This output power represents nearly an order-of-magnitude increase over any previously reported continuous-wave Raman laser and is the first such system to our knowledge that uses deuterium gas as the Raman medium. The high output power is achieved through careful consideration of the electronic feedback design, frequency actuators, and pump-laser intensity noise.     

Photon-counting compressive sensing laser radar for 3D imaging

We experimentally demonstrate a photon-counting, single-pixel, laser radar camera for 3D imaging where transverse spatial resolution is obtained through compressive sensing without scanning. We use this technique to image through partially obscuring objects, such as camouflage netting. Our implementation improves upon pixel-array based designs with a compact, resource-efficient design and highly scalable resolution.     

Characterization of a high-brilliance soft x-ray laser at 13.9 nm by use of an oscillator-amplifier configuration

We have improved a highly coherent x-ray laser at 13.9 nm using an oscillator-amplifier configuration. To improve a high-brilliance x-ray laser, we adopted traveling wave pumping for the amplifier target and rotated the amplifier target 3-4 mrad in the counterclockwise direction. Thereby, a seed x-ray laser can be amplified by medium plasma of the amplifier target with a high gain coefficient. The amplified x-ray laser has the output energy of approximately 1.3 microJ, corresponding to a large photon flux of 6.5 x 10(10) photons/pulse and a high peak brilliance of 5 x 10(26) photons/(s x mm(2) x mrad(2) x 0.01% bandwidth).     

1.86 W cw single-frequency 1319 nm ring laser pumped at 885 nm

A 1.86 W cw single-frequency 1319 nm laser was produced by using an 885 nm-pumped Nd:YAG crystal with a compact four-mirror ring cavity, for the first time to our knowledge. The Nd:YAG produced a slope efficiency of 21% and an optical-to-optical efficiency of 18% with respect to the absorbed diode pump power. A near-diffraction-limited beam with M(2)=1.2 was achieved under the maximum output power.     

Synthetic-aperture imaging laser radar: laboratory demonstration and signal processing

The spatial resolution of a conventional imaging laser radar system is constrained by the diffraction limit of the telescope's aperture. We investigate a technique known as synthetic-aperture imaging laser radar (SAIL), which employs aperture synthesis with coherent laser radar to overcome the diffraction limit and achieve fine-resolution, long-range, two-dimensional imaging with modest aperture diameters. We detail our laboratory-scale SAIL testbed, digital signal-processing techniques, and image results. In particular, we report what we believe to be the first optical synthetic-aperture image of a fixed, diffusely scattering target with a moving aperture. A number of fine-resolution, well-focused SAIL images are shown, including both retroreflecting and diffuse scattering targets, with a comparison of resolution between real-aperture imaging and synthetic-aperture imaging. A general digital signal-processing solution to the laser waveform instability problem is described and demonstrated, involving both new algorithms and hardware elements. These algorithms are primarily data driven, without a priori knowledge of waveform and sensor position, representing a crucial step in developing a robust imaging system.