We have measured the opening time of the so-called "blast shutter", presently used as an isolator in high-power laser systems. The shutter consists of a 275 A thick aluminum film deposited on a transparent plastic film 12 4 thick. The aluminum film is suddenly removed by exposing it to high-power pulses from a Nd:glass laser (X = 1.06 4). We have used pulses 50 ps in duration that delivered between 0.5 and 3 J/cm2 of energy onto the aluminum film. The absorbed energy superheats the film and turns it into a rapidly expanding cloud of aluminum vapor. A blue laser beam from a CW argon laser passes through the shutter and is detected by an ultrafast streak camera, set for 50 ps resolution. With this arrangement 10-90% shutter opening times varying from 0.8 to 4 ns have been measured, the former occurring at laser pulse energy densities of ≈ 2 J/cm2.
Laser-fusion requires diagnostics of high-density, high-temperature plasmas on the pico-second time scale. To this end a proximity-focused streak camera has been under development. An x-ray version of this device has been constructed and tested using x-rays generated by irradiating microballoon targets with a two-beam Nd:glass laser. Results indicate the pro-totype to be of high sensitivity with temporal resolution of 2.5 to 3 ps. Later production cameras based upon this design are expected to give sub-picosecond temoral resolution for both x-ray and visible light. The camera is simple, compact, rugged and vacuum compatible. It has proved 98% reliable in over 350 laser shots. Applications to other disciplines are being studied and will be discussed.
It was Courtney-Pratt's use of a deflectable image converter in l949, for measuring the high-speed optical characteristics of explosives, which first allowed the sub-microsecond time domain to be penetrated. Since that time,important applications have arisen for high speed chronography detectors and instruments in fields such as biology, chemistry, communications, materials sciences, nuclear physics and quantum electronics. At the present time, advances in the understanding of basic high-speed physical processes in these and other fields are proceeding hand-in-hand with advances in the technology of high-speed photography. In addition, high-speed detector improvements allow new tasks to be performed or greater accuracy to be obtained.
Temporally, spectrally, and spatially resolved x-ray emission diagnostics are important tools in the study of the heating and compression of laser fusion targets by sub-nanosecond laser pulses. The use of the Livermore 15 psec resolution x-ray streak camera to make such measurements is reviewed. Temporal histories of spectrally resolved x-ray emission in the 1-10 keV range have been obtained. These data have served to further define the x-ray streak camera as a quantative diagnostic tool and have also provided data relating to the absorption and compression phases of laser heating. The x-ray streak camera has been used in conjunc-tion with a specially designed pinhole imaging system to temporally record images of laser compressed targets with a spatial resolution of approximately 6 pm. Implosion characteristics are presented for experiments with glass microshell targets. The concept, development, and testing of an ultrafast framing camera for full two-dimensional time resolved imaging is discussed. A prototype camera, based on the image dissection-restoration concept, has achieved an approximately 200 psec frame period with a resolution of 50 μm.
A new kind of illumination method converts a streak camera into a remote profilemeter. The object is illuminated by a short pulse (thickness cΔt). The backscattered radiation is focussed to form an ordinary image. A slit in that image plane confines our attention to a line across the scene. The slit is imaged onto the photocathode of a streak camera. The streaked record is the depth profile along the line of the slit. Depth resolution is about cΔt/2 (around a millimeter for conveniently available components). With a slight modification we obtain an absolute range finder for each point in the scene with the absolute range accuracy still about cΔt/2. Another modification minimizes the effects of trigger jitter and limited time-bandwidth product of the streak camera. Several applications are noted.
Rapid frame rate motion picture data is being used in two diverse areas of biological investigation. A study of the bat population decline at Carlsbad Cavern, New Mexico, requires frequent estimates of the size of the bat population. Motion pictures are taken at intervals during an exit flight and are used to estimate the number of bats leaving the cavern on a given evening. Rapid frame rate motion pictures are also used to analyze the locomotion mechanisms in different species of bats. Electrodes implanted in muscles permit simultaneous recording on motion picture film the movements of a bat and the concurrent electrical activity of a contributory muscle. To permit visualization of skeletal movements during flight, steel wires are firmly implanted in bones and pectoral girdle and exteriorized. Reflective paint applied to the tips of the wires increase their visibility in rapid frame rate motion pictures taken of the bat in flight.
The application of picosecond optical range-gating techniques to ophthalmology is described. By directing picosecond light pulses into the eye and detecting the backscattered pulses with an ultrafast Kerr cell shutter it is possible to: 1) measure the location of index discontinuities and cataracts with a resolution of 1 mm; 2) measure scattering particle size distributions in the micron range; and 3) visualize the retina through a dense cataract. The techniques have been successfully tested on simulated eyes and are being used on animal eyes in vivo. Another application discussed is the extension of the ultrafast gating technique to picosecond X-ray cinematography.
A 7 nsec exposure time magneto-optic camera system has been constructed for observation of dynamic magnetic phenomena such as occurs in magnetic bubble domain devices. The system employs a super-radiant nitrogen pulsed dye laser as a light source, a polarizing microscope to make the magnetic features visible, and a low light level T. V. system for recording the observed phenomena. The laser pulse is synchronized within 1 nsec to the dynamic magnetic process to be observed and the video system framing rate may be synchronized to the laser so that each recorded video picture is a record of one instant in one dynamic process. A coil assembly and drive electronics were constructed to permit optical access to the magnetic sample and simultaneous application of high frequency (to 1 MHz) rotating magnetic fields (to 60 Oe) required to drive a bubble memory. To make the magnetic domains, which may be smaller than one micron, visible, polarizing optics and the Kerr or Faraday magneto-optic effects are employed. Techniques for optimizing the visibility of magnetic domains in such a system are discussed in detail. The system has made possible the visual observation of high speed magnetic bubble domain phenomena and has contributed significantly to the understanding of bubble domain dynamics.
Application of an electric field to PLZT optical ceramic material causes an electrically induced bifringence. When placed between crossed polaroids the device may be used to continuously vary the beam transmittance. Construction and performance details are discussed,
This concept offers an entirely new approach to High Speed Photography as described in U. S. Patent No. 3,613,978. Phased eccentric rollers move the film intermittently, and continuously control captive loops unyieldingly; no spring loaded rollers with limited frequency response are used. Registration pins lock the film during exposure. Thus pull down claws, free loops, and associated instability problems at high speed operation are eliminated. Smaller roller eccentricity -- only 1/16 of pulldown dimension -- permits easy balancing, low eccentric bearing loads and mechanism strain. Unusual geometric relations permit easy adjustment for film pitch variations.
The Hexadecimal Data Recording System (HDRS) represents the first application of microprocessor technology in data acquisition with photographic instrumentation cameras. Expanding the data recording capability of both intermittent and continuously moving film cameras was the principal design objective. Additional design goals included: 1. The ability to accept various external digital signal inputs and to record this data on film, simultaneously with the pictorial information. 2. Provide a practical retrofit capability for most types of instrumentation cameras currently in use. 3. Simplicity of system design and enhanced operational reliability in the field. These design objectives have been met and the system hardware demonstrates that a typical instrumenta-tion camera can fill an expanded role considerably beyond its traditional use. Considerations involving the use of a microprocessor and the resulting impact of computer intelligence are discussed.
The microwave terminals, satellite ground stations, and CATV industries demand wideband, high-frequency communication links. A very-low-mesa-stripe Gai_xAlxAs-Gai_yAlyAs double-heterostructure (DH) injection laser diode (ILD), and a silicon avalanche photodetector (APD) have been utilized in a 500-MHz fiber-optic system to demonstrate high-frequency feasibility. The ILD, capable of being modulated up to 700 MHz with 1.25-dB/octave rolloff, coupled 4.9 mW into a single Corning low-loss fiber with microlens formed at the input end. Above 700 MHz, the distortion becomes severe due to relaxation oscillation. The frequency-dependent nonlinearity of ILD, which can be compensated by a special circuit design, has been analyzed by Volterra series. Using a gain equalization circuit in both the ILD transmitter and APD receiver, the system has very flat response up to 270 MHz and usable response to 500 MHz (S/N = 56 dB). Above 270 MHz, the gain is reduced due to the characteristics of the APD. With two tones (90 and 125 MHz), the system has an S/N (each tone) of 58 dB in 100-kHz bandwidth measurements. Without nonlinear compensation, the second- and third-order intermodulation products (IMP's) are 24 dB below the carrier. Presently, with special compensation network, IMP's of 33 dB below the carriers are obtained.
This paper discusses recent progress toward the development of an electronics measurement capability with picosecond time resolution using picosecond optical pulses. Devices utilizing the transient photoconductivity produced by the absorption of picosecond optical pulses in high speed semiconductor circuits have been demonstrated which are capable of performing elementary electronic operations such as switching, gating, sampling, pulse generation, etc. Applications to electro-optic gating, high speed electronic sampling, and measurement of semiconductor relaxation and transport phenomena will also be discussed.
The lunar ranging station at the University of Texas McDonald Observatory has made more than 1800 range measurements to the four lunar retroreflectors during the first six years of its operation. Each range consists of a normal point constructed of from 5 to 20 single photoelectron returns. Normal point accuracies to about 4 parts in 1010 (± 10 cms) have become routine. The availability of excellent commercial timing equipment, similar to that used for nuclear time-of-flight experiments, means that the error budget for such a measurement is primarily dependent on the width of the transmitted laser pulse (currently 3 nanoseconds FWHM). Second generation systems using mode-locked, subnanosTRond lasers can probably achieve routine normal point accuracies approaching one part in 10 (± 2 cms). High speed pockel cells, capable of slicing sharp edges on relatively long laser pulses, may permit such accuracies to also be realized with conventional Q-switched lasers.
We review the recent application of picosecond laser techniques to the study of photosynthesis. Two techniques are emphasized. In the first a streak camera is used in conjunction with a mode locked laser to determine the 'exciton' migration time to the photosynthetic reaction center. In the second a novel nonlinear optical technique is described which enables certain deductions to be made about the topology of the photosynthetic unit. Bacteria and higher plant data are presented.
A technique is described for obtaining short exposure (≈8 ns) high resolution photomicrographs of electrically exploded bridges using a pulsed laser for bridge illumination and band-pass filters to eliminate the intense self light. Two cameras are described, one for a small field of view (til mm) and one for a relatively large field of view (≈20 mm). A carbon disulfide cell and a fiber-optic light guide are used to essentially eliminate speckle, which normally limits the resolution of laser photographs of diffuse surfaces. A series of photomicrographs showing the detailed burst characteristics of both flat and round bridges are shown.
Picosecond lasers can be used to observe the kinetics of two rapid processes in solution: relaxation of excited molecules prior to Stokes-shifted fluorescence and relaxation of oriented molecules. Experimentally, the measurements are similar. An ultrafast shutter driven by a picosecond pulse and an optical multichannel analyzer (OMA) enable the rise of fluorescence to be observed during a single, picosecond exciting pulse. For excitation at 355 nm risetimes are: 4.2 ± 2.2 psec for esculin, 1.0 ± 2.2 psec for dimethyl POPOP, and 5.3 ± 2.2 psec for tetraphenylbutadiene. The shutter is an optical Kerr cell in which an intense pulse induces birefringence by orienting the molecules in the liquid. As orientational relaxation occurs, birefringence decays. Using the OMA to observe a scattered picosecond pulse through the shutter enables the decay to be measured in a single shot. Rotational relaxation times for pure liquids and mixtures vary from 2 psec for carbon disulfide to 21 psec for nitrobenzene.
The primary emphasis of this paper is to show that the laser interferometric technique can be a valuable electro-optical measuring tool in the study of material response to the 2D shock wave phenomena found in hypervelocity impact. Preliminary experiments conducted at Effects Technology, Inc. on several nosetip and heatshield materials indicate that laser interferometry is a useful high speed measurement technique for the study of two-dimensional shock wave effects. The two-dimensional shock wave generators for these initial tests were single particle hypervelocity impacts. The specimens were impacted normal to the front surface by a 1000 pm glass sphere at velocities ranging from 3660 m/sec (12,000 ft/sec) to 4880 m/sec (16,000 ft/sec) while the laser beam continuously monitored the rear surface of the specimen. The laser interferometer records the free surface motion of the material as the transmitted shock wave is incident on the rear surface. Consequently, a graphical representation of the shock pulse reaching the specimen free surface can be reconstructed from the interferometric data record. Data processing and analysis of this type leads to the characterization of the dynamic two-dimensional shock wave response of the material.
The Photogrammetric System design objectives are stated. Descriptions of the camera calibration equipment and calibration procedures are given. A detailed description of the Simulated Underwater Partial Launch System (SUPLS) is presented with special emphasis on the high speed camera system data reduction.
A photographic handbook called The Photographers Guide presents a systematic and quantitative method for selecting camera systems and their conditions of use. Its purpose is to ensure that the required level of object-space resolution is successfully recorded. It features a unique nomagraph which relates: resolution in object space, object distance, lens focal length and image plane resolution. Typical field performance data is given for 35mm SLR camera systems. Other data tables cover effect such as handheld cameras at slow shutter speeds, motion, atmospheric effects and depth-of-field degradation. The handbook can be applied to a broad range of photo-optical instrumentation tasks.
An exploratory development of a 1 Gbps single-pass single-unit (unmultiplexed) modulator for use with a mode-locked and frequency-doubled neodymium YAG laser in a space laser communication system was conducted for the Air Force Avionics Laboratory. The modulator was to operate at data rates up to 1 Gbps with a 0.53 micrometer laser input. The performance goals were (1) a static extinction ratio of 100 to 1 or greater, (2) a worst case dynamic extinction ratio of 30 to 1 or greater with a 1 Gbps pseudorandom code input, (3) 100% depth of modulation, and (4) at least 80% transmission of the beam input power statically. This effort consisted of a 1 Gbps 0.53 micrometer modulator and driver in breadboard form used as a laboratory tool to demonstrate the feasibility of this modulator design concept. The modulator development utilized lithium tantalate crystals in four different configurations. The modulator drivers were designed with both thin film hybrid and discrete component input stages with the dual output stage using only discrete components. Various modulator and modulator driver combinations were used in the dynamic performance evaluations. The performance of the best modulator and modulator driver, met most of the design goals. The modulator driver had 20 volts ±1 volt outputs with timing inaccuracies of ≤ ±175 ps including PN generator timing inaccuracies of ≤ ±70 ps. The driver had rise times between 400 ps and 500 ps. The modulator had two 10mm long lithium tantalate crystals tapered in the c-axis in order to reduce the switching voltage by 20% which resulted in a dc half-wave switching voltage of 19.8 volts at 0.53 pm wavelength. This modulator had a static extinc-tion ratio of 90:1 and a worst case dynamic extinction ratio of ≥ 22.4:1 with a 1 Gbps pseudorandom code. The depth of modulation was 100% since the driver applied full half-wave switching voltage to the modulator. The modulator (crystals only - single pass) transmitted 81.5% of the beam input power statically.