Transient changes of erbium ion level populations in Yb:Er:phosphate glass caused by flashlamp or Nd:glass laser excitation were measured. Dependence of laser pumping efficiency on laser pulse duration was studied for two samples with different Er3+ ion concentrations. Diffusion bottleneck due to low erbium concentration is shown to influence considerably the Yb-Er sensitization process.
Behavior of radiation of Nd:YAP and Nd:YAG in a resonator with extremely low Q-value have been studied. The light pulses of the form discrete spikes around 1.08 micrometers have been observed using a relatively low pumping energies in Nd:YAP. The formation of these pulses has threshold character. Additional measurement such as second harmonic generation, far field distribution and spectral behavior have shown that emitted pulses have a typical laser character. Derived value of threshold gain parameter with material losses (g0 - (alpha) ) for threshold energy is 0.581 cm-1. No similar effect was observed for Nd:YAG, even for four timeshigher value of threshold energy than Nd:YAP. Obtained results demonstrate the cooperative effects of Nd3+ ions in Nd:YAP through a correlation between electromagnetic and crystal field.
Figure 1 represents schematically the possible sources of pointing faults. First set of faults is connected with optical distortions and misalignements; these faults exist even when the target does not move. Here are: i - atmospherical distortions caused by turbulence, wind, and sometimes by thermal blooming; L2 distortions and misalignements of optical systems (both receiving, affecting the accuracy of target position determination, and transmitting, thus deteriorating output beam quality) ; E3 -faults that are usually connected with a discrete nature of coordinate photoreceptor; E4 -faults and distortions of the laser optical path: dynamic distortions in amplifiers, scanning systems limited accuracy, misalignements and vibrations of the optical elements, etc. It is worth to note that -2' and L4arenonlinearly dependen on the laser beam power. Second set of faults is connected with temporal delays; they are most dangerous when pointing to the moving targets. Here are: T1 - timeof double light pass to target; T2 - time of obtaining signal from photoreceptors; T3 - time of signal processing; T4 - response time of deflectors. So to achieve the high-stable laser beams pointing means to minimize the values of all listed factors. In some cases physical limitations exist (e.g. one can not overcome the diffraction limit for A2; or the light speed limit for T1 , and it easy to see that for long-distance cases this fundamental limitation becomes the strongest) ; in other cases the break-through lies in the development of non-optical technologies (as, say, in computing technology for T3). Thus our efforts were to find some possible and "optical" ways in order to improve the accuracy of laser beams pointing.
Lithium fluoride crystal containing F2- color centers (LiF:F2-) is a room temperature stable, with annealing temperature higher than 400 degree(s)C; long lifetime, over ten years; near IR, 0.8 micrometers to 1.2 micrometers saturable absorbing color centers crystal. It could be used to passively Q-switch or mode-lock solid state Nd doped laser systems. What is more, due to the better heat dissipating capability of this crystal compared to the saturable absorber dye sheet with cellulose acetate host, it could be used to passively Q-switch Nd laser systems up to 30 pps repetition rate without any forced cooling.
We have developed an accurate simulation program to predict the performance of flashlamp- pumped Titanium Sapphire (TiS) lasers. The program has been benchmarked to several experimental lasers with energy outputs from 0.1 to 1.0 Joules per pulse. The results for lasers operating in both long-pulse and Q-switched modes agree with experimental results to within 20%. We have used this program to explore energy scaling of TiS laser oscillators from 1.0 to 10.0 Joules using realistic values for lamp pulse energy loading and TiS material Figure-of- Merit (FOM). We present here results of this energy scaling as explicit functions of laser rod diameter, length, doping level, Figure of Merit, use of dye converters, pump pulse length and number of lamps. The results indicate that with proper lamp coupling, via reflectors, etc., lasers with pulse energies greater than 10 Joules are possible with electrical-to-output efficiency greater than 1%.
We have measured the time-dependent transmittance of 'orange plastic' samples composed of the dye 1-Phenylazo 2-Napthalenol embedded in both polymethyl methacrylate (PMMA) and polycarbonate at various dye concentrations. The spectrophotometric transmittance below 520 nm is measured to be less than 0.01% for the PMMA samples. However, a 6.4 mm thick PMMA sample containing 0.008% dye concentration reached a steady-state transmittance of 0.5% in 15 seconds for samples irradiated with continuous wave 514.5 nm light at 12 mW/cm2. The transmittance reached a steady-state of 11% in 2.5 seconds when irradiated with 514.5 nm at greater than 600 W/cm2 incident. This represents a three order of magnitude increase in the transmittance at relatively low irradiance levels. In contrast, a 6.4 nm thick PMMA sample containing a dye concentration of 0.03% continued to transmit less than 0.01% with increased irradiance until the material reached damage threshold. We report ground-state absorption curves and transmittance versus time measurements for dye concentrations ranging from 0.008% to 0.15% in PMMA and polycarbonate. We compared the steady-state transmittance at 514.5 nm to the incident irradiance. We propose possible mechanisms associated with the nonlinear transmittance characteristics of 1-Phenylazo 2-Napthalenol.
In contrast to laser cutting and welding, laser drilling is rather unknown for industrial applications today. A main reason for this is the poor processing quantity. In this paper a special Nd:YAG-laser system will be introduced, which is well suited for drilling applications, due to high beam quality as well as high output power. In combination with an acoustooptical Q-switch, high quality drillholes in the micrometers -range have been achieved. Different parameters of the laser process cause variable hole diameter in steel and ceramics. This paper gives some examples, and the advantages and disadvantages of drilling micro holes using a laser are discussed.
Various structures like molds, cavities and textures can be machined in hardest and non- conductive materials using pulsed laser radiation. Possible disadvantages of the process are variation in removal quality and partial reagglomeration of the molten material. In this paper, results of investigations (done with pulsed Nd:YAG-radiation) on the influence of process parameters and on the removal strategy will be shown. The machined result is characterized by the removal rate and the extension of heat affected zones as well as geometric accuracy and surface roughness. Process improvements can be achieved with preselected parameters, remelting of the material surface and an on-line process-control.
Two internally folded, scalable laser resonator designs have been demonstrated. One, based on an isosceles right angle prism, was pumped along three axis simultaneously with 3.73 W at 808 nm. It produced 1.3 W at 1.06 (mu) with no evidence of thermal saturation. In addition, good second harmonic conversion efficiency was achieved and 128 mW of low noise output was obtained. The second design is based on a penta-prism. Using five single stripe laser diodes to pump along three separate axes, 4.16 W of absorbed power produced 2.3 W in the TEM00 mode. The slope efficiency was 56%, the optical conversion efficiency was 55%, and the output was linearly polarized. No evidence of thermal saturation was observed up to the maximum pump power used and high conversion efficiency was maintained over the entire range of pump power. The pump threshold power was 48 mW. With an intracavity KTP crystal, 341 mW of cw amplitude-stable output at 532 nm was generated.
Continuous tunability and high efficiency are obtained from an intra-cavity double Optical Parametric Oscillator (OPO) pumped by a frequency-doubled diode-pumped Nd:YAG laser. The OPO is tunable from 760 - 1040 nm with 30% efficiency, giving 380 - 520 nm tunability after intra-cavity doubling with 40% efficiency.
McDonnell Douglas Electronic Systems Company (MDESC) approach to developing 1.5X micron lasers have been to either diode pump Er:Glass or to use Nd hosts to pump optical parametric oscillators (OPOs). A 1.57 micron Optical Parametric Oscillator (OPO) from a multimode 1064 nm Nd:YAG slab laser has been demonstrated. Using KTP as the nonlinear crystal, 39 mJ of 1.57 micron has been achieved with 1064 nm pump input of 200 mJ. The system had a wall plug efficiency > 1%.
A single component continuous wave (CW) heterodyne laser Doppler anemometer (LDA) was constructed based on solid state technology for use in fluid dynamic research. The system design was motivated by the need for a miniature system capable of withstanding harsh operating environments. Such environments are often unavoidable when measuring high temperature combustion flows and when performing measurements in the field. With the recent advancements in solid state laser diodes and solid state avalanche photo diodes (APD), it is possible to construct miniature laser Doppler anemometers employing only solid state technology. Such systems have the advantages of small size, light weight, low power consumption, low cost, and ruggedness. The subject of the current research was to evaluate a visible laser diode's abilities and limitations in such a miniaturized LDA system. A basic one dimensional LDA was designed, constructed and thoroughly tested employing a 10 milliwatt visible (670 nm) laser diode. The problems specifically associated with the use of a laser diode as a source are discussed, and their solutions presented. Data for the LDA evaluation measurements in a free jet facility is presented, and the results are compared to measurements obtained by hot-wire and five-hole probes. The miniature solid state LDA system was found to possess accuracies of 2% for mean velocities and accuracies of 5 - 20% for RMS turbulent velocities. Overall, the miniature LDA system with the solid state laser diode was found to be capable of accurate fluid dynamic measurements, and it appears to hold promise in enabling LDA measurements in before impractical situations.
Continuous-wave modelocked operation of a Tm:YAG laser is demonstrated in the 2 micrometers wavelength region. The Tm:YAG laser is actively modelocked with an acousto-optic modulator to generate stable, transform-limited pulses of 35 picosecond duration at a repetition rate of 300 MHz.
We review the state of the art in developing passively Q-switched and mode-locked 2-micrometers lasers. Passive Q-switching was demonstrated using an InGaAs saturable absorber. An experiment to demonstrate passive mode locking using a diode-pumped 2-micrometers laser and similar semiconductor saturable absorbers is in progress.
The advances in new nonlinear optical materials and laser technology have made it attractive to generate 2-micrometers power using standard 1-micrometers laser drivers and optical parametric frequency down-conversion techniques. In this paper we review the status of two pulsed sources of 2-micrometers power including low power, tunable, single-frequency (200-MHz bandwidth) device, and a high-power, synchronously-pumped, efficient (62% conversion of 1- micrometers to 2-micrometers power) degenerate optical parametric oscillator.
A single-mode flashlamp pumped pulsed YAG:Nd laser with the optical degenerative feedback was constructed and investigated . Single-mode stable operation was retained at 25% excess of the rate of pumping above the threshold with relatively high efficiency 0. 4%.
A laser altimeter based on the time of flight principle has been developed to be put on board a gondola of a balloon drifting in the atmosphere of Mars. The light source is a PGT:Nd solid state laser ((lambda) equals 1.067 micrometers ) which emits pulses about 10 ns wide at a repetition rate of 0.2 Hz, the energy of each pulse being about 7.5 mJ. Special attention was paid in the development work to minimizing the size, weight and power consumption of the altimeter. Thus its weight is 450 g and the average power consumptions of the electronics and laser have been reduced to about 30 mW and 0.6 - 0.8 W, respectively, by switching on the power supply to the measurement and interface part only during the 50 ms measurement period. The time interval between the transmitted and received signal is measured digitally by counting clock pulses obtained from a 100 MHz oscillator. The measurement range and single shot resolution are about 6 km and +/- 1.5 m, respectively. The laser altimeter contains two peak detectors to measure the amplitudes of the transmitted and received pulses for recording of the albedo on the surface of Mars. Test results show that the altimeter is capable of operating in a temperature range of -80 degree(s)C - +60 degree(s)C and at an air pressure of few torr. The minimum average reflection coefficient of the Martian surface is about 0.1 which enables the measurement range of 13 km if the minimum signal to noise ratio of the measurement is about 10.
Optical gain and photostability have been investigated for several orange/red rhodamine laser dyes (RLDs) doped in the polydimethylsiloxane and tetraethoxysilane derived organically modified silicate (PT-ORMOSIL) composites. The RLDs in PT-ORMOSILs exhibit gain and stability comparable to those in methanol solution while substantially better than in the PMMA matrix. Broadband laser oscillations have been achieved in a free-running resonator with Rh610/PT-ORMOSIL as the gain medium. The lasing threshold and slope efficiency are found to be approximately 8 (mu) J and approximately 30%, respectively.
The characteristics of energy processes in concentrated Er3+ system and their effects on the stationary three micron laser emission are discussed. It is shown that in certain conditions, valid for a broad range of concentrations, the laser equations could be solved analytically, the solution allowing to study the influence of various parameters on the laser emission. This revealed that a crucial role in determining a positive pump effect is played by a figure of merit that depends on the ratios of up-conversion rates from 4I11/2 and 4I13/2 levels and of the fractional thermal populations for the crystal field components involved in emission. In given pump conditions, the restrictions imposed on the figure of merit limit the emission wavelength range and the efficiency. The emission in Er3+ systems co-doped with Cr3+ is also discussed. Cr3+ co- doping not only improves the pump efficiency, but modifies the whole chain of energy transfer processes, leading to the extension of the laser wavelength range.
The possibility of sensitization of rare-earth laser active ions with infrared (especially two- micron) emission by Fe3+ is discussed. The spectroscopic and luminescence decay measurements on Fe, Tm or Fe:Tm doped GGG or YAG show that a very efficiency energy transfer from Fe3+ in tetrahedral sites to Tm3+ takes place showing prospects for new sensitization schemes.