Time-resolved measurements of statistics for a Nd:YAG laser

Time-resolved measurements of the fluctuating intensity of a multimode frequency-doubled Nd:YAG laser have been performed. For various operating conditions the enhancement factors in nonlinear optical processes that use a fluctuating instead of a single-mode laser have been determined up to the sixth order. In the case of reduced flash-lamp excitation and a switched-off laser amplifier, the intensity fluctuations agree with the normalized Gaussian model for the fluctuations of the fundamental frequency, whereas strong deviations are found under usual operating conditions. The frequencydoubled light has in the latter case enhancement factors not so far from values of Gaussian statistics.     

Modeling of a Diode-Side-Pumped Nd:YAG Laser

We have developed a unique numerical laser model by use of a commercial physical optics software package. The experimentally measured lasing threshold, slope efficiency, power output distribution, and phase front have been derived. This model is particularly powerful for monitoring the effects caused by thermal distortions encountered in power scaling lasers. Extrapolations have been made through parametric studies to predict changes required in the laser design that would optimize the performance of the laser.     

All solid-state Cr:LiSAF laser

Many kinds of experiments about all solid-state Cr:LiSAF lasers have been reported. A tunable all solid-state cw laser having tunability over more than 100 nm was developed by using the spectrum selection self-injection locking (SSSIL) method in 1992. The authors realize tunable picosecond radiation from an all solid-state laser with 146-200 ps pulses in an 88 nm range. Also, 70 fs pulse generation was achieved using a Kerr-lens mode-locking pumped with an Ar⁺ laser     

Initial phase of laser-induced air optical breakdown: a new picture

Optical breakdown has been generated by focusing YAG laser radiation in the air. The laser radiation itself was scattered due to laser-induced air optical breakdown. Angular distributions of scattered radiation at 1064, 532, and 355 nm were measured. Analysis of the distributions has been performed in terms of Mie scattering. It has been assumed that scattering of laser radiation is due mainly to highly ionized plasma balls in the initial phase of air optical breakdown. The wavelength-dependent angular distribution has been analyzed with two parameters. The mean radius and the plasma frequency of the plasma balls have been determined by a least-squares fit procedure. Observed wavelength-dependent angular distributions are in good agreement with ones calculated by Mie theory.     

Efficient quasi-continuous-wave and passively Q-switched laser operation of a Nd3+:BaGd2(MoO4)4 cleavage plate

Pumped by a Ti:sapphire laser at 807 nm, efficient quasi-cw and passively Q-switched laser operations have been realized from a 1.1 mm thick, 1.2 at. % Nd(3+):BaGd(2)(MoO(4))(4) cleavage plate in a plano-plano cavity. When the absorbed pump power was 1060 mW, the achieved maximum quasi-cw output power was 580 mW. The slope efficiency and absorbed pump threshold power were 60% and 50 mW, respectively. Using a Cr(4+):YAG crystal with an initial transmission of 85% as the saturable absorber, a pulse laser with 3.0 microJ energy, 30 ns duration, and 52 kHz repetition rate has been obtained when the absorbed pump power was 1060 mW. The polarization characteristic and laser spectra of both the quasi-cw and passively Q-switched lasers have been measured.     

Stabilizing the spectrum of a femtosecond Ti:Sapphire laser

A new scheme for stabilizing the beat frequency of the interacting longitudinal modes in a femtosecond Ti:sapphire laser (Femos-1) has been developed and experimentally studied. The stability and frequency spectrum of mode beats in a modified laser have been monitored. A short-term instability of the beat frequency does not exceed 4.8 × 10^?8 (τ = 10 s) over a time scale of 10 min. The laser linewidth in the regime of self-mode-locking is ≤3 Hz at a laser spectrum width of 20 nm.     

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.     

Noise characteristics of a Nd:YVO(4) laser pumped by laser diode modulated at high frequency

We report, for the first time to our knowledge, on the noise characteristics of a Nd:YVO(4) laser pumped by a laser diode modulated at high frequency. We have investigated noise characteristics of a Nd:YVO(4) laser pumped by a laser diode that is oscillating in a stable multilongitudinal mode because of modulation by a high-frequency (several hundred megahertz) current. As a result, low-noise operations of -130 dB/Hz above frequencies of 1 MHz have been achieved. This noise level is comparable to the level obtained when pumping a Nd:YVO(4) laser with a laser diode that is oscillating in a single longitudinal mode. However, a noise peak corresponding to relaxation oscillations of the Nd:YVO(4) laser has appeared around a frequency of several hundred kilohertz.     

Diode-side-pumped 131 W, 1319 nm single-wavelength cw Nd:YAG laser

A diode-side-pumped high-power 1319 nm single-wavelength Nd:YAG continuous wave (cw) laser is described. Through reasonable coating design of the cavity mirrors, the 1064 nm strongest line as well as the 1338 nm one have been successfully suppressed. The laser output powers corresponding to four groups of different output couplers operating at 1319 nm single wavelength have been compared. The output coupler with the transmission T=5.3% has the highest output power, and a 131 W cw output power was achieved at the pumping power of 555 W. The optical-optical conversion efficiency is 23.6%, and the slope efficiency is 46%. The output power is higher than the total output power of the dual-wavelength laser operating at 1319 nm and 1338 nm in the experiment.     

Stable room-temperature LiF:F2 (+*) tunable color-center laser for the 830-1060-nm spectral range pumped by second-harmonic radiation from a neodymium laser

Simultaneous photostability and thermostability of a room-temperature LiF:F2(+*) tunable color-center laser, with an operating range over 830-1060 nm, pumped by second-harmonic radiation of a YAG:Nd(3+) laser with a 532-nm wavelength has been achieved. The main lasing characteristics of the obtained LiF:F2 (+*) laser have been measured. Twenty-five percent real efficiency in a nonselective resonator cavity and 15% real efficiency in a selective resonator cavity have been obtained. The stable LiF:F2 (+*) laser operates at a 1-100-Hz pulse-repetition rate with a 15-ns pulse duration, a 1-1.5-cm(-1) narrow-band oscillation bandwidth, and divergency of better than 6 × 10(-4). Doubling the fundamental frequencies of F2(+*) oscillation made it possible to obtain stable blue-green tunable radiation over the 415-530-nm range.     

Efficient energy transfer between Ce/Cr and Nd ions in transparent Nd/Ce/Cr:YAG ceramics

This paper reports the spectroscopic and laser characteristics of transparent ceramics of YAG:Nd co-doped with Ce and Cr. The ceramics were prepared by advanced ceramic techniques and showed more than 85% of transparency. Diode pumped laser oscillation performed at different output coupler transmissions (T) showed that a maximum slope efficiency of 16% was achieved for T = 3%. The cross energy transfer mechanism under violet laser diode pumping has been analyzed and the possible energy transfer mechanisms have been proposed using the various energy levels of the dopant ions. The emission lifetimes of the dopant ions at two different concentrations have also been found.     

高效率低阈值激光材料Nd:S-FAP晶体

报道了一新型高效率,低阈值激光晶体Ｎｂ：Ｓ－ＦＡＰ的激光特性,利用染料激光和ＬＤ作为泵浦源,分别研究了Ｎｄ：Ｓ－ＦＡＰ晶体激光器的脉冲和连续输出的激光特性,染料激光泵浦Ｎｄ：Ｓ－ＦＡＰ激光器的泵浦阈值为２．５ｍＪ,     

Intracavity frequency doubling and Q switching in diode-laser-pumped Nd:YVO(4) lasers

A highly efficient and compact Nd:YVO(4) laser is proposed. In cw operation, a single-longitudinal-mode output of 95 mW and a multilongitudinal-mode output of 435 mW have been observed at 1.06 μm with a 1-W diode laser. Using a KTP crystal in the short laser cavity, a green output of 105 mW was generated. A Q-switched pulse with a peak power of 230 W and a pulse width of 8 ns was obtained with the intracavity KTP crystal, which was used as both an electro-optic Q switch and a frequency doubler.     

Modeling of quasi-three-level lasers and operation of cw Yb:YAG lasers

We present modeling studies of quasi-three-level laser oscillators, the validity of which was revealed by Ti:Al(2)O(3)-pumped Yb:YAG laser experiments, and these results are shown to be in excellent agreement with the theory. As much as 75% slope efficiency was obtained with a hemispherical laser cavity. Previous modeling calculations of laser performance have been valid only for certain special cases, restricting application to TEM(00) Gaussian beam pumping and lasing profiles. This analysis may be applied to other longitudinally pumped quasi-three-level laser media in which the modes are not only TEM(00) Gaussian beams but also other higher-order transverse modes, including the top-hat pumping profile that can be used to model transverse pumping schemes.     

Efficient acousto-optic Q switching of Er:YSGG lasers at 2.79-microm wavelength

A flash-lamp-pumped Er:Cr:YSGG laser at 2.79-mum wavelength has been acousto-optically Q switched. The Q-switched pulse energy and duration depend on pump pulse level and relative Q-switching time. Limits of single-pulse operation with the given acousto-optic diffraction efficiency have been determined. Resonator length, position of the Q switch, and output mirror reflectivity have been varied to obtain high pulse energy and the shortest pulse duration in the TEM(00) transverse laser mode. A maximum single-pulse energy of 27 mJ and a minimum pulse duration of 120 ns were obtained with an output mirror reflectivity of approximately 25%. The highest Q-switched single-pulse energy amounted to 52% of the free-running, fundamental mode output pulse energy.     

Deep-ultraviolet Raman microspectroscopy: characterization of wide-gap semiconductors

We have developed a high-throughput deep-ultraviolet (DUV) Raman microspectrometer with excitation from a continuous wave (cw) laser operated at 244 nm that enables us to characterize thin surface layers of wide-gap semiconductors. This spectrometer system consists of a filter spectrometer for the rejection of stray light and a high-dispersion spectrograph combined with a liquid nitrogen cooled charge-coupled device (CCD) detector and extends the low-frequency limit of the observable spectral range down to 170 cm(-1). In the microscope we use a Cassegrain reflective objective for the collection of the scattered light and an off-axis mirror for introduction of the excitation laser light. DUV Raman spectroscopy has been applied for studying wide-gap semiconductors including SiC and AlGaN epitaxial films and shallow implanted layers of these materials. Raman spectra of various crystals have also been measured for examining the performance of this system. Resonance enhancement of Raman bands has been observed for several semiconductors, and the results are discussed.     

Consideration of Stimulated Raman Scattering in Yb:Sr(5)(PO(4))(3)F Laser Amplifiers

The stimulated Raman-scattering (SRS) gain coefficient has been measured quantitatively for the first time to our knowledge in Yb:Sr(5)(PO(4))(3)F to be 1.23 ? 0.12 cm/GW at 1053 nm. These data, along with surface and bulk losses, feedback that is due to surface reflections, gain saturation, and bandwidth, have been applied to a quantitative model that predicts the effects of SRS within a laser amplifier system where the laser gain media show SRS gain. Limitations and impact to the laser amplifier performance are discussed, along with possible techniques to reduce SRS loss.     

Frequency Stabilization of a Ho:Tm:YLF Laser to Absorption Lines of Carbon Dioxide

A single-frequency Ho:Tm:YLF laser, operating at an eye-safe wavelength of 2 mum, has been developed with tuning characteristics optimized for spectroscopy of absorption features. The laser frequency was stabilized to three different absorption lines of carbon dioxide by a wavelength modulation technique. Long-term frequency drift has been eliminated from the laser, and shorter-term jitter has been reduced to within 13.5 MHz of the absorption line center. This stabilized laser is an ideal injection seed source for a differential absorption lidar system for measurement of atmospheric gases.     

Laser-Induced Graphene on a Polyimide Film: Observation of the Photon Drag Effect

Technical Physics Letters - Film structures of porous graphene have been produced by irradiating a polyimide film with focused radiation of a continuous CO2 laser. The generation of nanosecond...     

EXPERIMENTAL TECHNIQUES TO CUT AND WELD COPPER BY LASER - A REVIEW

This paper reports on the cutting and welding of copper sheets using a CO₂ laser. For the cutting process, the experimental data from tests on 0.2 to 4.0 mm thick copper sheets with a 2 kW CO₂ laser are described. The behavior of the critical cutting speed V, cutting widths a, the product V × b and the melted volume versus the thickness (b) for a 2 kW CO₂ laser using different focusing lenses has been investigated, The cutting speeds have been found to be significant and micrographic examinations have shown that the laser cutting quality is good. The laser welding of copper sheets is possible by overlapping layers of cupric oxide, CuO, with a small quantity of cuprous oxide, Cu₂O grown under laser beam irradiation. This experimental approach, similar to the one used for the cutting process, allows one to increase the copper surface absorption of the laser radiation. The weld tests done in this way have shown a bad quality of the butt joint; in fact, a number of inclusions in the melted zone and growth of the copper grains surrounding the weld have always been observed. Another experimental technique has also been tested using a better coating to increase surface absorptive power without producing weld defects. The first results are interesting, though the research is still in progress. Finally, by using e pulsed Nd-YAG laser and the same coated samples - cited above - some good welds have been obtained.