(Modern Optics Laboratory, Department of Physics, Shandong Normal University, Jinan 250014, China The passively Q-switched all-solid-state laser pumped by laser diode (LD) is an ideal light source for obtaining nanosecond and sub-nanosecond pulses with high repetition rate, and has a simple structure. The advantages of small size, long life, low cost and high efficiency, have wide application prospects. Pumping Nd with LD:GdV04 Crystal cavity Cr4+:YAG passively modulating GdVCXt is an Nd3+ matrix crystal that is isomorphous with YVOd. The crystal is a laser medium well-suited for end-pumping a semiconductor laser, and has a completely similar laser performance as Nd:YV04 Nd:GdV04, but its absorption coefficient and stimulated emission cross-section are much larger than those of the Nd:YV4 crystal, and The thermal conductivity in the (110) direction is much higher than that of Nd:YV04.Cr4+:YAG is an ideal passive Q-switch for high power, high repetition rate and small full-cure lasers.The research work in this paper is to pump Nd:GdV4 crystals with LD. The cavity Cr4+:YAG is passively tuned to obtain an output beam with a smaller divergence angle. We use a flat-to-resonant resonator. The pump source is OPDC015-808 with an active semiconductor dopant concentration of 1.3%. The loss of the part, Nd:GdV04 crystal is also used as a mirror cavity, plated AR808nm and HR1064nm two-color film, the other side of the AR1064nm. The output mirror is a transmittance of 20% of the plane mirror, Cr4 +: YAG bubble and the absorption of the initial transmission rate 60%. At a pump power of 8W, we obtained a 1064nm quasi-CW output with an average power of 1W. After adjusting the cavity mirror to obtain the best 1064nm output, place the focusing lens next to the output mirror at its focus. KTP crystals were placed, KTP crystals were used for phase matching, and 1064nni/532run two-color antireflection coatings were plated on both sides. At a pump power of 8W, an average output power of 172mW was obtained at 532nm, and the KTP crystal was adjusted optimally. Green light output, and then placed close to the right side of the KTP crystal BB0 crystal, using BBO crystal type I phase matching to obtain the sum frequency (1064nm+532nm->355nm) output, in order to obtain high conversion efficiency, we adjust the KTP crystal, make it The fast axis and the optical axis of the Nd:GdV04 crystal are 45, and the BBO placement angle is carefully adjusted to obtain the highest harmonic conversion efficiency.The UV output can be obtained after prism splitting, and the UV is also obtained at a pump power of 8W. Frequency (355run) 20mV output, pulse energy 1.4p, 10ns pulse width, repetition frequency of 14kHz, 143 W peak power. This laser structure is simple, good stability, is an effective way to obtain the ultraviolet light output.
Ultraviolet Laser Zhang Fengchuan (Department of Computer and Information Science, Linyi Normal University, Linyi 276065, China) Du Jianxin, Liu Jie, Jia Yulei, He Jingliang (Department of Physics, Shandong Normal University, Jinan 250014, China) Infrared lasers such as Nd:YAG, C02, etc. The spatial resolution and high photon energy, which are easily absorbed by most materials, can directly destroy the chemical bonds of the atomic combinations of the connecting substances without causing carbonization effects to the surroundings. There are important applications in microprocessing such as engraving, marking, trimming, circuit board cutting, and drilling.
Currently, most high-peak-power, high-repetition-rate all-solid-state ultraviolet lasers use semiconductor lasers to pump neodymium ion crystals. The acousto-optic Q-switch generates quasi-continuous fundamental waves and then doubles, triples or quadruples to obtain 355 nm or 266nm UV laser. In this paper, we propose a new technology route, using Cr4+:YAG saturable absorbers instead of acousto-optic Q switches, KTP cavity multiplication, use BBO as quadruple frequency outside the cavity, so as to obtain 266tun UV laser output.
15W fiber-coupled semiconductor laser 0.7at%.04+: YAG saturable absorber has a pass length of 2.6mm and a static transmittance of r=60%. A simple flat-flat optical resonator is used. The output coupling mirror is 1064mn high. Reverse, highly transparent to 532nm. When the pumping power is 9.2W, the average power of '532nm green light is 600mW. The pulse repetition frequency is 25kHz and the pulse width is 18ns with SiPIN fast response photocell and 200MHz storage oscilloscope. After focusing by a BBO crystal/=50 mm lens, the 532 nm doubler produces an ultraviolet 266 nm laser output with a maximum average power of 38.4 mW. The entire system is compact and the output is stable and reliable.
Phase Control of Non-Reversal Optical Amplification Caused by Vacuum-induced Interference Effect WU Jin-hui, JIANG Yun, GAO Jin-yue (College of Physics, Jilin University, Changchun 130023, China In recent years, atomic systems with near-degenerate energy levels have received extensive attention. Under the action of the radiation field, interference occurs between spontaneous radiation from the same upper level to two near-degenerate lower levels (or from two near-degenerate upper levels to the same lower level), It is a vacuum-induced interference effect.It is worth noting that the existence of this interference effect requires that the corresponding two dipole matrix elements be non-orthogonal, otherwise the effect is zero.
In the past, when studying such atomic systems, people's main concern was the effect of vacuum-induced interference on the spontaneous emission characteristics and absorption characteristics of the system.
In this paper, we focus on the effect of this special interference effect on the system gain characteristics. We have found that, in addition to the enhancement of the non-particle inversion gain of the detection field, this effect also leads to the dependence of the non-inversion gain on the phase difference of the coherent field.
Here we are studying a /3-type three-level atom system with near-degenerate energy levels. A strong coherent field acts on a dipole-allowed transition, resulting in the necessary coherence between the corresponding energy levels. A weak coherent field is used to detect the gain on another dipole-allowed transition. At the same time, a weak incoherent pump acts on the probe transitions so that the necessary distribution of the population number exists at the highest energy level.
With the dipole approximation and rotation wave approximation, we obtain the analytical solution of the gain coefficient of the detection field by solving the density matrix equation of the steady state system. From the analytical solution, it is found that due to the presence of vacuum-induced interference effects, the absorption or gain of the weak detection field is no longer only related to the coherent field strength (amplitude) and frequency, but also depends on the phase difference between the coherent fields. The absorption or gain of the detection field consists of three components: the difference in the number of particles, coherent excitation, and vacuum induction. When the incoherent pumping is sufficiently weak, the contribution of the particle number difference term is always negative, so under the positive contribution of the latter two terms, we get the no-particles number inversion gain. Among them, the vacuum induction term is an additional addition to the conventional nondegenerate atomic system. Through analysis, it is not difficult to find that the contribution of vacuum induction is much greater than the other two. This means that due to the presence of vacuum-induced interference effects, we will obtain greater detection field gains.
This enhanced detection field gain benefits from the combined effect of vacuum induced interference effects and coherent effects induced by strong coherent fields. The dependence of the gain of the detection field on the phase difference of the coherent field is due to the combination of these two effects and the establishment of two different but interrelated atomic transition channels. When the excited-state atoms transition downwards through different channels, the emitted photons have different primary phases. Thus, we can control the inter-channel interference results by tuning the phase differences.
Based on the above knowledge, even if the two lower levels of the system are non-degenerate, as long as we manage to make them related (such as coupling with a microwave field), then there are two different channels when the atoms transition from the excited state downwards. Therefore, the enhancement of the non-inversion gain of the detection field and its phase control can still be achieved.
Gain Phase Control of Detection Field Based on Coherently Excited Particle Number Inversion Wu Jinhui, Gao Jinyue (College of Physics, Jilin University, Changchun 130023, China) There are currently two different methods that can be used to obtain laser oscillations. One is the traditional population inversion laser. The other is the non-particle-count reversal laser proposed in the late 1980s.In order to realize the traditional inverted laser oscillation, the irreversible spontaneous radiation process or incoherent pumping process must be used to make the laser transition upper level particle number. It is larger than the number of lower level particles, and when a strong coherent field acts on an energy level of the laser transition, laser oscillation may occur even if the number of upper level particles is less than the number of lower level particles. .
In this paper, based on the irreversibility of the bi-coherent field excitation, we discuss the possibility of realizing a completely new laser oscillation in a /1 type three-level atom system with near degenerate energy levels. Since the two lower energy levels of the atomic system are nearly degenerate, we must consider the existence of interference effects induced by the vacuum electromagnetic field. Of course, the precondition for this kind of interference effect is that the corresponding dipole matrix elements must be non-orthogonal. Two strong coherent fields act on two different dipole allowable transitions, respectively.
With the dipole approximation and rotation wave approximation, we obtain the analytical solution of the particle number distribution at each level by solving the density matrix equation in the steady state of the system. From the analytical solution, it is found that the population inversion can be achieved on any transition under the appropriate parameter conditions. Moreover, the inversion of the number of particles is related to the phase difference between the two coherent fields. We can control the degree of inversion by tuning the phase of one field.
In order to examine the gain of another weak detection field, we obtain its gain or absorption coefficient by the Laplace transform method. Through numerical solution mapping, it is found that the inversion of the population based on this full coherent excitation can achieve the detection field gain, and then obtain a new type of laser oscillation. Since there are population inversions in the atomic system, the population inversion is achieved by the irreversibility of the excitation of the coherent field (instead of relying on non-coherent irreversible processes), so this laser is not only different from the non-inverse. Turning the laser is also different from the traditional reverse laser. Due to the presence of vacuum-induced interference effects, we can also control the detection field gain by tuning the coherent field phase, which is different from the traditional method of controlling the detection field gain by tuning the amplitude or frequency of the coherent field.
The non-orthogonality of the corresponding dipole matrix elements can be achieved by mixing between the low energy levels. The mixing of energy levels can be based on the infield length of the atomic system or the addition of a microwave field.
Femtosecond Laser Transmission in Quartz Glass Gong Qihuang, Wu Chaoxin, Luo Le, Sun Quan, Yang Hong, Jiang Hongbing (College of Physics, Peking University, Beijing 100871, China) The transmission of femtosecond laser pulses in transparent media is a hot topic in recent years. The long filament effect of the femtosecond pulse in the air has attracted wide attention, and the nonlinear transmission of the femtosecond intense light pulse in air has been studied in depth.The femtosecond pulse is nonlinear in the transparent solid medium. The transmission is more complicated, but the research is still relatively small.We have made detailed studies on the transmission of femtosecond intense light pulses in quartz glass.
A titanium sapphire laser is used to amplify 800 urn, 120 fs laser pulses. After the hole filtering, the microscope objective focuses on the body or surface of the quartz sample.
First, we studied the filament formation and refocusing in quartz glass under different focusing parameters for femtosecond laser pulses. We have found that if we use low numerical aperture (Han 4) to further understand the kinetics of femtosecond laser pulse transmission in the quartz glass, we studied the lateral distribution of the light field and spectral changes during filament formation. The defocusing effect of the optical field formed by the annular structure, super-Miss distribution and self-limitation, as well as the accompanying spectral broadening of the laser.
Theoretically, we start with the nonlinear Schrodinger equation describing the transmission of femtosecond laser pulses, obtain a semi-analytical solution under the approximate conditions that the Gaussian distribution and the time domain distribution remain unchanged in the lateral direction, and qualitatively explain the filaments of multiple focal points. The relationship between phenomena and focusing parameters. Further, we numerically simulated the nonlinear Schrödinger equation and analyzed the longitudinal filamentation, refocusing, and transverse light field during femtosecond laser transmission. The kinetics of the femtosecond laser pulse transmission in the quartz glass was relatively clear. To understanding.
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