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1.
We have measured the effect on laser beam quality factorM
2 of spherical aberration in a simple planoconvex lens. Theory predicts that the laser beam quality should remain essentially unchanged until the incident beam widthw exceeds a critical widthw
q above which the beam quality will degrade rapidly, with theM
2 value increasing as (w/w
q
4). We find good agreement between this theory and our experimental data. 相似文献
2.
Propagation of the off-axis superposition of partially coherent beams through atmospheric turbulence
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The propagation properties of the off-axis superposition of
partially coherent beams through atmospheric turbulence and their
beam quality in terms of the mean-squared beam width w(z) and the
power in the bucket (PIB) are studied in detail, where the effects
of partial coherence, off-axis beam superposition and atmospheric
turbulence are considered. The analytical expressions for the
intensity, the beam width and the PIB are derived, and illustrative
examples are given numerically. It is shown that the maximum
intensity Imax and the PIB decrease and w(z) increases as
the refraction index structure constant Cn2 increases.
Therefore, the turbulence results in a degradation of the beam
quality. However, the resulting partially coherent beam with a
smaller value of spatial correlation parameter γ and larger
values of separate distance xd and beam number M is less
affected by the turbulence than that with a larger value of γ
and smaller values of xd and M. The main results obtained
in this paper are explained physically. 相似文献
3.
Thermal lensing has been studied by a probe beam technique in flashlamp-pumped Nd:KGdW laser rods with rod axes positioned
in the N
p–N
g plane and making different angles with the N
g optical indicatrix axis. It was found that the orientation of principal meridional planes of the astigmatic thermal lens
in Nd:KGdW corresponds to the directions with maximum and minimum values of thermal-expansion coefficient in the plane perpendicular
to the rod axis. The athermal Nd:KGdW laser crystal orientation defined as orientation with weak positive near spherical thermal
lens has been determined to make an angle of 30○–40○ with the N
g axis for light polarization E∥N
m. 相似文献
4.
A fiber-coupled laser-diode (LD) end-pumped Nd:GdVO4 slab continuous-wave (CW) 912-nm laser and an LD bar end-pumped Nd:GdVO4 slab CW 912-nm laser are both demonstrated in this paper. Using the fiber-coupled LD of end-pumped type, a highest CW 912-nm laser output power of 10.17 W is obtained with a high optical-to-optical conversion efficiency of 24.6% and a slope efficiency of 34.5%. The measured M2 factors of beam quality in x and y directions are 5.3 and 5.1, respectively. Besides, an LD bar of end-pumped type is used to realize CW 912-nm laser output, which has the advantages of compactness and low cost. When the pump power is 38.8 W, the output power is 8.87 W and the measured M2 factors of beam quality in x and y directions are 16 and 1.31, respectively. In order to improve the beam quality of the 912-nm laser at x direction, a new quasi-concentric laser resonator will be designed, and an LD bar end-pumped Nd:GdVO4 slab high-power CW 912-nm TEM00 laser will be realized in the future. 相似文献
5.
A simple method to determine the thermal focal length of LD end-pumped solid-state laser with stable resonator is presented. The M2 factor describing the quality of the beam can be obtained by scanning a slit through the multi-mode Gaussian beam field. The waist width of the beam and the corresponding TEM00 under the same parameters of laser are then deduced through the law of multi-mode Gaussian beam propagation. Based on the standard matrix theory of stable resonator, the thermal focal length of the gain medium can be easily achieved. To show the application of this approach, the thermal focal length of an LD pumped Nd:YVO4 laser is measured and the experimental results are in agreement with the theoretical prediction. 相似文献
6.
7.
J. Kawanaka Y. Takeuchi A. Yoshida S. J. Pearce R. Yasuhara T. Kawashima H. Kan 《Laser Physics》2010,20(5):1079-1084
A MOPA laser system for high pulse energy and high average power has been developed by using a cryogenic Yb:YAG. In the regenerative
amplifier with our original TRAM architecture, the high pulse energies of 6.5 and 1.5 mJ were obtained at the repetition rate
of 200 Hz and 1 kHz, respectively. An optical efficiency was as high as ηo-o = 9.3% with an excellent beam quality of M
2 < 1.1, which ensured that a cryogenic Yb:YAG TRAM had a high thermal strength. The following four pass power amplifier with
a cryogenic Yb:YAG rod showed 140 mJ at 100 Hz. Both a high optical efficiency of ηo-o = 30% and a high slope efficiency of ηs = 44% showed that an efficient laser operation could be realized for a power amplification with both a high pulse energy
and a high average power by using a cryogenic Yb:YAG. 相似文献
8.
On the basis of the second-order moment of the power density and in the use of the series expansion, the expressions for the beam width, far-field divergence angle and M2 factor of nonparaxial Hermite–Gaussian (H–G) beams are derived and expressed in a sum of the series of the Gamma function. The theoretical results are illustrated with numerical examples. The M2 factor of nonparaxial H–G beams depends not only on the beam order m, but also on the waist-width to wavelength ratio w0/λ. The far-field divergence angles of nonparaxial H–G beams with even and odd orders approach their upper limits θmax=63.435 and 73.898, respectively, which results in M2<1 as w0/λ→0. For the special case of m=0 our results reduce to those of nonparaxial Gaussian beams. Some problems related to the characterization of the nonparaxial beam quality are also discussed. 相似文献
9.
报道了一种基于频率可调谐准高斯太赫兹波束的透射成像系统.研究表明,在这种成像系统中太赫兹波束具有良好的空间分布特性,其波束质量因子M2x=1.15,M2z=1.25,波束传输特性和聚焦特性良好.实验结果反映出成像系统的空间分辨能力与典型太赫兹波长(250μm)相接近.在太赫兹波输出1.0—2.5THz范围内,成像系统信噪比大于1000dB;在1.8THz处,信噪比
关键词:
太赫兹波
太赫兹成像
太赫兹探测 相似文献
10.
11.
355 nm UV laser was obtained with a pulse width of less than 5 ns and a peak power at megawatt level by adopting the 808 nm
pulse laser diode (LD) side-pumped ceramic Nd:YAG and BBO crystal electrooptical Q-switched. The single-pulse energy was measured
to be 24.3 mJ with 4.86 ns pulse width and 5.11 MW peak power at a repetition rate of 1Hz under a 120 A pump current. Using
a volume of beam splitting mirrors, wavelength outputs at 1064, 532, and 355 nm pulse laser was obtained simultaneously with
a respective average output power of 656.6, 357.1, and 260.5 mW, the beam quality factor M
2 are (M
x − 10642 = 5.83, M
y − 10642 = 5.61), (M
x − 5322 = 4.25, M
y − 5322 = 4.08) and (M
x − 3552 = 6.32, M
y − 3552 = 6.15), corresponding to a conversion efficiency at 11% from 1064 to 355 nm. 相似文献
12.
M.H. Mahdieh 《Optics Communications》2008,281(13):3395-3402
In this paper, propagation of a Gaussian laser beam through turbulent atmosphere is evaluated numerically. The beam quality factor for the propagated beam has been estimated for different turbulent conditions that are characterized by parameter Cn. The calculations show that the beam quality can be affected dramatically by atmospheric turbulence and the laser beam size and wavelength have major role in the results. Furthermore, the propagation of laser beam in longer distance results in more spatial perturbation of the beam. The results of these calculations and evaluation of beam quality factor M2 can be used for estimating the refractive index structure parameter (or atmosphere turbulent parameter) Cn. 相似文献
13.
We report a high power zigzag slab laser oscillator employing two composite Nd:YAG/YAG slab in the cavity. The CW laser output
with the power of 401 W was achieved from the oscillator with the optical-optical efficiency of 32.6%. The beam quality is
estimated as M
x
2 ≈ 10, M
y
2 ∼ 50 in the slab width and thickness direction, respectively. 相似文献
14.
以厄米-双曲余弦-高斯(H-ChG)光束为例,对H-ChG光束通过大气湍流传输时的束宽扩展和角扩展做了详细研究.用相对束宽和相对角扩展代替束宽和角扩展来研究湍流对光束影响的灵敏程度.研究表明,折射率结构常数C2n越小,光束束宽扩展和角扩展越小.有较大阶数m,n,较小参数Ω0和束腰宽度w0 H-ChG光束的角扩展受湍流影响较小.当传输距离足够远时,这一结论对H-ChG光束的束宽扩展也成立.当传输距离不长时,对H-ChG光束相对束宽随Ω0和w0的变化规律做了分析.用数值计算例做了说明,并对结果的正确性做了物理解释.厄米-高斯,双曲余弦高斯和高斯光束在大气湍流中的扩展可作为H-ChG光束的特例来处理.
关键词:
束宽扩展和角扩展
大气湍流
厄米-双曲余弦-高斯光束 相似文献
15.
Based on the second-order moments of partially coherent beams in atmospheric turbulence, the analytical beam propagation factor
of a partially coherent Lorentz–Gauss beam in a turbulent atmosphere is derived. As a special case of the general formula,
the beam propagation factor of a partially coherent Lorentz beam in a turbulent atmosphere is also presented. By using the
derived analytical expression, the beam propagation factor is illustrated and analyzed with numerical examples, and the influences
of the beam parameters a
j
and w
0j
, the coherent parameter τ
j
, the axial propagation distance z, the structure constant Cn2C_{n}^{2}, and the inner scale turbulence l
0 on the beam propagation factor are also discussed in detail. 相似文献
16.
Two flashlamp pumped dye lasers of very high spectral quality are mixed in a LiIO3 crystal to generate a tunable infrared beam through the difference frequency mixing. Thanks to the injection-locking process of the pulsed dye lasers leading to a linewidth of 6 MHz with peak powers of about 10 kW, we obtain an IR beam tunable from 3.5 to 5.9 m with a peak power of 40 W and a linewidth of 9 MHz. As an application we present a spectrum of N2O obtained by differential absorption near 1880 cm–1. The lines of thisQ-branch are Doppler limited at the working pressure (102 Pa). 相似文献
17.
18.
The terahertz (THz) frequency radiation production as a result of nonlinear interaction of high intense laser beam with low density ripple in a magnetized plasma has been studied. If the appropriate phase matching conditions are satisfied and the frequency of the ripple is appropriate then this difference frequency can be brought in the THz range. Self focusing (filamentation) of a circularly polarized beam propagating along the direction of static magnetic field in plasma is first investigated within extended‐paraxial ray approximation. The beam gets focused when the initial power of the laser beam is greater than its critical power. Resulting localized beam couples with the pre‐existing density ripple to produce a nonlinear current driving the THz radiation. By changing the strength of the magnetic field, one can enhance or suppress the THz emission. The expressions for the laser beam width parameter, the electric field vector of the THz wave have been obtained. For typical laser beam and plasma parameters with the incident laser intensity ≈ 1014 W/cm2, laser beam radius (r0) = 50 μm, laser frequency (ω0) = 1.8848 × 1014rad/s, electron plasma (low density rippled) wave frequency (ω0) = 1.2848 × 1014 rad/s, plasma density (n0) = 5.025 × 1017cm–3, normalized ripple density amplitude (μ)=0.1, the produced THz emission can be at the level of Giga watt (GW) in power (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
19.
Thin films of Sb, Se and Sb2Se3 are deposited onto glass and irradiated by a cw-Ar+ laser beam. The kinetics of crystallization and oxidation are traced via the time dependence of optical reflectivity and temperature, T, of the irradiated zone. For Sb2Se3, transformations start abruptly when T attains a critical value, T
c, independently of the laser beam power. These T
c values are comparable to the ones observed under furnace annealing conditions. 相似文献
20.
The analytical expression for the propagation of a flattened laser beam array in a turbulent atmosphere is derived based on extended Huygens–Fresnel principle. The influence of beam order and turbulent atmosphere on beam quality is studied. It is revealed that the beam quality of a coherently combined laser beam array with higher order is better than its lower order counterpart when propagating in free-space, weak and medium turbulence (i.e. Cn2<10?13 m?2/3). The beam quality of higher order beam arrays degrades faster as the intensity of turbulence gets stronger. In the case of propagating in strong turbulence, the beam order has no influence on coherently combined beam quality. 相似文献