Laser-sustained plasma light source plays an important role in industrial production, especially in semiconductor inspection because of its high brightness, long lifetime and high stability. The plasma temperature is an important index to characterize the brightness and spectral composition of the light source. The higher the plasma temperature is, the higher the brightness of the light source is, and the more ultraviolet spectrum components are in the light source. Therefore, the analysis of the plasma temperature can guide the optimization design of the laser-sustained light source. In this paper, simulation model is bult using Comsol Multiphysics software and completed by using heat transfer module, mathematics module and fluid module. The influence of interior flow field of the high-pressure bulb on plasma temperature is considered. The analysis results show that under the existing high pressure bulb structure, irregular flow field will be formed due to thermal effect, resulting lower plasma temperature and affecting the stable output of the light source. By adding the gas flow device and controlling the gas flow rate, the irregular flow field can be reduced, and higher plasma temperature is obtained, which means the brightness of the light source can be improved.
The thermal focal length of the side-pumped module was first measured at different pump currents, revealing a relationship between thermal focal length and pump current. Then, a linear resonant cavity was designed and optimized. A 1064 nm pulsed laser was generated by using LD side-pumped Nd:YAG laser and acousto-optic(AO) Q-switching technology. BBO and LBO crystals were utilized for second-harmonic generation (SHG) and sum-frequency generation (SFG), respectively. At a repetition rate of 8 kHz, the maximum average power of the 355 nm ultraviolet (UV) output reached 2.13 W, with a pulse width of 32.7 ns. The optical-to-optical conversion efficiency from 1064 nm to 355 nm was 24.3%. At last an analysis was conducted on the impact of the 1064nm to 532 nm photon number ratio's impact on SFG, and the optimal power ratio is close to 1:2 for achieving high conversion efficiency of 355 nm laser output.
A compact dual wavelength Nd:YVO4/MgO:PPLN infrared laser was developed successfully which was composed of Nd:YVO4 crystal, MgO:PPLN crystal and a cavity mirror(M1). The fundamental laser was consisted of the first face of Nd:YVO4 and M1, and the optical parametric oscillation(OPO) cavity defined by the second face of Nd:YVO4 and M1. The infrared laser output with wavelengths of 1539 nm and 3447 nm was obtained using intracavity cw OPO technology. The output power of 1539nm and 3447nm were 670mW and 236mW at the pumped LD power of 6.0 W, and the optical conversion efficiency was 15.1%. The higher conversion efficiency was mainly attributed the 2mm thickness of MgO:PPLN crystal. Intracavity dual wavelength laser can be used in spectrum detection, drunk driving test and so on.
This system uses SOI optical waveguide ring resonator chip. By using the method of selecting single direction light path, we got the resonance curve and backscattering curve of the resonant, while the system is working under different light powers. The changing rules of FWHM and resonant depth under different light powers is analyzed. And the action mechanism of optical power on the cavity resonance curve and backscattering is analyzed. Finally, the optimal working optical power of SOI integrated optical gyroscope system is determined.
Based on the asymmetric directional coupler, a polarization beam splitter based on silicon on Insulator (SOI) platform is designed for the wavelength range of 1500nm-1600nm in optical communication in this letter. The asymmetric directional coupler is composed of a regular strip shape waveguide and a sub-wavelength grating waveguide. The influence of the grating period, grating depth, and duty cycle on its polarization characteristics is analyzed. The simulation results show that the polarization extinction ratio (PER) of TE polarization is 20-23 dB and the insertion loss (IL) is 0.01-0.04dB, in the wavelength range of 1500–1600nm, while the PER of TM polarization is 15-26 dB and the IL is 0.3-0.6dB. Especially, the PER and IL are 21 dB (26 dB) and 0.31 dB (0.26 dB) for TE (TM) at the wavelength of 1550 nm. Moreover, the minimum feature size of this device is 25 μm2 . It can be effectively used in semiconductor photoelectronic devices.
Alexandrite crystal is a broadband tunable gain medium with good performance in near infrared band. At room temperature, the wavelength tuning range of the alexandrite laser is about 700~818nm, UV or deep-UV (DUV) lasers can be obtained by single or multiple optical nonlinear frequency conversions. The laser oscillations can be generated when alexandrite crystals absorb pumping light energy, and a considerable part of pumping energy will be converted into thermal energy of crystals which will lead to a thermal effect. It will affect the output laser efficiency, the stability of resonator and the quality of output laser beam. In this paper, by establishing the thermal conduction model of the crystal, the stable temperature field distribution, deformation field distribution, and thermal stress field distribution in the crystal can be obtained by solving the corresponding equations. Then the thermal effects caused by these three fields are analyzed respectively, and the corresponding focal lengths of thermal are calculated which shows an inverse relationship between the focal length of the thermal and the absorption pumping power when other conditions remain unchanged. The stable parameter range of the laser cavity can be obtained according to the stable conditions of the resonator, and it will play a guiding role in solving the thermal effect of the crystal and improving the performance of the laser.
Taper is a basic device widely used in photonics technology which transmits light between the waveguides with different widths. Tapers are usually designed to be trapezoidal in shape, which is simple but has many limits. If the taper is designed to be too short, the broken lines at the junction positions between the strip waveguides (SWGs) and the taper will excite high-order modes and cause high fundamental mode loss. As a result, the traditional tapers are always with a long length which limits the miniaturization of photonic systems. To solve this problem, we proposed a method based on forth-order Bezier curve that made the taper has both small size and good performances on the transmission loss of fundamental mode and the mode excitation ratios (MERs) of high-order modes. According to the obtained results, the proposed Bezier curve method decreased the length of a taper from 100μm to 30μm on the premise of maintaining the performances.
A novel ultralow loss bent waveguide for single-mode operation was designed based on the Euler spiral. The proposed 180° bend (U-bend) was composed of two identical 90° Euler bends with gradient width from 1.6μm to 0.45μm and a 0.45μm wide, 2μm long strip waveguide. The proposed U-bend had ultralow losses (<−0.0005dB) and very low mode excitation ratios (MERs) of high-order modes (<−35dB) over a broad wavelength-band by lumerical simulation software. The effective radius Reff of the designed U-bend was as small as 42.547μm and the transmission ratio of fundamental-mode was 0.99988 that almost equal to 1. After simulation and computation, only the fundamental-mode could be retained and propagated in the designed U-bend waveguide with ultralow loss.
All-solid-state (ASS) ultraviolet (UV) laser is an organic combination of ASS laser technique and nonlinear frequency conversion technique. By using different kinds of nonlinear optical crystals and optimizing the system structure, the conversion efficiency and output power of fifth-harmonic-generation (5HG) of ASS lasers has been constantly updated. And the expected UV laser with high beam quality and stability was obtained through reasonable system design. In this paper, the research status of 5HG for ~1 μm near-infrared ASS lasers were briefly reviewed, different approaches for producing 5HG were compared, and the advantages and disadvantages of the corresponding approaches are analyzed.
KEYWORDS: Holograms, Holography, 3D image reconstruction, Near field diffraction, 3D displays, Fourier transforms, 3D image processing, Tomography, Diffraction, Reconstruction algorithms
A rapid algorithm of multi-plane holographic display is given. A proper thin lens phase factor was combined with fast Fourier transform (FFT) in this algorithm to move the reconstructed image of Fourier transform hologram to specify depth from infinity and the imaging effect of this algorithm is identical with Fresnel diffraction. Using this simple operation replaced complicated Fresnel diffraction integral in the Ping-Pong iteration algorithm, the computational load of multi-plane hologram was reduced and computational speed was significantly increased. Moreover, the hologram of a 3-D object consists of two pictures at different depths was computed by this modified Ping-Pong algorithm. The reconstructing of this obtained hologram was also simulated in MATLAB. The result showed the new algorithm is feasible and effective.
A multi-wavelength mid-infrared laser based on a multi-period doped MgO periodically poled lithium niobate (MgO:PPLN) was reported in this letter. The pump source was 1.064μm Q-switched Nd:YVO4 laser with a pulse repetition rate of 15kHz and pulse duration around 30ns. Three domain periods of 28.5μm, 29μm and 29.5μm in series were fabricated in a 2mm-thick z-cut MgO:PPLN, and the length of each domain period was 20mm. The extra-cavity singly resonant optical parametric oscillator had been demonstrated with a compact two-mirror cavity. Three idler wavelengths of 3825nm, 4004nm and 4165nm in the mid infrared were obtained at the same time, and the total output power was 139mW at 1.064μm pump power of 3.09W corresponding to optical-to-optical conversion efficiency of 4.5% and the pump threshold was 1.04W for the 60mm-long MgO:PPLN.
Compact and efficient blue laser sheet has important applications in the field of measurement, with laser diode end pumped Nd:YAG directly and LBO intracavity frequency doubling, a compact and efficient CW 473nm blue laser sheet composed of dual path liner blue laser is realized. At an incident pump power of 12.4W, up to 1.4W output power of the compound blue laser is achieved, the optical-to-optical conversion efficiency is as high as 11.3%.
With diode end pumped Nd:YAG directly and LBO intracavity frequency doubling, a compact, high efficient continuous wave blue laser at 473nm is realized. When the incident pump power reach 6.2W, 630mW maximum output power of blue laser at 473nm is achieved with 15mm long LBO, the optical-to-optical conversion efficiency is as high as 10.2%.
Compact, high power, and low-cost green laser light sources are needed in projection-related applications such as digital cinema, rear-projection television, simulators, and command and control stations. We report a LD array directly pumped intracavity SHG Nd:YVO4/PPMgLN laser without lens or waveguide in this letter. A compact 3.12 W green laser was demonstrated by intra-cavity frequency doubled using a PPMgLN bulk crystal by a 19-emitter LD array pumped(single bar), the conversion efficiency from input LD array was 9.2%. A line-beam output suitable for laser projectors was generated, which has the potential to be scalable to small volumes and low costs for laser projection displays.
We described a widely tunable intracavity continuous-wave singly resonant optical parametric oscillator (SRO) through a minimal laser diode end-pumped Nd:YVO4 laser. Laser source from 1.9μm to 2.4μm is obtained by temperature tuning of the 32.2μm period periodically poled MgO:LiNbO3(PPMgLN) crystal. The maximum power, 0.84W signal wave at 1.966μm and 0.56W idler wave at 2.319μm, are simultaneously obtained at 5.5 W of input diode power. The corresponding conversion efficiency are 15.2% and 10.2% respectively, so the whole efficiency is more than 25%. This allows the development of practical infrared cw SRO’s using compact, widely available, low-cost laser pump sources.
With diode end pumped Nd:YVO4 and PPMgLN intracavity sum-frequency mixing, a compact, high efficient continuous wave yellow laser at 593.5nm is realized. At an incident pump power of 5.7W, up to 620 mW output power of yellow laser is achieved, the optical-to-optical conversion efficiency is as high as 10.9%.
High power green laser has many applications such as high brightness laser projection and large screen laser theater. A compact and high power green-light source has been developed in diode-pumped solid-state laser based on MgO doped periodically poled LiNbO3 (MgO:PPLN). 5W fiber coupled green laser is achieved by dual path Nd:YVO4/MgO:PPLN intra-cacity frequency-doubled. Single green laser maximum power 2.8W at 532nm is obtained by a 5.5W LD pumped, MgO:PPLN dimensions is 5mm(width)×1mm(thickness)×2mm(length), and the optical to optical conversion efficiency is 51%. The second LD series connected with the one LD, the second path green laser is obtained using the same method.
Then the second path light overlap with the first path by the reflection mirrors, then couple into the fiber with a focus mirror. Dual of LD, Nd:YVO4, MgO:PPLN are placed on the same heat sink using a TEC cooling, the operating temperature bandwidth is about 12°C and the stablity is 5% in 96h. A 50×50×17mm3 laser module which generated continuous-wave 5 W green light with high efficiency and width temperature range is demonstrated.
High efficient and compact continuous-wave arrayed green laser is demonstrated based on periodically poled MgO:LiNbO3(PPMgLN), with a pump power of 16.5 W (5.5 W×3) at 808 nm, 7.36W output power of 3-arrayed green beams at 532 nm is achieved with a high optical-to-optical conversion efficiency of 44.6%.
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