Zigzag Slab Research Articles

Innozag amplifier: optimizing the Innoslab platform to improve beam quality and gain

This study presents an innovative zigzag-type Innoslab amplifier platform, termed ‘Innozag,’ that merges the essential attributes of both Innoslab and zigzag slab amplifiers. A thorough theoretical and experimental examination has been performed to analyze and compare the gain and amplified beam wavefront distortion of the Innoslab and Innozag amplifiers. Our investigation includes detailed optical path difference computation coupled with examination of the far-field amplified beam profile. The results confirm that the Innozag amplifier reduces the thermally induced wave distortion by up to 40%. Geometric features, particularly the overlapping zones in the zigzag path, increase the gain of the Innozag amplifier. The Innozag design achieves an amplification factor 1.4 times greater than that of the Innoslab amplifier in a five-pass structure.

500 Hz Joule-level output by sub-nanosecond Zig-Zag slab laser

500 Hz Joule-level output by sub-nanosecond Zig-Zag slab laser

High-power CW 1048 nm Yb:YAG Dual-Ended Diode-pumped zigzag slab Laser

We developed a high-power continuous-wave (CW) 1048 nm Yb:YAG laser oscillator with a folded cavity structure. Based on a surface gain slab structure of Yb:YAG, the CW laser output property of 1030 and 1048 nm wavelengths is theoretically analyzed. In order to achieve a CW single-wavelength laser output at 1048 nm, a high-power pump and the suppression of laser oscillations at other wavelengths were required. In our experiments at 4200 W of pump power, we obtained a maximum output power of 1330 W, with an optical–optical conversion efficiency of 31 %, a maximum slope efficiency of 46.4 % and a beam quality (β) of 1.7 times the diffraction limit. We also proposed a laser oscillator. To the best of our knowledge, we obtained the highest power and beam quality for Yb:YAG laser oscillators at 1048 nm. This work could provide a useful platform for developing 1048 nm lasers with higher power and beam quality and increasing the accessibility of the 1048 nm regime.

Amplification of high repetition-rate, picosecond laser pulses using a zig-zag slab configuration

Laser sources which generate high peak-pulse energy, picosecond pulse duration outputs at high repetition rates are of particular interest for applications including laser ignition and space fragment detection. In this work, we demonstrate the design and operation of a zig-zag slab, solid-state master oscillator power amplifier (MOPA) which yields high energy amplification. The system uses a weakly-doped Nd:YAG slab as the amplifier medium, to amplify laser pulses from a passively Q-switched microchip seed laser. The seed laser beam undergoes four passes of the slab amplifier resulting in an amplified output pulse with hundreds of picoseconds pulse duration. We investigate the relationship between the angle of incidence of the seed laser beam into the amplifier slab and its effect on the slab fill-factor and overall laser field amplification. We also investigate the impact that the temperature of the laser diode array (LDA) which is used to pump the slab amplifier, has on the amplification efficiency of the MOPA. Experimentally, we demonstrate an amplification factor of ∼90 times from the optimized slab amplifier, and a resultant output laser field with a pulse energy of 99.58 mJ, a pulse duration of 491 ps, and a repetition rate of 200 Hz. We believe that this work will pave the way towards the development of novel all-solid-state amplifier designs for the generation of high-energy, high repetition frequency, sub-nanosecond laser outputs.

Theoretical study on beam quality and thermal stability in solid-state zigzag tube laser amplifier

Compared to zig-zag solid-state slab lasers, zig-zag solid-state tube lasers (SSZTLs) exhibit significant potential in beam quality improvement and output power enhancement. However, the progress of SSZTLs still faces enormous challenges due to the lack of effective control of beam quality. We first developed a comprehensive model for analyzing the output beam quality of zig-zag tube lasers by taking both the fabrication and alignment errors and thermal effects into consideration. The primary factors degrading the beam quality and thermal stability of the SSZTLs were analyzed in detail, and a self-correction method based on the complementary optical path was further proposed and analyzed theoretically to effectively improve the beam quality and thermal stability of the SSZTLs. The results show that this method can not only effectively correct the off-axis aberrations but also mitigate the depolarization loss that arises from the thermal instability of the SSZTLs. This work can provide a reference in the beam control and applications of SSZTLs.

A 117-W 1.66-Times Diffraction Limited Continuous-Wave Nd:YVO4 Zigzag Slab Laser with Multilayer Amplified-Spontaneous-Emission Absorbing Coatings**Supported by the National Key R&D of China (Grant No. 2016YFB0402103), the National Natural Science Foundation of China (Grant No. 61875208), and the Knowledge Innovation Program of Chinese Academy of Sciences (Grant No. GJJSTD20180004).

We report a continuous-wave end-pumped Nd:YVO4 zigzag slab laser with multilayer amplified spontaneous emission (ASE) absorbing coatings. The coatings are deposited on the slab faces. A five-layer structure consists of SiO2-Ti-SiO2-Ti-Au, and the thicknesses are 2520 nm, 10 nm, 160 nm, 24 nm and 200 nm, respectively. The designed coatings show good performance for the ASE control in the experimental tests. A stable-unstable hybrid laser oscillator along orthogonal directions in the slab aperture is further configured, achieving the 117W output at a pump of 328 W. The beam quality factors M2 in the unstable direction and stable direction are 1.57 and 1.66, respectively.

An especial configuration for an Nd:YAG end-pumped zigzag slab gain module based on crystalline polytetrafluoroethylene and a specific optical system for pump-beam delivery.

This work experimentally introduces a new single-crystal Nd:YAG end-pumped zigzag slab (EPZS) gain module based on a thin polytetrafluoroethylene (PTFE) sheet as a total internal reflection (TIR) protection layer. In this gain module, a specific optical pump-beam delivery (OPBD) system is used to improve the output beam quality (BQ) of the slab amplifier from 9.4 in a typical OPBD system to 4.7 with the total pump power of 2400 W. The average logarithmic small-signal gain (g0l) in the 0.06% Nd:YAG EPZS gain module at the laser beam incident angle of 7.1° was obtained around 0.64 for the two OPBD systems mentioned above.

Theoretical and experimental investigation of injection seeded Nd:YAG zigzag slab ring lasers

A comprehensive theoretical and experimental investigation of injection seeded Nd:YAG zigzag slab ring lasers is presented. The effects of injected intensity and detuning frequency on the dynamic process of mode competition are analyzed. A stable single frequency injection seeded Nd:YAG zigzag slab ring oscillator has been built by using the ramp-fire technique with a RbTiOPO4 phase modulator. A linear ramp voltage is used and the detuning frequency is precisely controlled by firing the Q-switch with an adjustable delay time after the resonance condition. Both the simulation and the experiments carried out at various injection conditions have demonstrated that the spectral purity of the output pulse increases with the increase of injected intensity and with the decrease of detuning frequency, and that the frequency locking range increases for both high injected intensity and high gain. The experimental measurements of output pulse energy and pulse width are also in good agreement with the theoretical results.

Frequency stabilization of an injection seeded Nd:YAG ring oscillator by ramp-fire technique with a RbTiOPO4 modulator

We report on an injection seeded Q-switched Nd:YAG zigzag slab ring oscillator with pulse energy of 67 mJ and pulse duration of 19 ns at repetition rate of 20 Hz. With a RbTiOPO4 (RTP) electro-optic crystal as the intra-cavity phase modulator, stable single frequency operation is achieved using the ramp-fire technique with a 10 µs linear voltage ramp sweeping 2.5 free spectral ranges. Frequency jitter of output pulse at 1064 nm is measured to be 2.0 MHz over 7 min. The beam quality factor is $$ M_{x}^{2} = 1.38 \pm 0.03, M_{y}^{2} = 1.29 \pm 0.02 $$ in seeded operation, which is improved from that of $$ M_{x}^{2} = 1.67 \pm 0.01, M_{y}^{2} = 1.35 \pm 0.01 $$ in free oscillation. The measured linewidth of the output is 27 MHz, which is 1.2 times Fourier-transformed-limited. Based on the RTP crystal as the modulator, the ramp-fire technique with a high ramp speed is capable of achieving high frequency and timing stability.

Narrow-linewidth, quasi-continuous-wave ASE source based on a multiple-pass Nd:YAG zigzag slab amplifier configuration.

We present investigations into a narrow-linewidth, quasi-continuous-wave pulsed all-solid-state amplified spontaneous emission (ASE) source by use of a novel multiple-pass zigzag slab amplifier. The SE fluorescence emitted from a Nd:YAG slab active medium acts as the seed and is amplified back and forth 8 times through the same slab. Thanks to the angular multiplexing nature of the zigzag slab, high-intensity 1064-nm ASE output can be produced without unwanted self-lasing in this configuration. Experimentally, the output energy, optical conversion efficiency, pulse dynamics, spectral property, and beam quality of the ASE source are studied when the Nd:YAG slab end-pumped by two high-brightness laser diode arrays. The maximum single pulse energy of 347 mJ is generated with an optical efficiency of ~5.9% and a beam quality of 3.5/17 in the thickness/width direction of the slab. As expected, smooth pulses without relaxing spikes and continuous spectra are achieved. Moreover, the spectral width of the ASE source narrows versus the pump energy, getting a 3-dB linewidth of as narrow as 20 pm (i.e. 5.3 GHz). Via the sum frequency generation, high-intensity, smooth-pulse, and narrow-linewidth ASE sources are preferred for solving the major problem of saturation of the mesospheric sodium atoms and can create a much brighter sodium guide star to meet the needs of adaptive imaging applications in astronomy.

Interface and material engineering for zigzag slab lasers

Laser damage of zigzag slab lasers occurs at interface between laser crystal and SiO2 film. Although an additional HfO2 layer could be used to manipulate electric-field on the crystal-film interface, their high absorption and polycrystalline structure were unacceptable. SiO2 was then doped in HfO2 to suppress its crystallization and to achieve low absorption by annealing. HfxSi1−xO2 nanocomposite layers were then inserted between laser crystal and SiO2 film to minimize electric-field at crystal-film interface. Laser damage resistance of this new architecture is two times higher than that of traditional zigzag slab lasers.

High Power Continuous Wave Yb:YAG Composite Crystal Zigzag Slab Amplifier at Room Temperature

A 7.07-kW Yb:YAG composite crystal zigzag slab amplifier at room temperature is developed and demonstrated, the optical-to-optical efficiency is about 29.5% and the slope efficiency is 39.5%, respectively, with the pumping power of 19.98 kW and the incident seed laser power of 1.18 kW. The influence of the pump coupling efficiency, the intensity of the seed laser, and the temperature to the extracted power from the Yb:YAG slab are analyzed by simulation. The fluorescence distribution at the end face and the transmission wavefront of the Yb:YAG slab are measured, the nonuniformity of the fluorescence distribution is less than 6%, and the P-V value of the transmission wave front distortion is less than 1.6 μm.

Direction-dependent waist-shift-difference of Gaussian beam in a multiple-pass zigzag slab amplifier and geometrical optics compensation method.

Zigzag and non-zigzag beam waist shifts in a multiple-pass zigzag slab amplifier are investigated based on the propagation of a Gaussian beam. Different incident angles in the zigzag and non-zigzag planes would introduce a direction-dependent waist-shift-difference, which distorts the beam quality in both the near- and far-fields. The theoretical model and analytical expressions of this phenomenon are presented, and intensity distributions in the two orthogonal planes are simulated and compared. A geometrical optics compensation method by a beam with 90° rotation is proposed, which not only could correct the direction-dependent waist-shift-difference but also possibly average the traditional thermally induced wavefront-distortion-difference between the horizontal and vertical beam directions.

Wavefront improvement in an end-pumped high-power Nd:YAG zigzag slab laser.

Techniques for wavefront improvement in an end-pumped Nd:YAG zigzag slab laser amplifier were proposed and demonstrated experimentally. First, a study on the contact materials was conducted to improve the heat transfer between the slab and cooling blocks and to increase the cooling uniformity. Among many attempts, only the use of silicon oil showed an improvement in the wavefront. Thus, the appropriate silicone oil was applied to the amplifier as a contact material. In addition, the wavefront compensation method using a glass rod array was also applied to the amplifier. A very low wavefront distortion was obtained through the use of a silicone-oil contact and glass rod array. The variance of the optical path difference for the entire beam height was 3.87 μm at a pump power of 10.6 kW, and that for the 80% section was 1.69 μm. The output power from the oscillator was 3.88 kW, which means the maximum output extracted from the amplifier at a pump power of 10.6 kW.

Automatic low-order aberrations compensator for a conduction-cooled end-pumped solid-state zigzag slab laser

In order to solve the problem of large low-order aberrations with solid-state zigzag slab lasers, an automatic compensator has been developed in this paper. In this compensator, three lenses are mounted on a motorized rail, whose positions can be obtained using ray tracing method based on the beam parameters detected by a wave-front sensor. The initial peak to valley (PV) values of the wave-front range up to several tens of microns. Both simulated and experimental results show that the PV values of the wave-front can be reduced to around 1.6μm with the proposed automatic compensator.

Compact, high-power, high-beam-quality quasi-CW microsecond five-pass zigzag slab 1319 nm amplifier

We demonstrate a compact, high-power, quasi-continuous-wave (QCW) end-pumped 1319 nm Nd:YAG slab amplifier laser with good beam quality. The laser is based on a QCW pulse Nd:YAG master oscillator and Nd:YAG slab amplifier with multi-pass zigzag architecture. The amplifier operates at a pulse repetition frequency of 500 Hz and pulse width of ∼105 μs, delivering a maximum output power of 51.5 W under absorbed pump power of 217.8 W and corresponding to an extraction efficiency of 14.2%. The beam quality factor is measured to be Mx2=1.61 and My2=1.81 in the orthogonal directions. To the best of our knowledge, this is the first compact, high-power, high-beam-quality QCW Nd:YAG amplifier at 1319 nm based on a multi-pass zigzag slab structure.

Quasi-continuous-wave, laser-diode-end-pumped Yb:YAG zigzag slab oscillator with high brightness at room temperature

An experimental demonstration of a quasi-continuous-wave, laser-diode (LD)-end-pumped Yb:YAG zigzag slab oscillator with a high efficiency and power at room temperature has been presented. An image-inverting resonator was used in the slab laser to avoid beam excursion to the slab end and laser power instability. The emitted laser had an average power of 330 W at 1030 nm when the average pump power was 712 W at 940 nm with a repetition rate of 10 Hz and a pulse duration of 10 ms, which corresponded to an optical conversion efficiency of 46.3% and a slope efficiency of 56.0%.

Design of pump beam delivering optical system and doped YAG length to minimize the wavefront distortion in a high-power Nd:YAG zigzag slab laser

An end-pumped high-power Nd:YAG zigzag slab continuous wave laser amplifier was designed through a computational simulation to minimize the wavefront distortion of the output laser beam. The pump beam delivering optical system was optimized with an acylindrical slow-axis lens to lower the distortion of nonzigzag propagation for the beam height axis. In addition, the wavefront distortion of the zigzag propagation for the beam width axis was studied and minimized by slightly changing the doped YAG length. The simulation results of the final design showed a peak-to-valley optical phase difference (OPDP−V) of 0.83 μm and a very low beam quality of 1.19× diffraction limit, even with a total pump power of 10 kW.

High-efficiency, high-average-power, CW Yb:YAG zigzag slab master oscillator power amplifier at room temperature.

We demonstrate a high-efficiency, high-average-power, CW master oscillator power amplifier based on a conduction-cooled, end-pumped Yb:YAG slab architecture at room temperature (RT). Firstly, the CW amplification property is theoretically analyzed based on the kinetics model for Yb:YAG. To realize high-efficiency laser amplification extraction for RT Yb:YAG, not only intense pump but also a high-power seed laser is of great importance. Experimentally, a composite Yb:YAG crystal slab with three doped and two un-doped segments symmetrically is employed as the gain medium, which is end-pumped by two high-power, 940-nm diode lasers. A high-power, narrow-spectral-width, 1030-nm fiber seed laser then double passes the composite slab to realize efficient power amplification. For 0.8-kW seed input, maximum output power of 3.54 kW is obtained at 6.7 kW of pump power, with the optical conversion efficiency of 41% and the highest slope efficiency of 59%. To the best of our knowledge, this is the highest power and efficiency reported for Yb:YAG lasing at RT except thin-disk lasers.

Simulation of the wavefront distortion and beam quality for a high-power zigzag slab laser

A simulation method of the beam quality for a high-power zigzag slab laser has been developed. This method can predict the wavefront distortion and beam quality for various optical arrangements and optimize the design effectively. A Nd:YAG zigzag slab laser amplifier was designed as an application. The optimized design shows a beam quality of 1.20 corresponding to the minimized wavefront distortion with a peak-to-valley of 0.568μm and root mean square of 0.115μm even under high-power operation with a total pump power of 14kW. Although there are some effects other than the optical design error that incur wavefront distortions, this method can help to determine the first optical design of the zigzag slab laser without the need for many experimental studies.