Injection-seeded Laser Research Articles

Injection-seeded, Q-switched Ho:YAG laser based on alignment-insensitive corner cone reflectors

This paper demonstrates a single-frequency injection-seeded laser with a Q-switched Ho:YAG laser consisting of two corner cube reflectors. As a seed laser, the Ho:YAG NPRO has an available output power of 1.8 W and operates at 2090.6964 nm. The single-frequency pulse energy obtained in the case of injection-seeded is 6.8 mJ, the pulse width is 166 ns, and the Q-switched Ho:YAG laser operates at a repetition rate of 100 Hz. The Ho:YAG single-pass amplifier scales single-frequency energy from 6.8 mJ to 32.3 mJ. The pulsed spectrum has a half-width of 2.84 MHz. The Ho:YAG amplifier has a beam quality of 1.1 and 1.17 in the x and y axes.

Pound-Drever-Hall locking scheme free from Trojan operating points.

The Pound-Drever-Hall (PDH) technique is a popular method for stabilizing the frequency of a laser to a stable optical resonator or, vice versa, the length of a resonator to the frequency of a stable laser. We propose a refinement of the technique yielding an "infinite" dynamic (capture) range so that a resonator is correctly locked to the seed frequency, even after large perturbations. The stable but off-resonant lock points (also called Trojan operating points), present in conventional PDH error signals, are removed by phase modulating the seed laser at a frequency corresponding to half the free spectral range of the resonator. We verify the robustness of our scheme experimentally by realizing an injection-seeded Yb:YAG thin-disk laser. We also give an analytical formulation of the PDH error signal for arbitrary modulation frequencies and discuss the parameter range for which our PDH locking scheme guarantees correct locking. Our scheme is simple as it does not require additional electronics apart from the standard PDH setup and is particularly suited to realize injection-seeded lasers and injection-seeded optical parametric oscillators.

Injection-seeded single-longitudinal-mode Ti:Sapphire laser with no active stabilization.

We report on the first injection-seeded nanosecond Ti:Sapphire laser that demonstrates a stable single-longitudinal-mode operation with no feedback loop for active cavity stabilization. The short cavity generates 6-mJ transform-limited pulses at a wavelength of 807 nm and with a slope efficiency of 43%. An intracavity dispersive prism makes a novel cavity design for injection-seeded lasers and provides pre-selection of the emission wavelength. In support of these experiments, we perform numerical simulations that include extra cavity losses. The simulation results are in good agreement with the outcome of the experiment and reveal the formation scenario of the laser mode.

High-repetition-rate injection-seeded Nd:YVO4 lasers by high-speed intracavity phase modulation.

We demonstrate high-repetition-rate injection-seeded $Q$Q-switched Nd:YVO4 ring lasers operating at 5 and 10 kHz. The frequency of the lasers is stabilized by the fast ramp-fire technique based on a ${{\rm RbTiOPO}_4}$RbTiOPO4 intracavity phase modulator. At 5 kHz, the highest output energy of 1.5 mJ is achieved with a pulse duration of 8.1 ns, a frequency jitter of 1.7 MHz/min, and a linewidth of 71 MHz. The corresponding values at 10 kHz are 0.7 mJ, 12.1 ns, 1.9 MHz/min, and 45 MHz, respectively. The short-term timing stability is 15 ns. The performance of the lasers demonstrates that the high-speed ramp-fire technique with the intracavity phase modulator is especially appropriate to obtain stable Fourier-transform-limited single-frequency operation of high-repetition-rate injection-seeded lasers.

High-repetition-rate single-frequency Ho:YAG MOPA system.

A stable, 2.09μm single-frequency Ho:YAG master oscillator and power amplifier (MOPA) system at a pulse repetition frequency of 1.25kHz is demonstrated. The maximum output energy of the single-frequency injection-seeded laser is 13.76mJ, and the corresponding pulse width is 178.9ns. The seed laser is a continuous-wave Ho:YAG non-planar ring oscillator laser. The half-width of the pulse spectrum is measured to be 2.65MHz by using the heterodyne technique, which is about 1.06 times Fourier transform limited.

高光谱分辨率激光雷达探测大气透过率

A high spectral resolution lidar(HSRL) based on injection-seeded laser and iodine absorption filter has been developed. The basic principle, data processing method and configuration of HSRL were introduced. The HSRL measurement of atmospheric transmission in cloud and dust cases were presented,and compared with the results retrieved by the traditional Fernald method. Due to the nonidentity in physical and optical properties of different aerosols and cloud, the lidar ratio assumed in Fernald method cannot agrees well with the real atmosphere and produces considerable error in atmospheric transmission. Utilizing different spectral width of molecular scattering and particle scattering, the HSRL could separate two kinds of signals with iodine filter. Therefore, HSRL can measure the atmospheric transmission quantitatively without the additional assumption of lidar ratio.

Improvements in filtered Rayleigh scattering measurements using Fabry–Perot etalons for spectral filtering of pulsed, 532-nm Nd:YAG output

In this manuscript, we investigate a new methodology for increasing the spectral purity of the second-harmonic output of an injection-seeded, frequency-doubled, Q-switched Nd:YAG laser operating near 532 nm. Specifically, tunable Fabry–Perot etalons (FPEs) are used as ultra-narrowband spectral filters, transmitting the desired single-mode output, while filtering out a significant portion of the broadband pedestal characteristic of injection-seeded lasers. A specific emphasis is placed on the design and optimization of the FPEs in the context of filtered Rayleigh scattering (FRS) measurements and how their utilization results in substantial increases in spectral purity, realizable attenuation of unwanted scattering, and applications in environments with high particulate levels. Experimental results show an increase in laser spectral purity of more than one order-of-magnitude (from 0.99997 to 0.999998) when using FPE filters, which led to a two-order-of-magnitude increase in achievable attenuation of laser light passing through a molecular iodine filter. The utility of the FPE-based spectral filtering of the pulsed Nd:YAG output for 2D FRS imaging was demonstrated in turbulent, isothermal gas-phase jets, seeded with varying levels of non-evaporating droplets with particle volume fractions (FVp) ranging from ~5 to >60 parts-per-million (ppm). After implementation of an optimized air-spaced FPE in the 532-nm output, no particle scattering was observed (based on visual and statistical analysis), even for the highest seed case (FVp ~ 60 ppm), and the gas-phase Rayleigh–Brillouin signals were collected without interference from the flowfield particulate. The current results suggest that the implementation of properly specified FPEs allows FRS to be applied in environments with high flowfield particulate levels; levels are well beyond what have been suitable for previous FRS measurements.

Implementation of Differential Absorption LIDAR (DIAL) for Molecular Iodine Measurements Using Injection-Seeded Laser

Differential absorption LIDAR (DIAL) is frequently used for atmospheric gas monitoring to detect impurities such as nitrogen dioxide, sulfur dioxide, iodine, and ozone. However, large differences in the on- and off-line laser wavelengths can cause serious errors owing to differential aerosol scattering. To resolve this problem, we have developed a new DIAL system for iodine vapor measurements in particular. The suggested DIAL system uses only one laser under seeded and unseeded conditions. To check the detection-sensitivity and error effects, we compared the results from a system using two seeded lasers with those from a system using a seeded and an unseeded laser. We demonstrate that the iodine concentration sensitivity of our system is improved in comparison to the conventional two seeded or two unseeded laser combinations.

Frequency stabilization of a single-frequency Q-switched Tm:YAG laser by using injection seeding technique

A stable single-frequency Q-switched Tm:YAG laser was demonstrated. The laser was injection seeded by a monolithic nonplanar ring oscillator laser utilizing the ramp-hold-fire technique. The measurements of the output parameters were presented. This paper focused on investigation of the frequency stability of the injection-seeded laser, which was measured by optical heterodyne technique. A method used to restrict the frequency jitter of the laser was discussed. The fluctuation of the laser frequency was reduced from 2.36 MHz (rms) to 1.07 MHz (rms) in 1 h by optimizing the voltage of the piezoelectric translator.

用于多普勒测风雷达的单频全固态激光器稳频

The master laser of an injection-seeded laser for Doppler wind lidar is frequency stabilized to a Fabry-Perot (FP) cavity using Pound-Drever-Hall technique. The FP cavity is specially designed to gain high temperature stability with Zerodur cavity and spacer. A computer based controller is used to sample and process the error signal. After the master laser is locked, the relative frequency drift is +-25 kHz in 1 s, and +-5 kHz in 1 h, which can satisfy the need of Doppler wind lidar.

Spectral-gate injection seeding in tunable lasers

A new concept, defined as spectral-gate injection seeding, is proposed for coupling the master oscillator (MO) and the forced oscillator (FO) in tunable injection-seeding laser systems. It is based on the use of a spectral selector as a tunable narrowband spectral gate between the partially coupled MO and FO cavities. The concept proposed enables one to implement compact and efficient injection-seeded tunable lasers. It is demonstrated experimentally on Nd:YAG-laser pumped dye lasers with a Fizeau interferometer as a spectral gate. Full suppression of the FO’s broadband spectral background is acheived even when the MO operates near the threshold.

Magneto-optic trap of Rb atoms with an injection-seeded laser that operates at two frequencies

We captured Rb atoms in a magneto-optic trap by using two frequencies in an injection-seeding process of a diode laser without the use of a separate repumping laser. In the incomplete injection-seeding condition, the power of the free-running slave laser at the repumping frequency can be partially converted into power at the master laser frequency, which is stabilized at the cooling frequency. We measured conversion efficiencies and frequency shifts based on the injecting power and the preset frequency difference between the master laser and the slave laser.

Detection of weak signals via the decay of an unstable state: Initiation of an injection-seeded laser.

We have demonstrated the detection of weak optical signals via the decay of an unstable state. A {ital Q}-switched laser is an example of an unstable state, the decay of which has to be triggered either by quantum fluctuations or by an injected external signal. Measurement of the initiation time of the laser intensity allows us to determine the strength of the external signal with a dynamic range of 7 orders of magnitude. It is possible to detect signal levels that correspond to less than one photon in a selected cavity mode.

Excess spontaneous emission in non-Hermitian optical systems. I. Laser amplifiers.

Petermann first predicted in 1979 the existence of an excess-spontaneous-emission factor in gain-guided semiconductor lasers. We show that an excess spontaneous emission of this type, and also a correlation between the spontaneous emission into different cavity modes, will in fact be present in all open-sided laser resonators or optical lens guides. These properties arise from the non-self-adjoint or non-power-orthogonal nature of the optical resonator modes. The spontaneous-emission rate is only slightly enhanced in stable-resonator or index-guided structures, but can become very much larger than normal in gain-guided or geometrically unstable structures. Optical resonators or lens guides that have an excess noise emission necessarily also exhibit an ``excess initial-mode excitation factor'' for externally injected signals. As a result, the excess spontaneous emission can be balanced out and the usual quantum-noise limit recovered in laser amplifiers and in injection-seeded laser oscillators, but not in free-running laser oscillators.