YAG Ring Laser Research Articles

4.08 mJ, 0.976 μs Er: YAG ring laser oscillator

Er:YAG ring laser with high-energy and wide pulse duration, which is resonantly pumped by a fiber laser at 1532 nm, is reported in this paper. Maximum power 2.62 W was implemented from ring resonator at 1645 nm. By transforming pulse repetition frequency (PRF), pulsed output energy was 4.08 mJ under 100 Hz PRF with a pulse width of 0.976 μs under the Q-switching regime. Since the wind measurement accuracy of coherent wind lidar is determined by the pulse width of the emission laser, this 1.6 µm single-frequency laser with high energy and wide pulse width is an ideal laser source for coherent wind lidar.

High efficiency tunable unidirectional single-longitudinal-mode Er:YAG ring laser based on an acousto-optic modulator

A wavelength tunable single-longitudinal-mode (SLM) Er:YAG ring laser around 1.6 µm is demonstrated. By using an acousto-optic modulator (AOM) to force unidirectional operation, up to 10.4 W and 8.7 W SLM laser output power are obtained at 1645.22 nm and 1617.33 nm, with corresponding slope efficiencies of 45% and 40%, respectively. Besides, stable dual-wavelength operation at both 1645 nm and 1617 nm is also achieved with the maximum power of 9.1 W. By rotating the birefringent filter (BRF) in the ring cavity, the wavelength could be tuned from 1616.77 nm to 1617.51 nm and 1644.51 nm to 1646.12 nm. The line width is measured to be 125 kHz at 1617 nm and 131 kHz at 1645 nm via the time-delayed self-heterodyne method. As far as we know, 8.7 W is the highest continuous-wave SLM output power at 1617 nm.

A 1-kHz Single Frequency Nd:YAG Ring Laser by Injection Seeding**Supported by the National Key Research and Development Program of China under Grant No 2017YFB1104500, and the National Natural Science Foundation of China under Grant No 61875100.

We report on an injection seeded 1 kHz single frequency pulsed Nd:YAG ring laser with pulse energy of 5.2 mJ and pulse width of 9.9 ns. The ramp-fire technique is used to maintain single frequency operation and the cavity length is modulated by an intracavity RbTiOPO4 (RTP) crystal. The frequency stability (rms) of the output pulse is 1.99 MHz over 1 min and the linewidth is 64 MHz.

Novel single-frequency Nd:YAG ring laser by reducing the depolarization loss

A principle study on reducing the depolarization loss in a single-frequency Nd:YAG ring laser by a novel ring resonator configuration is reported. In the resonator, one cavity mirror with 99.5% reflectivity at 1064 nm for 45-degree incident s-polarized light and about 75% transmissivity for 45-degree incident p-polarized light was employed. Besides, the transmissivity for the 45-degree incident p-polarized and s-polarized light for the output-couple mirror were 32% and 3.5%, respectively. The cavity mirror and the output-couple mirror were utilized as the polarizer to enforce the s-polarized beam unidirectionally operating in the resonator. 2.1 W single-frequency output at 1064 nm with elliptical polarization was obtained from this ring resonator. Compare with the existent Nd:YAG ring resonator, this novel resonator has a potential advantage in reducing depolarization loss and increasing the efficiency.

Single-Frequency Side-Diode-Pumped Monopulse Nd:YAG-Laser with a Ring Cavity

The formation features of the single-frequency unidirectional monopulse lasing mode of a Nd:YAG laser with a triple-mirror ring cavity and a side diode-pump with injection of external narrow-band optical radiation into the cavity are studied. The asymmetric layout of the intracavity elements relative to the output mirror and depolarization effects in them cause the energy and polarization of the monopulse Nd:YAG ring laser to differ depending on the input direction (clockwise or counterclockwise) of the injected radiation. The difference in the output characteristics of the single-frequency unidirectional monopulse Nd:YAG ring laser is most evident for a change from active to passive Q-switching.

Spiking suppression of high power QCW pulse 1319 nm Nd:YAG laser with different intracavity doublers

We describe the results of our efforts in suppressing spiking of a high power, high beam quality 1319 nm Nd:YAG microsecond-pulse laser with three different intracavity frequency doublers. The 1319 nm laser is generated by a quasi-continuous-wave diode-pumped Nd:YAG ring laser system. One potassium titanyl phosphate (KTP), two KTPs and one lithium triborate (LBO) as frequency doublers are installed in the ring resonator and tested, respectively. At 800 Hz repetition rate, with a pulse width of 100 µs, performances of spiking suppression for each case are observed. The average output power are 23.6 W, 22.7 W and 23.4 W with beam quality factors of M2 = 2.21, 1.28 and 1.25 for one KTP, two KTPs and one LBO, respectively. The corresponding brightness are 270 MW/(cm2·sr), 780 MW/(cm2·sr) and 860 MW/(cm2·sr). With better beam quality, higher brightness, and easier maintainability, the LBO is the best option of the three. A laser rate equation model including the insertion loss of the doubler is applied for theoretical analysis of the output temporal pulse shape and power, and the simulated results agree well with the experimental data.

Performance of a dual-end-pumped Er:YAG ring laser at room temperature

We demonstrated continuous-wave (CW) and Q-switched operation of a room-temperature Er:YAG ring laser that is dual-end-pumped by a laser diode at 1532 nm. For the continuous-wave regime, a maximum output power of 4.6 W at 1645.1 nm was obtained under the pump power of 27 W and threshold of about 19 W, corresponding to the slope efficiency of 54.3% with respect to the pump power and optical-to-optical conversion efficiency of 17%. For the Q-switched regime, the maximum pulse energy of 3.91 mJ and the minimum pulse width of 106 ns at the repetition rate of 100 Hz was achieved.

Synchronisation of self-oscillations in a solid-state ring laser with pump modulation in the region of parametric resonance between self-modulation and relaxation oscillations

The synchronisation of the self-modulation oscillation frequency in a Nd : YAG ring laser by an external periodic signal modulating the pump power in the region of parametric resonance between self-modulation and relaxation oscillations is studied theoretically and experimentally. The characteristic features of synchronisation processes in lasers operating in the self-modulation regime of the first kind and in the regime with a doubled self-modulation period are considered. Two bistable branches of synchronisation of self-modulation oscillations are found by numerical calculation. The experimental data agree well with the numerical simulation results for one of these branches, but the other branch of bistable self-modulation oscillations was not observed experimentally.

Resonantly pumped monolithic nonplanar Ho:YAG ring laser with high-power single-frequency laser output at 2122 nm

We demonstrated a stable single-frequency laser operating at 2122 nm from a monolithic nonplanar Ho:YAG ring oscillator (NPRO). The Ho:YAG NPRO was resonantly pumped by a 1907 nm Tm:YLF laser built up by ourselves. The maximum multimode output power from the Ho:YAG NPRO was 9.66 W and the slope efficiency was 71.7%. With accurate adjustment of the pump position to make the laser oscillate in single frequency condition, an output power of 8.0 W was obtained with a slope efficiency of 61.4% and an optical-optical efficiency of 50.0%. The power stability of the Ho:YAG NPRO laser was 0.29% at maximum single frequency output power. The beam quality M(2) factors were measured to be less than 1.1 in x- and y- directions.

Continuous-wave and Q-switched operation of a Ho:YAG ring laser in-band pumped at 1908 nm

We demonstrated continuous-wave (CW) and Q-switched operation of a Ho:YAG ring laser in-band pumped at 1908 nm. A maximum CW output power of 2.2 W at 2122.35 nm was obtained under an incident pump power of 13.2 W, corresponding to a slope efficiency of 26%. For the Q-switched regime a maximum output energy of 5.2 mJ at a repetition rate of 100 Hz was achieved. A shortest pulse width of 200 ns was achieved, corresponding to a peak power of 26 kW.

885 nm pumped, high efficiency single-frequency Nd:YAG ring laser

We report an efficient single-frequency ring laser pumped directly into emitting level by a fiber-coupled laser diode (FCLD) at 885 nm for the first time. 4.8 W laser at 1064 nm was obtained in a 0.7 at % Nd:YAG with 63% slope efficiency and 51.7% light-light efficiency in absorbed pump power. At the same time, the line width of the longitudinal mode was about 50 MHz, and the beam was nearly diffraction-limited with M2 ≈ 1.07.

A High Power Single Frequency Diode Side-Pumped Nd:YAG Ring Laser

We demonstrate a high-power single-frequency diode-side pumped Nd:YAG laser at 1064 nm. A bow-tie ring cavity configuration comprising two plane and two curved mirrors with two-rod birefringence compensation is employed. The influence of length Lx between two curved mirrors on output power and beam quality is investigated theoretically and experimentally while the separation of the flat mirrors is set to be 656 mm and the fold angle is 10°. When the pump powers are 358, 343 and 329 W at 808 nm, the maximal output powers of 31.9, 26 and 14.1 W are obtained with beam quality factors M2 = 1.41, 1.12 and 1.20 for Lx = 205, 215 and 230 mm, respectively.

Diode-pumped actively Q-switched Tm:YAG ring laser operation at room temperature

2-μm lasers with high pulse energy and long pulse width of hundreds of nanoseconds are needed urgently in the accurate wind velocity lidar systems. This paper presents the acoustic-optical Q-switched Tm:YAG laser performance in a pulsed-laser-diode end-pumping figure-eight ring resonator structure. Pulse energy and pulse width are investigated with the increasing of the incident pump energy at different repetition rate operation. Maximum energy of 4.6 mJ with the pulse width of 179.2 ns and 3.57 mJ with pulse width of 184.4 ns are obtained at the repetition rate of 20 and 100 Hz, respectively. Under free-running and Q-switched operation, the peak output wavelength is 2.014 μm at all time, and the beam quality factors are lower than 2 times diffraction-limited measured by a knife-edge traveling method.

Generation of tunable and narrow linewidth continuous-wave yellow laser by sum–frequency mixing of diode-pumped solid-state Nd:YAG ring lasers

We report a tunable, narrow linewidth and high beam quality continuous-wave (CW) yellow laser system at 589 nm. The system is an all solid-state design employing single-pass sum–frequency generation in a KTP crystal by mixing the 1064 nm with 1319 nm lines of two side-pumped Nd:YAG enforcing unidirectional ring lasers. With this method, a CW yellow laser at 589.159 nm with an output power of 0.8 W, a linewidth less than 1.5 GHz and a beam quality M 2 = 1.29 is obtained. The wavelength of the laser also can be precisely tuned from 589.112 to 589.181 nm in step-length of about 0.22 pm.

Continuous-wave cavity-ringdown detection of stimulated Raman gain spectra

Cavity ringdown (CRD) spectroscopy, with its high sensitivity, provides a novel way to perform continuous-wave (cw) stimulated Raman gain (SRG) spectroscopy, rather than by conventional optically detected coherent Raman techniques. Tunable cw laser light at ∼1544 nm is used to probe ringdown decay from a rapidly-swept, high-finesse optical cavity containing a gas-phase sample of interest and itself located inside the cavity of a cw single-longitudinal-mode Nd:YAG ring laser operating at ∼1064.4 nm. This approach is used to measure cw SRG spectra of the ν 1 fundamental rovibrational Raman band of methane gas at ∼2916.5 cm−1. The resulting SRG-CRD resonances have ringdown times longer than in the off-resonance case, in contrast to the usual shorter ringdown times arising from absorption and other loss processes. Previously reported noise-equivalent sensitivities have been substantially improved, by using a second ringdown cavity to facilitate subtraction of infrared-absorption background signals. Moreover, by employing a ringdown cavity in the form of a ring, the SRG-pump and CRD-detected Stokes beams can co-propagate uni-directionally, which significantly reduces Doppler broadening.

Spike suppression and longitudinal mode selection in a 1.319 μm Nd:YAG laser by high-efficiency intracavity frequency doubling

We describe a flashlamp pumped 1.319 μm Nd:YAG ring laser in which a high-efficiency intracavity frequency doubler is used as a nonlinear output coupler, virtually eliminating all spiking behavior and providing longitudinal mode selection as well. A single frequency, long pulse (>50 μs) output at 660 nm with about 20 W peak power is produced, suitable as a source for visar and other applications where long coherent pulses at relatively high power are required. Experimental results and theoretical analyses are given.

Frequency jitter and spectral width of an injection-seeded Q-switched Nd:YAG laser for a Doppler wind lidar

The design of a 50 Hz single longitudinal mode, diode-pumped and frequency-tripled Nd:YAG master oscillator power amplifier is described, and the first measurements of output parameters are presented. The laser oscillator is injection-seeded by a tuneable monolithic Nd:YAG ring laser and frequency stabilized by minimising the Q-switch build-up time. The laser system will be an integral part of an airborne instrument demonstrator for a first satellite based Doppler wind lidar to measure vertical profiles of one component of the atmospheric wind vector. This paper focuses on the investigation of the frequency jitter and the linewidth of the laser, which are measured on a pulse-to-pulse basis. For this purpose a compact, high accuracy beat frequency monitoring system has been developed at DLR. By operating the amplifier stage at half the repetition rate (50 Hz) of the oscillator, we could reduce the frequency stability from 10 MHz (rms) to 1.3 MHz (rms) (over a 14 s period). We have determined a mean linewidth of 15 MHz (FWHM) at 1064 nm. These measured laser parameters enable wind velocity measurements in the atmosphere (0–15 km) at an accuracy of 1 to 2 m/s.

Efficient and Compact Yb:YAG Ring Laser

An efficient and compact Yb:YAG ring laser was demonstrated with a slope efficiency of 39.0% with respect to the absorbed power. The design issues for using Yb:YAG as the gain medium in the reentrant multipass ring laser are discussed. The high absorption coefficient and low quantum defect of Yb:YAG make it an ideal gain medium for the multipass ring cavity to fulfil reentrant condition and reduce reabsorption loss. The absorption characteristics of a 20-at.% doped Yb:YAG crystal and the optimum ratio of absorption depth to Yb:YAG thickness were measured. The degrees of linear polarization were 99.0% and 94.1% in planar N=2 and nonplanar (N,M)=(2,1) ring lasers, respectively. The multipass ring cavities can be applied in a compact mode-locked laser with long round-trip length.

Continuous-wave stimulated Raman gain spectroscopy with cavity ringdown detection

Cavity ringdown (CRD) spectroscopy is extended for the first time from its conventional optical-absorption mode of operation into the regime of coherent Raman spectroscopy. Continuous-wave (cw) stimulated Raman gain (SRG) spectra of the 2916.5-cm-1 ν1 rovibrational fundamental Raman band of methane (CH4) gas are measured, using tunable cw laser light at ∼1544 nm to probe ringdown decay from a rapidly swept optical cavity that is itself inside the cavity of a cw single-longitudinal-mode Nd:YAG ring laser operating at ∼1064.5 nm. The resulting change of ringdown decay rate is dependent on pump laser irradiance and is associated with Raman gain. Remarkably, such SRG-CRD resonances display ringdown times that are longer than in the off-resonance case, contrasting with the usual reduction of ringdown time associated with absorption and other loss processes.

1 W of stable single-frequency output at 1.03 μm from a novel, monolithic, non-planar Yb:YAG ring laser operating at room temperature

We demonstrate, for the first time to our knowledge, a longitudinally diode-pumped, monolithic ytterbium ion-doped YAG non-planar ring laser (NPRO). We achieved a continuous-wave (cw) single-frequency output power of 1 W with 45.0% slope efficiency and a beam quality factor of M(2)<1.1. In view of iodine frequency stabilization we have characterized the frequency tuning properties and have measured the relative intensity noise. Additionally, 6.1 mW second harmonic power at 515 nm was achieved using a periodically poled KTP crystal in a single-pass setup.