Single-frequency Continuous-wave Laser Research Articles

Compact high-power 320-nm continuous-wave single-frequency laser based on power scaling of a diode-pumped Pr:LiYF4 ring laser at red.

Single-frequency (SF) lasers in the visible spectral region are usually obtained through an indirect method, i.e., frequency doubling of near-infrared SF lasers. In this work, we report on the direct generation of a high-power continuous-wave (CW) SF laser in red based on a diode-pumped Pr:LiYF4 (YLF) ring cavity technology. A maximum output power is scaled to 3.98 W at 640 nm with a linewidth of about 17.2 MHz and a power stability of 0.6%. Moreover, by inserting a LBO crystal into the ring cavity for intracavity frequency doubling of the 640 nm SF laser, we have also successfully demonstrated an ultraviolet (UV) SF laser at 320 nm, for the first time to the best of our knowledge, with a maximum power of 670 mW. This work provides a promising route for the development of simple, compact, and high-power SF lasers operating in visible and UV spectral regions.

High-power single-frequency continuous-wave 355 nm UV laser via a frequency-correlated dual-wavelength laser.

An all-solid-state single-frequency continuous-wave (CW) 355 nm ultraviolet (UV) laser based on a dispersion-compensated doubly resonant resonator is presented in this Letter that is achieved by employing homemade high-stability all-solid-state frequency-correlated dual-wavelength lasers at 1064 and 532 nm and a temperature-controlled type-I critical-phase-matching LiB3O5 (LBO) to act as the fundamental laser source and the nonlinear medium, respectively. The frequency-correlated dual-wavelength single-frequency CW laser supplies the fundamental frequency 1064 and 532 nm lasers with good frequency synchronization. And the temperature-controlled LBO acts as the dispersion-compensation element to realize double resonance of the 1064 and 532 nm laser. Finally, a 4.2 W high-stability 355 nm UV laser is experimentally obtained, and the corresponding total conversion efficiency is up to 20.5%. To the best of our knowledge, this is the highest power reported about single-frequency CW 355 nm UV laser. The presented method can pave a way to develop a compact single-frequency 355 nm UV laser with high output power.

A novel tuning range search method for single soliton state micro-comb generation

Abstract Mode-locked single-soliton state micro-comb (SSC) can be achieved in a miniaturized highly compact platform by pumping the micro-resonator with a single-frequency continuous wave laser. However, a significant challenge lies in effectively exploring the tuning range of pump power, spanning over hundreds of mW, as well as the detuning range and tuning speed in the range of hundreds of MHz and the order of MHz/s to GHz/s respectively. Here, we delve into a simulation model, considering thermal effects to ensure that the simulation accurately reflects the power drop and thermal detuning observed in the experimental process. Our simulation model, featuring precision scanning and iterative parameter demonstrations, has proven instrumental in accurately exploring the optimal tuning range for the existence of SSC to a few MHz. This provides a foundation for controlled and predictable SSC generation experiments.

208 W single-frequency 1064 nm laser based on a single-crystal fiber master-oscillator power amplifier.

High-power all-solid-state continuous-wave (CW) single-frequency laser with high linear polarization is a significant source for quantum optics and precision measurement. In this Letter, a high-power linearly polarized CW single-frequency laser based on the single-crystal fiber (SCF) master-oscillator power amplifier (MOPA) is presented, in which a homemade 140 W low-noise CW single-frequency laser and a Nd:YAG SCF are firstly employed as the seed laser and the medium of the MOPA, respectively. The mode-matching between the pump laser propagated with waveguide form and the freely propagated seed laser is optimized by considering the influence of the degradations of the polarization and the beam quality. Finally, when the incident powers of the pump and seed lasers are 262.6 W and 126.3 W, respectively, the seed waist radius is optimized to 200 μm. In this case, the output power of the linearly polarized laser reaches up to 208 W, which is the highest output power, to the best of our knowledge. The presented results provide a good reference for implementing a high power and high degree of the polarization and good beam quality laser based on the SCF MOPA.

Research progress on enhancing the output power of all-solid-state single-frequency continuous-wave lasers by using intracavity nonlinear loss mode-selecting technology (invited)

Research progress on enhancing the output power of all-solid-state single-frequency continuous-wave lasers by using intracavity nonlinear loss mode-selecting technology (invited)

Characterization of the Carrier Lensing Effect in a Second Harmonic Generator

This paper presents studies on the carrier lensing effect of a tapered amplifier in a compact cavity-enhanced second harmonic generator. When different injecting currents are applied, carriers in the tapered amplifier are depleted to different levels depending on the local optical field intensity, resulting in a spatial variation of the refractive index and creating an effective convex lens for the amplified laser beam. This can significantly reduce the mode matching between the pump beam and the cavity, leading to a degradation of the second harmonic generator efficiency. To characterize this effect and provide guidance for mode matching, the evolution of optical fields and carriers in the tapered amplifier is simulated numerically with Maxwell-Bloch equations. The effective focal length of the tapered amplifier is calculated theoretically and verified with experimental calibration. Based on these results, the coupling optics of the cavity can be properly designed so as to achieve a high coupling efficiency. Finally, a single-frequency continuous-wave laser at 461 nm is achieved, with an output power exceeding 500 mW and a conversion efficiency of 33%.

Self-mode-matching compact low-noise all-solid-state continuous wave single-frequency laser with output power of 140 W.

The high power all-solid-state continuous wave single-frequency laser is a significant source for science and application due to good beam quality and low noise. However, the output power of the laser is usually restricted by the harmful thermal lens effect of the solid gain medium. To address this issue, we develop a self-mode-matching compact all-solid-state laser with a symmetrical ring resonator in which four end-pumped Nd:YVO4 laser crystals are used for both laser gain media and mode-matching elements. With this ingenious design, the thermal lens effect of every laser crystal can be controlled and the dynamic of the designed laser including the stability range and the beam waist sizes at crystals can be manipulated only by adjusting the pump power used on each laser gain medium. Under an appropriate combination of pump powers on four crystals, self-mode-matching in a resonator is realized. A stable CW single-frequency at 1064 nm with 140-W power, 102-kHz linewidth, and low intensity noise is obtained. The presented design paves an effective way to further scale-up the output power of a compact laser by employing more pieces of gain media.

Integrated femtosecond pulse generator on thin-film lithium niobate.

Integrated femtosecond pulse and frequency comb sources are critical components for a wide range of applications, including optical atomic clocks1, microwave photonics2, spectroscopy3, optical wave synthesis4, frequency conversion5, communications6, lidar7, optical computing8 and astronomy9. The leading approaches for on-chip pulse generation rely on mode-locking inside microresonators with either third-order nonlinearity10 or with semiconductor gain11,12. These approaches, however, are limited in noise performance, wavelength and repetition ratetunability10,13. Alternatively, subpicosecond pulses can be synthesized without mode-locking, by modulating a continuous-wave single-frequency laser using electro-optic modulators1,14-17. Here we demonstrate a chip-scale femtosecond pulse source implemented on an integrated lithium niobate photonic platform18, using cascaded low-loss electro-optic amplitude and phase modulators and chirped Bragg grating, forming a time-lens system19. The device is driven by a continuous-wave distributed feedback laser chipand controlled by a single continuous-wave microwave source without the need for any stabilization or locking. We measure femtosecond pulse trains (520-femtosecond duration) with a 30-gigahertz repetition rate, flat-top optical spectra with a 10-decibel optical bandwidth of 12.6 nanometres, individual comb-line powers above 0.1 milliwatts, and pulse energies of 0.54 picojoules. Our results represent a tunable, robust and low-cost integrated pulsed light source with continuous-wave-to-pulse conversion efficiencies an order of magnitude higher than those achieved with previous integrated sources. Our pulse generator may find applications in fields such as ultrafast optical measurement19,20 or networks of distributed quantum computers21,22.

Recent progress in continuously tunable low-noise all-solid-state single-frequency continuous-wave laser based on intracavity locked etalon

All-solid-state single-frequency continuous-wave (CW) lasers have been applied in many fields of scientific research owing to their intrinsic advantages of high beam quality, low noise, narrow linewidth, and high coherence. In atom-based applications, single-frequency lasers should also be continuously tuned to precisely match their wavelengths with the transition lines of the corresponding atoms. Continuous frequency tuning of the laser is mainly achieved by continuously scanning the laser cavity length after the intracavity tuning element etalon is locked to an oscillating laser mode. However, the modulation signals necessary in current etalon locking systems increase the noise of the continuously tunable lasers and in some respects limit their applications in Frontier scientific research. Moreover, the obtained continuous frequency tuning range with the etalon locking technique is restricted by the free spectrum range of the adopted etalon. In this paper, we systematically summarize recent progress of the continuously tunable single-frequency CW lasers based on intracavity locked etalon, including the advanced etalon locking techniques and the tuning range expansion approach. As a result, the low noise and high stable all-solid-state single-frequency CW tunable lasers are successfully developed.

Performance Improvement of Single-Frequency CW Laser Using a Temperature Controller Based on Machine Learning.

The performance improvement of an all-solid-state single-frequency continuous-wave (CW) laser with high output power is presented in this paper, which is implemented by employing a temperature control system based on machine learning to control the temperature of laser elements including gain crystal, laser diode and so on. Because the developed temperature controller based on machine learning combines the back propagation (BP) neural network algorithm with the proportion-integration-differentiation (PID) control algorithm, the parameters of the PID are adaptive with the variation of the environment. As a result, the control speeds and control abilities of the temperatures of the elements are dramatically enhanced. In this case, the output characteristic and the adaptability to the environment as well as the stability of the single-frequency CW laser are also improved greatly.

Single-frequency continuous-wave laser based on the novel Er/Yb-doped composite phosphosilicate fiber

Optical and laser properties of a new Er/Yb-doped composite optical fiber manufactured according to the “rod-in-tube” technique are presented. The fabricated composite fiber with a standard outer diameter of 125 μm was single-mode at the wavelength of 1.55 μm. A Fabry-Perot laser cavity was manufactured on a 25 mm long fiber segment using the femtosecond technique of Bragg gratings inscription. The resulting laser with an effective cavity length of 12 mm generated strictly continuouswave single-frequency radiation at a wavelength of 1548.3 nm at room temperature (295 K). The key advantage of the studied Er/Yb-doped composite fiber laser is the excellent temporal stability of the laser output without any tendency for self-excited oscillation mode at any pump level.

60.4 W continuous-wave single-frequency laser output from a two-stage Nd:YAG single-crystal fiber amplifier.

A Nd:YAG single-crystal fiber amplifier for the amplification of continuous-wave single-frequency laser end-pumped by a laser diode (LD) is investigated. With a two-stage amplification configuration, an output power of 60.4 W under the total incident pump power of 200 W is achieved, which is, to our knowledge, the highest power from a continuous-wave single-frequency laser achieved with a single-crystal fiber scheme. The extraction efficiency reaches 41.6% in the second amplification stage, which is comparable with Innoslab amplifiers. The beam quality factors M2 at the maximum output power in the horizontal and vertical direction are measured to be 1.51 and 1.38, respectively. The long-term power instability for 1 hour is 0.97%.

A Review of the High-Power All-Solid-State Single-Frequency Continuous-Wave Laser.

High-power all-solid-state single-frequency continuous-wave (CW) lasers have been applied in basic research such as atomic physics, precision measurement, radar and laser guidance, as well as defense and military fields owing to their intrinsic advantages of high beam quality, low noise, narrow linewidth, and high coherence. With the rapid developments of sciences and technologies, the traditional single-frequency lasers cannot meet the development needs of emerging science and technology such as quantum technology, quantum measurement and quantum optics. After long-term efforts and technical research, a novel theory and technology was proposed and developed for improving the whole performance of high-power all-solid-state single-frequency CW lasers, which was implemented by actively introducing a nonlinear optical loss and controlling the stimulated emission rate (SER) in the laser resonator. As a result, the output power, power and frequency stabilities, tuning range and intensity noise of the single-frequency lasers were effectively enhanced.

Injection-seeded backward terahertz-wave parametric oscillator

Engineered quasi-phase-matching in a periodically poled nonlinear crystal has enabled backward optical parametric oscillators, where a pump photon is down-converted to counterpropagating signal and idler photons without an optical cavity. Here, we demonstrate an injection-seeded backward terahertz-wave parametric oscillator (BW-TPO) based on a slant-strip-type periodically poled lithium niobate crystal. A continuous-wave single-frequency laser is used in the BW-TPO pumped by sub-nanosecond 1064.4-nm pulses to provide an injection seed beam for the forward-propagating idler wavelength at 1065.7 nm, resulting in over a 1000-fold enhancement in backward-propagating 0.335-THz output energy, a 63% reduction of the oscillation threshold, and a quantum conversion efficiency as high as 47%. Thanks to the unique advantage of cavity-less oscillation, these improvements and stable operation in the BW-TPO are achieved without any stabilization control of either seed or oscillation modes. Our results show that such an injection-seeded BW-TPO is promising as a compact, efficient, and robust THz-wave source for a wide variety of applications.

Influence of the pump scheme on the output power and the intensity noise of a single-frequency continuous-wave laser.

The influence of the pump scheme on the intensity noise of the single-frequency continuous-wave (CW) laser is investigated in this paper, which is implemented in a single-frequency CW Nd:YVO4 1064 nm laser by comparing the traditional 808 nm pumping scheme (TPS) to the direct 888 nm pumping scheme (DPS). Under the conditions that the lasers with TPS and DPS have the same cavity structure and the cavity mirrors, as well as the same operation state including the thermal lens of the laser crystals and the mode-matching between the pump laser mode and the laser cavity mode at the laser crystals, the output power of the laser with DPS is up-to 32.0 W, which is far higher than that of 21.1 W for the laser with TPS. However, the intensity noise of the DPS laser including resonant relaxation oscillation (RRO) frequency of 809 kHz, RRO peak amplitude of 31.6 dB/Hz above the shot noise level (SNL) and the SNL cutoff frequency of 4.2 MHz, respectively, is also higher than that of 606 kHz, 20.4 dB/Hz and 2.4 MHz for the TPS laser. After further analyses, we find that the laser crystal with high doping concentration and long optical length is employed for DPS laser in order to improve the pump laser absorption efficiency, which can simultaneously increase the dipole coupling between the active atoms and the laser cavity, and then results in a high RRO frequency with a large amplitude peak as well as a high SNL cutoff frequency of the laser.

掺Tm光纤MOPA准相位匹配单程倍频的单频激光器

In order to obtain a 0.9 μm near-infrared continuous-wave single-frequency laser output, a 50 mm long PPLN crystal was used to perform single-pass frequency doubling of the continuous-wave 1 925.08 nm single-frequency laser output of the Tm-doped fiber MOPA, and the temperature was matched by focusing parameters and quasi-phase optimized to achieve 96.95 nm second harmonic output up to 9.07 W at a fundamental optical power of 43.4 W, with a conversion efficiency of 20.9%.The second harmonic was in single longitudinal mode with M2 factors of 1.36 and 1.52 on x and y directions, respectively. The influence of focusing parameter and temperature on the conversion efficiency was experimentally investigated. The relationship between the focusing parameter and phase matching temperature acceptance was also discussed. The experimental results show that Tm-doped fiber laser quasi-phase matching one-way frequency doubling is an effective method to obtain 0.9 μm band continuous wave single frequency laser output.

Intensity noise suppression of a high-power single-frequency CW laser by controlling the stimulated emission rate.

The intensity noise of a high-power single-frequency continuous-wave (CW) laser is very harmful for applications in precise measurements and quantum communication. By simply lengthening the length of a laser resonator to decrease the stimulated emission rate of the laser, the coupling strength of all noise sources in the resonant laser field will be reduced, and thus the intensity noise of the output laser will be prominently suppressed. Based on theoretical analyses of the laser noise spectra, we experimentally implement a low-noise high-power single-frequency laser with a 1050 mm long resonator. With the assistance of an intracavity imaging system and nonlinear second-harmonic generation, the amplitude of the resonant relaxation oscillation peak and the shot-noise level (SNL) cutoff frequency are successfully reduced to 8.6 dB/Hz above SNL and 1.0 MHz, respectively, under the output power of 16 W. The work provides an effective way to develop a high-quality laser with high output power and low intensity noise.

125 W single-frequency CW Nd:YVO4 laser based on two-stage dual-end-pumped master-oscillator power amplifiers

We presented a 125 W single-frequency continuous-wave (CW) 1064 nm laser, where a homemade 50.3 W single-frequency CW high quality Nd:YVO4 laser and a two-stage dual-end-pumped master-oscillator power amplifier (MOPA) acted as the seed source and amplifier, respectively. As a result, a maximum output power of 125.2 W was achieved with the incident pump power of 200 W. The optical-to-optical conversion efficiency and the overall amplified power gain were 43.3% and 3.28%, respectively. The measured beam quality M2 and the long-term power stability of the 1064 nm amplifier during 8 h were better than 1.28 and ±0.73%, respectively. Additionally, the power extraction efficiency of the designed MOPA system was further investigated and the results revealed that the key of improvement of the power extraction efficiency of the MOPA system was employing a high-power single-frequency CW laser as the master oscillator.

Expanding Continuous Tuning Range of a CW Single-Frequency Laser by Combining an Intracavity Etalon With a Nonlinear Loss

Combining intracavity etalon (IE) locked on a laser oscillating mode with a deliberately introduced nonlinear loss, the tuning range of a continuous-wave (CW) single-frequency laser is significantly expanded to transcend the traditional limitation of a free spectral range (FSR) of IE. Due to the action of the nonlinear loss, the frequency of laser oscillating mode can be continuously and smoothly tuned without any mode-hopping in a tuning range much larger than FSR of IE. We theoretically analyze the physical mechanism behind the influence of nonlinear loss on the tuning range expansibility of the laser and experimentally demonstrated the effectiveness of the presented method. By means of this method, the ultrawide continuous frequency scanning range of 222.4 GHz at 532 nm is implemented. The theoretical analysis and the experimental results are in good agreement.

High-power 671 nm laser by second-harmonic generation with 93% efficiency in an external ring cavity.

Second-harmonic generation (SHG) is useful for obtaining single-frequency continuous-wave laser sources at various wavelengths for applications ranging from biology to fundamental physics. Using an external power-enhancement cavity is an effective approach to improve the frequency conversion efficiency. However, thermal effects limit the efficiency, particularly, in high-power operation. Therefore, reducing thermal effects is important when designing a cavity. This Letter reports the use of an external ring cavity for SHG, yielding a 5.2W, 671nm laser light with a conversion efficiency of 93.8±0.8% which, to the best of our knowledge, is a new record of conversion efficiency for an external ring cavity. It is achieved using a 10mm length periodically poled potassium titanyl phosphate crystal and a 65μm radius beam waist in the cavity so as to minimize thermal dephasing and thermal lensing. Furthermore, a method is developed to determine a conversion efficiency more accurately based on measuring the pump depletion using a photodiode detector and a maximum pump depletion up to 97% is recorded. In this method, the uncertainty is much less than that achieved in a common method by direct measuring with a power meter.