Abstract An effective approach to obtain a single-frequency laser with low intensity noise is presented in this paper, which is implemented by employing a gain medium with the small stimulated-emission cross section (SECS). When the adopted Nd:YAP (Nd:YAlO 3 ) gain medium with SECS of 4.6×10 −19 cm 2 is replaced by Nd:CYA (Nd:CaYAlO 4 ) gain medium with SECS of 1.04×10 −19 cm 2 , the frequency of measured intensity noise reached shot noise limit obviously reduces from 2.49 to 1.5 MHz, which agrees well with the theoretical predictions. On this basis, a single-frequency continuous-wave (CW) Nd:CYA laser with low intensity noise is first achieved. The attained output power of the Nd:CYA laser is 1.12 W. The achieved single-frequency CW 1080 nm laser will satisfy the requirements of the squeezed and entangled light generation.
Abstract An effective approach to obtain a single-frequency laser with low intensity noise is presented in this paper, which is implemented by employing a gain medium with the small stimulated-emission cross section (SECS). When the adopted Nd:YAP (Nd:YAlO 3 ) gain medium with SECS of 4.6×10 −19 cm 2 is replaced by Nd:CYA (Nd:CaYAlO 4 ) gain medium with SECS of 1.04×10 −19 cm 2 , the frequency of measured intensity noise reached shot noise limit obviously reduces from 2.49 to 1.5 MHz, which agrees well with the theoretical predictions. On this basis, a single-frequency continuous-wave (CW) Nd:CYA laser with low intensity noise is first achieved. The attained output power of the Nd:CYA laser is 1.12 W. The achieved single-frequency CW 1080 nm laser will satisfy the requirements of the squeezed and entangled light generation.
Continuous-wave, single-frequency, solid-state lasers with long-term frequency stability and low-intensity noise are an essential resource to generate squeezed and entangled states of light. In order to obtain the stable, nonclassical states of light, the frequency of the laser has to be stabilized with a stable reference. Due to the zero expansion property at a certain temperature, an ultra-low expansion (ULE) Fabry-Perot (F-P) cavity with a high finesse can be used as one of the best candidates of the frequency reference. We perform a detailed analysis of an extraordinarily high-frequency stability and ultra-low-intensity noise laser based on an improved cascade Pound-Drever-Hall frequency stabilization to a ULE F-P cavity. The frequency drift of the laser is suppressed to 7.72 MHz in 4 hours, and the noise level of the laser is simultaneously reduced to the quantum noise limit in the frequency below 300 kHz, which provides the possibility for the direct generation of a stable, high-level squeezed state in a lower-frequency region.
We demonstrate the generation of 20.2 W of continuous-wave, low-intensity noise, single-frequency light at 840 nm, obtained via sum-frequency mixing of two high-power infrared fiber laser systems in an MgO-doped periodically poled lithium niobate (ppLN) crystal. Subsequent cavity-enhanced frequency doubling to 420 nm yields an output power of 15.2 W. Respective conversion efficiencies of 48% and 79% are achieved for the sum-frequency and second-harmonic stages, with good beam quality (M 2 < 1.3), low intensity noise (<0.05% RMS [1 kHz–10 MHz]), and long-term continuous operation. Relative intensity noise and frequency noise of the generated signals are experimentally characterized.
The Nd:YAG laser is a solid state laser that has many applications in the industry, science and medicine. We in this paper use a continuous wave (CW) Nd:YAG laser emitting light at 1064 nm to generate random numbers. We first give a recipe of an experimental setup that is capable of measuring and recording the vacuum fluctuations with the help of our cw Nd:YAG laser. The basic scheme simply involves the Nd:YAG laser, detectors and some radio frequency electronic components. The laser source used in the demonstration provides us with a quantum noise limited CW at a radio frequency sideband of 14 MHz. The final data obtained after appropriate electronic signal processing are digitized voltage fluctuations that correspond to the vacuum fluctuations in the optical domain. The data randomly lies above or below zero due to its quantum mechanical probabilistic nature. We assign a '1' to the data that is positive and a '0' to the data that is negative, hence we are able to generate a random bit sequence by using a cw Nd:YAG laser. This result adds yet another interesting application to the many number of broad applications of the Nd:YAG laser system.
We developed a fiber-laser-pumped Ti:sapphire laser system designed for quantum precision measurement applications. By employing a 35 W single-frequency 532 nm fiber laser as the pump source, the system delivered continuous-wave output powers of 4.12 W at 770.108 nm (D 1 line, K), 4.72 W at 780.244 nm (D 2 line, Rb), and 5.29 W at 794.982 nm (D 1 line, Rb), thereby fulfilling the requirements for optical pumping and probing of alkali atoms. To enhance frequency stability, saturated absorption spectroscopy was used to lock the laser frequency, resulting in frequency drifts below 1 MHz over two hours. Furthermore, since low-frequency intensity noise (DC-100 Hz) critically affects spin-relaxation-free quantum sensing, we carried out a theoretical analysis which identified the pump laser as the dominant noise source. By implementing feedback control to the pump source as well as an external noise suppression, both methods achieved over 30 dB of intensity noise suppression within the DC-4kHz frequency range. In addition, improved beam pointing stability further reduced noise below 3 Hz. These results collectively demonstrate the system’s strong potential for quantum sensing applications.
Continuous variable (CV) audio-band frequency squeezed states at the fiber telecommunication wavelength is an important quantum resource for the practical applications based on optical fiber. As is well known, the optical power attenuation and phase diffusion effect of light at 1.3 μm in standard telecommunication fibres are low and small, respectively. The audio-band frequency squeezed light at 1.34 μm can be utilized to realize quantum precision measurement, such as quantum-enhanced sensing in the low-frequency range, laser interferometer for gravitational wave detection. In this paper, CV audio-band frequency vacuum squeezed states at 1.3 μm are experimentally generated by using a type-I degenerate optical parametric oscillator (DOPO) below the threshold. A home-made continuous-wave single-frequency dual-wavelength (671 nm and 1.34 μm) Nd:YVO4/LBO laser is used as a pump source for DOPO based on a type-I quasi-phase-matched periodically poled KTiOPO4 (PPKTP) crystal. Mode cleaners with a finesse of 400 and linewidth of 0.75 MHz are used to filter the noise of lasers at 671 nm and 1.34 μm, respectively. The intensity noises of the two lasers reach a shot noise level for analysis frequencies higher than 1.0 MHz and their phase noises reach shot noise level for analysis frequencies higher than 1.3 MHz, respectively. The low noise single-frequency 671 nm laser is utilized as a pump of the DOPO. The threshold power of the DOPO is 450 mW. In order to detect the audio-band frequency vacuum squeezed states, the power of local oscillator of a homodyne detector system is optimized to 60 μupW. Furthermore, the effect of common mode rejection ratio (CMRR) of detectors is discussed in detecting the audio-band frequency vacuum squeezed states. Improvement of CMRR of detectors is a good way to detect the audio-band frequency vacuum squeezed states effectively. When the phase matching temperature of PPKTP crystal is controlled at 53℃ by using a home-made temperature controller and the pump power is 95 mW, the vacuum squeezed states are generated at analysis frequency ranging from 8-100 kHz. A maximum measured squeeze of 5.0 dB is obtained at analysis frequency of 36 kHz. A 3.0 dB squeezed light is obtained at an audio-band frequency of 8 kHz.
Continuous variable (CV) quantum entanglement is a fundamental resource of CV quantum communication and quantum computation. It is useful in a wide variety of applications, including quantum teleportation, quantum dense coding, quantum key distribution, and high-precision quantum measurement. In this paper, we generate CV quantum entanglement at a telecommunication wavelength of 1342 nm by using a nondegenerate optical parametric amplifier (NOPA) with a type-Ⅱ periodically poled KTiOPO4 (PPKTP) crystal. A home-made continuous-wave single-frequency dual-wavelength (671 nm and 1342 nm) Nd:YVO4/LiB3O5 laser is achieved with output powers of 1.5 W (671 nm) and 1.3 W (1342 nm). Then a mode cleaner (MC1) with a fineness of 400 and linewidth of 0.75 MHz and a mode cleaner MC2 with a fineness of 400 and linewidth of 0.75 MHz are used to filter the noises of laser at 1342 nm and 671 nm, respectively. By using MCs, the intensity noise of laser reaches a shot noise level (SNL) for analysis frequencies higher than 1.0 MHz, and the phase noise of laser reaches an SNL for analysis frequencies higher than 1.3 MHz. Utilizing this kind of low noise single-frequency 671 nm laser as a pump, a doubly-resonant optical parametric oscillator with a threshold of 325 mW is realised. When the low noise single-frequency 1342 nm laser is injected as a signal and the relative phase between the pump and injected signal is locked to , the NOPA is operated at deamplification. After optimizing the temperature of the type-Ⅱ PPKTP crystal and at a pump power of 260 mW, Einstein-Podolsky-Rosen (EPR)-entangled beams with quantum correlation of 3.0 dB for both the amplitude and phase quadratures are experimentally generated. The strength of EPR-entangled beams is relatively low. It is maybe due to the low nonlinear conversion efficiency and large absorption of the type-Ⅱ PPKTP crystal at 671 nm and 1342 nm. The generated CV quantum entanglement at 1.34 m has lower transmission loss and smaller phase diffusion effect in a silica fiber. The research contributes to a high quality quantum source for the CV quantum communication based on existing telecommunication fiber networks.