Nonplanar Ring Cavity Research Articles

Method for calculating the optical axis position in laser cavities

We present a method for calculating the optical axis contour in laser cavities using the geometric optics approximation. The deviation of the position of the optical axis in four-mirror nonplanar ring cavities is calculated for various cavity perturbations. Various types of laser cavities are considered and classified according to their symmetry. Deviations of the optical axis are determined in a nonplanar ring cavity that provides Kerr mode locking operation. A formula is given that relates the bend angle in four-mirror cavities to the angles of radiation incidence on the mirrors.

Direct generation of a narrow-linewidth Laguerre-Gaussian vortex laser in a monolithic nonplanar oscillator.

Vortex laser beams carrying orbital angular momentum have been attracting a lot of interest in recent years. Here we demonstrate the direct generation of a vortex laser in a monolithic nonplanar ring cavity. The unidirectional and single-frequency operation of Laguerre-Gaussian modes is observed and characterized. Fork interferograms have been obtained using a simple interferometer based on a plano-concave lens, and the topological charge of vortex beam is determined. A spectral linewidth as narrow as 2.3kHz is measured by beating with a reference laser. We believe that such a high coherent vortex laser can be beneficial for numerous applications, including precision measurements and optical communications.

Continuous-wave single-frequency 589 nm yellow laser generated from sum frequency of single-block non-planar ring cavity laser in periodically poled KTiOPO4 crystal

Continuous-wave single-frequency 589 nm yellow laser can be used in laser cooling of sodium atoms. Besides, the interaction between 589 nm laser and sodium atoms can be studied by resonance fluorescence, which provides an important basis for the sodium guide star in the adaptive optics. In this paper, single frequency 589 nm yellow light is generated by sum frequency of single-block non-planar ring cavity 1064 nm and 1319 nm laser in periodically poled KTiOPO4 crystal. The geometric parameters of single-block non-planar Nd:YAG crystal and magnetic field intensity are optimally designed by simulation calculation through using Jones matrix. The output powers 1080 mW and 580 mW are obtained for continuous-wave single-frequency 1064 nm and 1319 nm laser in the experiment, respectively The two fundamental beams are expanded to be the same as perfectly as possible in size and are focused into a spot with a size of about 60 m by an achromatic lens. The sum-frequency generation takes place in a 1 mm2 mm20 mm phase-matched type-I periodically poled KTiOPO4 crystal with a matching temperature of 55℃ and polarization period of 12.35 m The crystal is anti-reflection coated for all three wavelengths (1064 nm, 1319 nm and 589 nm). A 14.8 mW output of 589 nm laser is obtained with beam quality factor M2=1.14 and the corresponding sum-frequency efficiency is 0.9%. The influence of periodically poled KTiOPO4 temperature on the sum-frequency efficiency is studied and the temperature acceptance bandwidth is measured to be 1.5 degrees The wavelength of 589 nm yellow light can be tuned to the sodium atom D2a absorption line by changing the temperature of 1064 nm Nd:YAG crystal and 0.164 pm of tuning accuracy is reached. The whole laser system is stable and reliable, so it provides a practical and effective technical means to obtain the continuous-wave single-frequency 589 nm laser, for it is relatively simple and easy to implement.

Novel non-planar ring cavity for enhanced beam quality in high-pulse-energy optical parametric oscillators

A novel non-planar ring cavity is presented. It is shown that by using a fractional image rotation, i.e. a rotation whose angle cannot be expressed as 2π/n, where n is a small integer, the number of modes that can oscillate in the cavity is greatly reduced. This Fractional Image Rotation Enhancement (FIRE) cavity can thus be used to increase the beam quality in cases of low transversal mode discrimination, such as lasers with large pump and beam size and high-pulse-energy optical parametric oscillators (OPOs), especially when compactness and efficiency are key parameters. The experimental results obtained with a FIRE OPO for mid-IR (3–5 μm) generation based on a ZnGeP2 crystal pumped by a Ho3+:LiLuF4 MOPA system at 2.05 μm are compared to those realized with the same crystal and pump arrangement using a standard Rotated Image Singly-Resonant Twisted RectAngle (RISTRA) cavity. An increase of the beam quality from M2 of 2.08–2.29 to M2 of 1.88–1.99 is reached at 20 mJ pulse energy when the FIRE cavity is used.

Analysis of optical axis variations in monolithic nonplanar ring laser

A mathematical model of the mirror misalignment of a four-equal-sided nonplanar ring cavity is established in this letter. The variations in the optical axis are discussed through an augmented 6 \times 6 ray matrix formulation. Numerical analysis shows that the self-consistence of the optical axis can always be obtained because of the thermal effects in any case of mirror misalignment. For a fabricated design, optical axis variations always appear. The influence of thermal effects (i.e., pump power) on optical axis variations are studied. The tilt of the optical axis remains constant, whereas its decentration varies with pump power. Further analysis shows that the actual closing point of the optical axis moves close to the ideal point as the pump power increases. The theoretical analysis proposed is proven and validated by the experimental results.

Nonplanar ring resonator modes: generalized Gaussian beams

Several findings on the modes of a nonplanar ring resonator have been carried out by utilizing the matrix method of generalized Gaussian beams. The widely used nonplanar ring resonator--a four-equal-sided nonplanar ring cavity with two curvature mirrors and two planar mirrors--has been chosen as an example. The overall stability maps of this typical nonplanar ring cavity with L/R ranging from 0 to infinity are calculated and described, while the total cavity length is L and the radius of the curvature mirrors is R. The stability map has also been found to have asymmetry with total image rotation rho ranging from 0 degrees to 360 degrees and 0<L/R<2. It has also been found that there still exist several stable regions in the extended region with L/R>2. The Gaussian modes of the nonplanar ring cavity have been found to have different characteristics with different design parameters such as rho and L/R. The azimuth angles of the major and minor axes of the spot size have been found to be variable with different design parameters such as rho and L/R and variable under different location of the nonplanar cavity. These interesting findings are totally different from the behavior of conventional planar stable resonators and are important to the cavity designs of nonplanar ring resonators.

Planar Multipass Ring Laser Cavity

A planar multipass ring laser is demonstrated using a pair of spherical mirrors. The reentrant conditions of ring cavities are derived. The stabilities of laser cavities are also analyzed. A 3 atm.% Nd-doped YAG crystal of 1 mm thickness was used as the gain medium. The laser output is polarized even for cubic gain media. The polarization ellipticity is increased by a factor of 23.8 in a planar ring cavity compared with that in a nonplanar ring cavity.

Unidirectional Single-Mode 532-nm Nd:YAG Laser Using Intracavity Frequency Doubling in Nonplanar Ring Geometry

Intracavity frequency doubling of a single-mode Nd:YAG laser using a nonplanar ring cavity is demonstrated. The nonplanar ring cavity consists of a Brewster-angled Nd: YAG crystal placed in a magnetic field, a KTP crystal, and two spherical mirrors. In this design the Nd:YAG crystal acts as both a nonreciprocal polarization rotator and a partial polarizer, and the nonplanar portion of the ring cavity, which is formed by a relative twist angle between the Brewster-angled end surfaces of the crystal, serves as a reciprocal polarization rotator. Eigenpolarization theory for the cavity configuration is presented and a suitable value of the relative twist angle for unidirectional operation is estimated. A single-mode output power of 22 mW at 532 nm is obtained with a 1.2-W diode laser at 809 nm and a laser linewidth of less than 100 kHz is inferred from a beat note frequency spectrum between two identical laser systems.

비평면 고리형 공진기를 이용한 단일 모드 Nd:YAG 레이저의 내부 공진기 주파수 배가

비평면 고리형 공진기에서의 내부 공진기 주파수 배가를 이용한 단일 모드 Nd:YAG 레이저를 제작하였다. 비평면 고리형 공진기는 두 개의 구면경과 Nd:YAG 결정, KIP 결정으로 구성되어 있다. Nd:YAG 결정의 양단면은 상대적인 비틀림 각을 갖고 있으면서 브루스터 각이 되도록 연마되었으며, 비틀림 각에 의해 형성된 비평면 고리 공진기가 가역적인 편광 회전기 역할을, 자기장이 가해진 Nd:YAC 결정 자체가 비가역적 편광 회전기 역할을, 브루스터 각을 갖고 있는 양단면이 편광자 역할을 각각 담당하여 전체적으로 광 다이오드를 형성하고 있다. 이러한 구조에서 단 방향 발진이 일어날 수 있는 비틀림 각이 이론적으로 추정되었다. 1.2 W, 809 nm 다이오드 레이저로 펌핑하여 532 nm 파장에서 22 ㎽의 단 방향, 단일 모드 출력을 얻었으며, 이것은 약 1.8%의 변환 효율에 해당한다. Intracavity frequency doubling of a single-mode Nd:YAG laser by using a nonplanar ring cavity is demonstrated. The nonplanar ring cavity consists of a Brewster-angled Nd:YAG crystal placed in a magnetic field, a KTP crystal, and two spherical mirrors. In this design the Nd:YAG block acts as both a nonreciprocal polarization rotator and a partial polarizer, and the nonplanar portion of the ring cavity, which is formed by a relative twist angle between the Brewster-angled end surfaces of the Nd:YAG block, serves as a reciprocal polarization rotator. An eigenpolarization theory for the cavity configuration is presented and suitable values of the relative twist angle for unidirectional operation are estimated. A single-mode output power of 22 ㎽ at 532 nm and an optical to optical conversion efficiency of 1.8% are obtained with a 1.2 W diode laser at 809 nm.

PICO-WATT AND FEMTO-WATT WEAK-LIGHT PHASE LOCKING

Advances in laser physics and its applications have triggered the proposition and development of Laser Astrodynamics. In carrying out research projects on Laser Space Programs, it is necessary to process the laser signal sent back from remote spacecraft. After traveling an extremely long distance, the power of this signal is greatly reduced. Weak-light phase-locking is the key technique used for signal amplification in these space projects. After the returning laser beam is collected by telescope, it is used to phase-lock a local laser oscillator. The local laser then carries the phase information of the remote spacecraft laser. we used diode-pumped non-planar ring cavity Nd:YAG lasers to serve as the remote weak-light laser and the local strong-light laser. We then built an optical phase-locked loop to phase-lock them. The weak-light laser signal was simulated using ND (neutral density)-filters to decrease the light intensity. In the phase detection, we used balanced detection to eliminate laser intensity noise and improve the S/N ratio. Combining this with an appropriate loop filter, we were able to control the laser frequency and improve the phase-locking ability. We phase-locked a 2 nW weak-light beam and a 2 mW strong-light beam with a 57 mrads(rms)phase error. The locking duration was very long. Locking of a 200 pW and a 2007thinsp;μW light beam, with phase error of 200 mrad (rms) and duration of over 2 hours was achieved. The phase error for locking a 200 μW to a 20pW light beam was 160 mrad (rms). The locking duration was also longer than 2 hours. the last locking performed was carried out with a 2 pW and a 200 μW light beam. The phase error and the locking duration were 290 mrad(rms) and 1.5 min respectively.

Interferometric measurement of low-frequency phase noise characteristics of diode laser-pumped Nd:YAG ring laser

We report the interferometric measurement of the phase noise characteristics of a diode laser-pumped solid-state Nd:YAG 1.3μ laser based on a nonplanar ring cavity. Results show that the device has a low-frequency phase noise approximately three orders of magnitude lower than that observed with semiconductor diode lasers. The use of this source in fibre sensing applications is discussed.

Mode Interactions in Four-frequency Degeneracy-lifted Ring Lasers

Abstract A non-planar ring cavity, with a non-reciprocal bias in the form of the longitudinal Zeeman effect on the gain medium, has been used to demonstrate four-mode bidirectional operation in a He-Ne ring laser at 632·8 nm. It has also been shown that this ring system is sensitive to rotation.

Polarization Frequency Splitting in Non-planar Ring Laser Resonators

Abstract A non-planar ring cavity has been used to demonstrate polarization frequency splitting providing reciprocal bias for a multi-oscillator ring laser gyroscope. A bias of 94 MHz has been observed for a cavity with a longitudinal mode spacing (c/L) of 260 MHz. The bias agrees well with the passive cavity splitting predicted by a Jones matrix analysis of the cavity. The application of a non-reciprocal bias, in the form of the Zeeman effect on the gain medium, has demonstrated four-mode operation in a He-Ne ring laser operating at 632·8 nm.