Realization of a high power optical trapping setup free from thermal lensing effects

Transmission of high power laser beams through partially absorbing materials modifies the light propagation via a thermally-induced effect known as thermal lensing. This may cause changes in the beam waist position and degrade the beam quality. Here we characterize the effect of thermal lensing associated with the different elements typically employed in an optical trapping setup for cold atoms experiments. We find that the only relevant thermal lens is represented by the $TeO_2$ crystal of the acousto-optic modulator exploited to adjust the laser power on the atomic sample. We then devise a simple and totally passive scheme that enables to realize an inexpensive optical trapping apparatus essentially free from thermal lensing effects

Optical characteristics of Nd:YAG optics and distortions at high power

The intensity profile and beam caustics of a fiber coupled high power Nd:YAG laser beam through a lens system are studied. The thermal lensing effect and its influence on the beam profile and focal position are discussed. Asymmetry of the intensity profile in planes above and below the focal plane is demonstrated. Also the influence of small pollutions on the protective window is explained. Three different methods are used to measure the occurrence\ud of thermal lensing and quantify these effects

Shock waves in thermal lensing

We review experimental investigation on spatial shock waves formed by the self-defocusing action of a laser beam propagation in a disordered thermal nonlinear media.Comment: 9 pages, 12 figure

Feedback control of thermal lensing in a high optical power cavity

This paper reports automatic compensation of strong thermal lensing in a suspended 80 m optical cavity with sapphire test mass mirrors. Variation of the transmitted beam spot size is used to obtain an error signal to control the heating power applied to the cylindrical surface of an intracavity compensation plate. The negative thermal lens created in the compensation plate compensates the positive thermal lens in the sapphire test mass, which was caused by the absorption of the high intracavity optical power. The results show that feedback control is feasible to compensate the strong thermal lensing expected to occur in advanced laser interferometric gravitational wave detectors. Compensation allows the cavity resonance to be maintained at the fundamental mode, but the long thermal time constant for thermal lensing control in fused silica could cause difficulties with the control of parametric instabilities.This research was supported by the Australian Research Council and the Department of Education, Science and Training and by the U.S. National Science Foundation, through LIGO participation in the HOPF

Heat generation and thermal lensing in 2.8-µm Er3+:LiYF4 lasers

Finite-element calculations of the population mechanisms in diode-end-pumped 3-µm Er:YLF lasers demonstrate that interionic-upconversion-induced multiphonon relaxations significantly increase heat generation, temperature gradients, and thermal lensing. This explains rod fracture above 1 W of output power

Compensation of Strong Thermal Lensing in High Optical Power Cavities

In an experiment to simulate the conditions in high optical power advanced gravitational wave detectors such as Advanced LIGO, we show that strong thermal lenses form in accordance with predictions and that they can be compensated using an intra-cavity compensation plate heated on its cylindrical surface. We show that high finesse ~1400 can be achieved in cavities with internal compensation plates, and that the cavity mode structure can be maintained by thermal compensation. It is also shown that the measurements allow a direct measurement of substrate optical absorption in the test mass and the compensation plate.Comment: 8 page

Characterization of thermal effects in the Enhanced LIGO Input Optics

We present the design and performance of the LIGO Input Optics subsystem as implemented for the sixth science run of the LIGO interferometers. The Initial LIGO Input Optics experienced thermal side effects when operating with 7 W input power. We designed, built, and implemented improved versions of the Input Optics for Enhanced LIGO, an incremental upgrade to the Initial LIGO interferometers, designed to run with 30 W input power. At four times the power of Initial LIGO, the Enhanced LIGO Input Optics demonstrated improved performance including better optical isolation, less thermal drift, minimal thermal lensing and higher optical efficiency. The success of the Input Optics design fosters confidence for its ability to perform well in Advanced LIGO

Analysis of heat generation and thermal lensing in erbium 3-µm lasers

The influence of energy-transfer upconversion (ETU) between neighboring ions in the upper and lower laser levels of erbium 3-µm continuous-wave lasers on heat generation and thermal lensing is investigated. It is shown that the multiphonon relaxations following each ETU process generate significant heat dissipation in the crystal. This undesired effect is an unavoidable consequence of the efficient energy recycling by ETU in erbium 3-µm crystal lasers, but is further enhanced under nonlasing conditions. Similar mechanisms may affect future erbium 3-µm fiber lasers. In a threedimensional finite-element calculation, excitation densities, upconversion rates, heat generation, temperature profiles, and thermal lensing are calculated for a LiYF4:Er3+ 3-µm laser. In the chosen example, the fraction of the absorbed pump power converted to heat is 40% under lasing and 72% under nonlasing conditions. The heat generation in a LiYF4:Er3+ 3-um laser is 1.7 and the thermal-lens power up to 2.2 times larger than in a LiYF4:Nd3+ 1-um laser under equivalent pump conditions, thus, also putting a higher risk of rod fracture on the erbium system