This PDF file contains the front matter associated with SPIE Proceedings Volume 12902, including the Title Page, Copyright information, Table of Contents, and Conference Committee information.

This is a tribute to Mansoor Shiek-Bahae who passed away July 10, 2023, the first day of the Hawaii Nonlinear Optics conference in Honolulu. See obituaries in Ref. [1]. Mansoor was scheduled to give an invited talk that morning but sent his postdoc Alex Albrecht to give the talk due to his illness.[2] It was a shock for all of us at the conference to have to announce his death there. My presentation at Photonics West will be my third talk about Mansoor’s contributions to the field of nonlinear optics. Of course, Mansoor is also well-known for his pioneering contributions to laser cooling which will be outlined by his former student, Denis Seletskiy, in this conference.

This paper reports a second generation of radiation-balanced fiber laser and amplifier cooled internally using anti-Stokes fluorescence by pumping them at 1040 nm. In both devices the gain medium is a single-mode silica fiber with a core heavily doped with Yb³⁺, initially encapsulated in CaF₂ nanoparticles, and co-doped with Al to reduce quenching and increase the cooling efficiency. After optimization of its length (4.1 m) and its output coupler reflectivity (3.3%), the 1065- nm continuous-wave fiber laser has a threshold of 160 mW and a radiation-balanced (no net heat generation) output power of 192 mW, or nearly 70% higher than the previous radiation-balanced fiber laser. At its radiation-balanced point, its optical efficiency is 56.8%. The single-frequency, single-mode fiber amplifier, constructed with the same fiber, was optimum with a length of 6.8 m, and it had a radiation-balanced gain of 20 dB: it amplified an 800-μW signal to 84.2 mW with 433 mW of input pump power. The significance of this result is underscored by the small diameter of the single-mode fiber core (7.8 μm), which makes cooling more challenging. This study further demonstrates the viability of achieving substantial gain and energy extraction in a small-core Yb-doped silica fiber while effectively utilizing anti-Stokes fluorescence to keep it cool.

Unitary control changes the optical absorption and emission of an object by transforming the external modes. We answer two basic questions: Given an object, what absorptivity, emissivity, and their difference are attainable via unitary control? How to obtain given absorptivity, emissivity, and their difference? We show that both questions can be answered using the mathematics of majorization.

Recent experiments with optically levitated particles have shown incredible promise for high-precision sensing of accelerations and gravitational fields as well as exploring mesoscopic physics. One barrier that often stands in the way of improved acceleration sensitivity or quantum state coherence time is high particle temperatures due to absorption of the light from the trapping laser. In optically levitated acceleration sensing architectures, one limitation on the precision of such sensors is often the upper limit on the size of the particle that can be trapped: larger particles require more laser power to levitate, but too much absorption of the trapping light can overheat and vaporize the particles. We present a novel, detailed analysis on a levitated optomechanical accelerometer to understand what combinations of acceleration sensitivities and maximum-tolerated accelerations can be reasonably achieved, and we analyze the extent to which anti-Stokes optical refrigeration may solve the problem of overheating particles. We also analyze the effect of blackbody radiation pressure shot noise on a force and acceleration sensor concept involving free-falling particles that are released and recaptured by an optical trap. We find that, while optical refrigeration is likely insufficient to solve the problem of large particles vaporizing in high-power traps, it would help mitigate blackbody radiation pressure shot noise in future accelerometers based on free-falling particles.

Radiative cooling, taking advantage of the coldness of the sky, has a potential to be a sustainable alternative to meet cooling needs. The performance of a radiative cooling device is fundamentally limited by the emissivity of the sky, therefore depends heavily on the regional weather conditions. Although the sky emissivity is known to increase with the dew point temperature, the feasibility of radiative cooling remains elusive in the equatorial tropical climate, where the weather is humid, cloudy and constantly changing. We point out that a high degree of thermal insulation of the radiative cooling system can be effective under such extreme weather conditions. A new method to characterise dynamic sky conditions is presented, namely to measure the sky window emissivity in the zenith direction. We show that a sub-ambient cooling up to 8 °C is possible during daytime and that the cloud base is not a complete blackbody and can be used as a heat sink for radiative cooling.

For applications of laser cooling, silica optical fibers provide beneficial mechanical, chemical, and thermal fortitude, and they also offer compatibility with current commercial fiber laser systems. This paper explores the influence of hydroxyl concentrations on heat generation in ytterbium-doped aluminosilicate fibers produced using modified chemical vapor deposition (MCVD).

We have successfully synthesized near-infrared photoluminescent erbium-doped lithium yttrium fluoride nanocrystals using a facile coprecipitation approach. The nanocrystals are capped with oleic acid, enabling dispersion in nonpolar solvents such as toluene and cyclohexane. The relative amounts of yttrium and erbium precursors were adjusted during the synthesis to obtain different concentrations of Er between 1% and 15%. The composition and structure of the nanocrystals were studied via X-ray fluorescence spectroscopy and X-ray powder diffraction. The nanocrystals were optically characterized by extensive photoluminescence studies, including Stokes and anti-Stokes emission. When excited with 1.55-μm light, the nanocrystals displayed strong anti-Stokes emission associated with the ⁴I_13/2 → ⁴I_15/2 transition. These nanocrystals therefore have a high potential to be used in optical cooling applications with telecommunication-wavelength excitation.