Open-aperture Z-scan study for absorption saturation: accurate measurement of saturation intensity in YLF:Yb for optical refrigeration
Azzurra Volpi, Jackson Kock, Alexander R. Albrecht, Markus P. Hehlen, Richard I. Epstein, Mansoor Sheik‐Bahae
Abstract
Knowledge of saturation intensity of gain or absorption plays a fundamental role in a variety of applications ranging from lasers to many nonlinear optical processes. Here, we present an analytical expression for open-aperture Z-scan transmission for accurately measuring the saturation intensity in the low absorbance samples but at arbitrary pump intensities. We exploit this formalism to investigate the absorption saturation of <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"> <mml:mrow class="MJX-TeXAtom-ORD"> <mml:msub> <mml:mrow class="MJX-TeXAtom-ORD"> <mml:mi mathvariant="normal">L</mml:mi> <mml:mi mathvariant="normal">i</mml:mi> <mml:mi mathvariant="normal">Y</mml:mi> <mml:mi mathvariant="normal">F</mml:mi> </mml:mrow> <mml:mn>4</mml:mn> </mml:msub> </mml:mrow> <mml:mo>:</mml:mo> <mml:mrow class="MJX-TeXAtom-ORD"> <mml:msup> <mml:mrow class="MJX-TeXAtom-ORD"> <mml:mi mathvariant="normal">Y</mml:mi> <mml:mi mathvariant="normal">b</mml:mi> </mml:mrow> <mml:mrow class="MJX-TeXAtom-ORD"> <mml:mn>3</mml:mn> <mml:mo>+</mml:mo> </mml:mrow> </mml:msup> </mml:mrow> </mml:math> (YLF:Yb) in the anti-Stokes excitation region for optical refrigeration at high pump intensities. An absorption saturation intensity of <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"> <mml:mn>14.5</mml:mn> <mml:mo>±</mml:mo> <mml:mn>1</mml:mn> <mml:mrow class="MJX-TeXAtom-ORD"> <mml:mi mathvariant="normal">k</mml:mi> <mml:mi mathvariant="normal">W</mml:mi> </mml:mrow> <mml:mrow class="MJX-TeXAtom-ORD"> <mml:mo>/</mml:mo> </mml:mrow> <mml:mrow class="MJX-TeXAtom-ORD"> <mml:msup> <mml:mrow class="MJX-TeXAtom-ORD"> <mml:mi mathvariant="normal">c</mml:mi> <mml:mi mathvariant="normal">m</mml:mi> </mml:mrow> <mml:mn>2</mml:mn> </mml:msup> </mml:mrow> </mml:math> was measured in YLF:Yb at 1020 nm ( <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"> <mml:mrow class="MJX-TeXAtom-ORD"> <mml:mi mathvariant="normal">E</mml:mi> </mml:mrow> <mml:mrow class="MJX-TeXAtom-ORD"> <mml:mo stretchy="false">|</mml:mo> </mml:mrow> <mml:mrow class="MJX-TeXAtom-ORD"> <mml:mo stretchy="false">|</mml:mo> </mml:mrow> <mml:mi>c</mml:mi> </mml:math> ) at room temperature.