Digital laser for on-demand intracavity selective excitation of second harmonic higher-order modes

Abstract

In this article, we demonstrate selective excitation of second harmonic higher-order modes inside a diode end-pumped solid-state laser resonator that comprises of a nonlinear potassium titanyl phosphate (KTP) crystal and a digitally addressed holographic end-mirror in a form of a reflective phase-only spatial light modulator (SLM). The emitted second harmonic higher-order modes at 532 nm are generated by an intracavity nonlinear KTP crystal that is pumped by high-order fundamental modes operating at 1064 nm. The fundamental modes are digitally controlled by displaying a computer-generated hologram in the form of a grey-scale image to the SLM screen for on-demand high-order modes. The phase matching of the fundamental mode to the generated frequency-doubled mode is achieved by controlling the phase of the digital hologram to either achieve a high or quasi-degree of orbital angular momentum conservation. We show that we can intracavity generate frequency-doubled high-order Laguerre-Gaussian modes and Hermit-Gaussian modes that are either quasi or fully reproducible in the far-field. To the best of our knowledge, this is the first laser to generate frequency-doubled on-demand higher-order modes inside the cavity at the visible (green) wavelength of 532 nm.

Evolution on spatial patterns of structured laser beams: from spontaneous organization to multiple transformations

“…Meanwhile, for the intracavity nonlinear process of structured laser beams, some studies also showed similar properties, while more complex and diverse beam patterns can be obtained 146 – 150 …”

“…The transition patterns from one to the other allow visualization of lasing across vastly differing OAM values as superpositions with two concentric rings. Then, in a digital laser for on-demand intracavity selective excitation of second-harmonic higher-order modes, an SLM used for structured beam generation also acted as an end mirror of the laser resonator, 147 as shown in Fig. 9(b1).…”

“…Meanwhile, for the intracavity nonlinear process of structured laser beams, some studies also showed similar properties, while more complex and diverse beam patterns can be obtained. [146][147][148][149][150] The timeline of the evolution on spatial patterns of structured laser beams is shown in Fig. 1.…”

Nonlinear optics with structured light

“…Most of these solutions have been at low power. Nonlinear laser amplifiers have been used to raise the power levels, both in bulk crystals 105 and disks 106 with vectorial light, including parameteric amplification of ultrafast structured light 107 , and with scalar structured light in Erbium fibre amplifiers 108 as well as by Raman amplification 109 .…”

Second harmonic generation of laser beams in transverse mode locking states

“…Compared with the aforementioned approaches, intracavity generation of a second harmonic beam provides a promising method to obtain the SHG of complex transverse modes with relatively low energy or power consumption. 26 Even the SHG of some on-demand complex basic transverse modes 27 and the SHG of some transverse modes with optical lattices 28 were investigated recently; there were rarely clear investigations of the SHG of laser beams in TML states. Different from the traditional study on the nonlinear frequency conversion of a longitudinal mode-locked ultrafast laser beam, the variation of spatial structure information is focused on nonlinear frequency conversion of a TML beam.…”