RU2638078C1 - Compact infrared solid-state laser - Google Patents

Abstract

FIELD: physics.

SUBSTANCE: compact infrared solid-state laser contains a pumping laser and a crystal of Fe²⁺:ZnSe - a passive q - switching dye, while translucent and reflective dielectric coatings are applied on the crystal face of Fe²⁺:ZnSe parallel to the optical axis of the pumping laser.

EFFECT: enabling the realisation of compact laser emitter of the IR range with a reduced number of optical elements.

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Description

The invention relates to the field of laser physics and can be used to develop sources of laser radiation of the middle infrared (IR) range (3.95 ... 5.05 microns).

In the framework of [1], the generation of a high-power small-sized Er: YLF laser with diode pumping in the Q-switching mode by a passive gate on an Fe ²⁺ : ZnSe crystal was realized. A matrix of laser diodes was used as the pump source. The active element of the laser (Er: YLF, activator concentration 15 at.%) Had the shape of a cylinder with dimensions of 02x35 mm. A dielectric coating was applied to one of the ends of the active element, acting as a deaf mirror for radiation generation and an antireflection coating for pump radiation. An antireflection coating was applied to the second end.

The pump radiation was introduced into the active element according to the longitudinal-transverse scheme, implemented using a system of prisms of total internal reflection. The laser cavity was formed by a flat dull mirror sprayed at the end of the active element and an external spherical output mirror (radius of curvature 1.2 m, reflection coefficient 0.85 or 0.95). Two Fe ^{2+ were} used in the experiments: a ZnSe gate with different initial transmission.

In device [2], the radiation of a laser based on a YAG: Er ³⁺ crystal with a generation wavelength of 2.94 μm, operating in the regime of active Q-switching, was focused by a cylindrical lens (in a line about 10 mm long and ~ 100 μm wide) onto the crystal surface ZnSe containing a layer enriched in Fe ^{2+ ions} , the pump pulse duration was ~ 100 ns. Superluminescence radiation was detected in the direction along the focusing line of the pump in the region of the crystal immediately adjacent to its surface. The faces through which the radiation exited the crystal were chipped off. The axis of the radiation beam was a continuation of the pump line with allowance for refraction at the crystal face. Therefore, a resonator providing feedback for radiation was absent.

In [3], a setup was presented for the study of a Fe: ZnSe laser (the concentration of Fe ^{2+ ions} was 2.5 × 10 ¹⁸ cm ^-3 ) when radiation was pumped by an Er: YAG laser operating in the free-running mode. The active element was a parallelepiped with transverse dimensions of 9.7 × 10.1 mm and a length (gain length) of 7.7 mm, the ends of which were polished and not brightened. To reduce the inversion dump by amplified spontaneous noise propagating in the direction transverse to the optical axis of the resonator, the side surfaces of the crystal were matted and covered (blackened) with aquadag. The Fe: ZnSe laser resonator is formed by a “deaf” spherical mirror with a radius of curvature of 1000 mm and a plane translucent mirror. The transmittance of the output mirror at the generation wavelength was 72%, and the cavity length was 350 mm. The radiation beam of an Er: YAG laser focused into a spot with a diameter of 6 mm (95% of energy) was incident on a Fe: ZnSe crystal at an angle of 3 ° to the optical axis of the cavity.

Closest to the proposed invention is the device described in [4, 5], where it is indicated that lasing on a Fe ²⁺ : ZnSe crystal was first achieved at room temperature when pumped with short (50 ns) Er: YAG laser pulses (2.94 μm ), launched in the Q-switched mode with the help of also a Fe ²⁺ : ZnSe crystal, but with a lower Fe concentration [4].

In the device [5], the active element for the Fe ²⁺ : ZnSe laser was made from a Fe ²⁺ : ZnSe single crystal grown from the vapor phase by free growth using a single crystal seed. Doping with Fe ^{2+ ions} to a concentration of ~ 1 × 10 ¹⁸ cm ^-3 was carried out directly during growth. The active element of the pump laser had a length of 10 mm in the transverse size of 17 × 10 mm. The resonator was formed by a rear spherical mirror (radius of curvature 50 cm) and a flat output mirror with interference coatings deposited on a CaF ₂ substrate. A Fe ²⁺ : ZnSe crystal was installed near the output mirror at a Brewster angle to the optical axis of the resonator. The Fe ²⁺ : ZnSe laser was pumped by radiation from an Er: YAG laser with a radiation wavelength of 2.94 μm in the passive Q-switching mode of the cavity. A passive shutter in an Er: YAG laser was a plane-parallel plate made of a Fe ²⁺ : ZnSe single crystal.

A common disadvantage of the devices [1-5] is the use of two crystals of Fe ²⁺ : ZnSe to obtain laser radiation of the mid-IR range. One crystal is used as a passive Q-switched resonator for the pump laser to increase the power of the pump pulse. The second is for direct generation of laser radiation in the mid-IR range. Moreover, in device [3], special measures are taken to disrupt the generation of Fe ²⁺ : ZnSe in the crystal in the direction transverse to the optical axis of the pump laser cavity.

The closest in technical essence to the present invention is an infrared solid-state laser [6], in which one crystal of Fe ²⁺ : ZnSe is used simultaneously as a passive Q-switch and as an active element. For this, the Fe ²⁺ : ZnSe crystal has a parallelepiped shape and is located inside the pump laser cavity. Moreover, on the crystal face, perpendicular to the optical axis of the pump laser, an antireflection dielectric coating is applied with a maximum transmission at the wavelength of the pump laser. On the crystal edge, parallel to the optical axis of the pump laser, an antireflection dielectric coating is applied with a maximum transmission at the required wavelength of the mid-IR range (3.95 ... 5.05 μm). The pump laser cavity is a rear spherical and front plane-parallel mirrors with interference coatings deposited on a substrate of CaF ₂ or some other optical material that is transparent in the infrared region of the spectrum. The coatings of both mirrors have a maximum reflection at the wavelength of the pump laser, forming a “deaf” semi-confocal resonator. The resonator and the active medium made of an Er: YAG crystal are a pump laser.

To output the mid-IR radiation, a resonator is installed parallel to the faces of the Fe ²⁺ : ZnSe crystal with a coated antireflection dielectric with a maximum transmission at the required wavelength of the mid-IR range (3.95 ... 5.05 μm). The disadvantage of the device [6] is the presence of an additional resonator, which requires additional laborious adjustment, and also increases the number of optical elements of the device, generally reducing its reliability.

The objective of the invention is to obtain a compact laser emitter of the infrared range with a reduced number of expensive optical elements. To do this, on the edge of a Fe ²⁺ : ZnSe crystal (passive Q-switch - laser active medium), parallel to the optical axis of the pump laser, translucent and reflective optical coatings (dielectric or metal interference coatings) are applied for the mid-IR wavelength (3.95 ... 5.05 μm).

The device operates as follows. The Fe ²⁺ : ZnSe crystal has a parallelepiped shape and is located inside the pump laser cavity. The pump laser cavity is a rear spherical and front plane-parallel mirrors with interference coatings deposited on a substrate of CaF ₂ or some other optical material that is transparent in the infrared region of the spectrum. The coatings of both mirrors have a maximum reflection at the wavelength of the pump laser, forming a “deaf” semi-confocal resonator. The resonator and the active medium made of an Er: YAG crystal are a pump laser. The presence of translucent and reflective optical coatings provides the presence of positive feedback in the Fe ²⁺ : ZnSe crystal, thus forming laser radiation of the mid-IR range.

In FIG. 1 presents a diagram of the invention, where the numbers denote: 1 - active medium - crystal Er: YAG; 2 - pump radiation; 3 - semiconfocal "deaf" resonator for a wavelength of 2.94 microns; 4 - crystal Fe ²⁺ : ZnSe (passive Q-switch - laser active medium); 5 - translucent optical coating for a wavelength of the mid-IR range (3.95 ... 5.05 microns); 6 - reflective optical coating for a wavelength of the mid-IR range (3.95 ... 5.05 microns); 7 - crystal faces of Fe ²⁺ : ZnSe, enlightened for a wavelength of 2.94 μm; 8 - radiation of a pump laser (2.94 μm); 9 - laser radiation of the middle infrared range.

Literature

1. Inochkin M.V., Nazarov V.V., Sachkov D.Yu., Khloponin L.V., Hramov V.Yu., Korostelin Yu.V., Landman A.I., Podmarkov Yu.P., Frolov M.P. Small Er: YLF laser with passive Fe ²⁺ : ZnSe shutter. "Optical Journal", 79, 6, 2012, p. 31-35.

2. Ilyichev NN, Danilov V.P., Kalinushkin V.P., Studenikin M.I., Shapkin P.V., Nasibov A.S. Superluminescent IR emitter based on a ZnSe: Fe crystal operating at room temperature. Quantum Electronics. 2008, Volume 38, No 2, p. 95-96.

3. Velikanov S.D., Zaretsky N.A., Zotov E.A., Kozlovsky V.I., Korostelin Yu.V., Krokhin ON, Maneshkin A.A., Podmarkov Yu.P., Savinova S.A., Skasyrsky Y.K., Frolov M.P., Chuvatkin R.S., Yutkin I.M. Investigation of the operation of a Fe: ZnSe laser in pulsed and pulsed-periodic modes. Quantum Electronics. 45, No. 1 (2015), p. 1-7.

4. Landman A.I. Vapor-phase growth of single crystals of compounds A ^II B ^VI doped with transition metals for mid-IR lasers. Theses for the degree of candidate of physical and mathematical sciences. M .: Physical Institute. P.N. Lebedev RAS. 2008, 118 p.

5. Akimov V.A., Voronov A.A., Kozlovsky V.I., Korostelin Yu.V., Landman A.I., Podmarkov Yu.P., Frolov M.P. Efficient laser generation of a Fe ²⁺ : ZnSe crystal at room temperature. Quantum Electronics. 36, No. 4 (2006).

6. RU No. 2593819, 2016

Claims (1)

A small-sized infrared solid-state laser containing a pump laser, a Fe ²⁺ : ZnSe crystal is a passive Q-switch, characterized in that a translucent and reflective dielectric coating is applied on the edge of the Fe ²⁺ : ZnSe crystal parallel to the optical axis of the pump laser.

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