Laser module

A laser module comprising:

• a quantum cascade laser that includes:
• a substrate having a main surface and a back surface opposite to the main surface;
• a first clad layer provided on the main surface;
• an active layer provided on an opposite side of the first clad layer to the substrate;
• and
• a second clad layer provided on an opposite side of the active layer to the first clad layer,
• wherein the active layer has a first end surface and a second end surface facing each other in a second direction orthogonal to a first direction that corresponds to a stacking direction of the substrate, the first clad layer, the active layer, and the second clad layer,
• the first end surface constitutes a resonator for oscillating light of a first frequency and light of a second frequency, and
• the active layer generates a terahertz wave having a difference frequency between the first frequency and the second frequency;
• a diffraction grating unit that includes a movable diffraction grating constituting an external resonator for the light of the first frequency;
• a first lens disposed between the quantum cascade laser element and the movable diffraction grating and configured to transmit light emitted from the second end surface and light returning from the movable diffraction grating to the quantum cascade laser element;
• a second lens disposed at a position facing the first end surface and configured to transmit the terahertz wave emitted from the quantum cascade laser element;
• a first holder configured to hold the quantum cascade laser element;
• and
• a package that accommodates the quantum cascade laser element, the diffraction grating unit, the first lens, and the first holder and in which an optical path between a light incident surface of the second lens and the movable diffraction grating is disposed,
• wherein the first holder includes:
• a support surface on which the quantum cascade laser element is mounted;
• and
• a first side surface connected to the support surface and facing the first lens in the second direction,
• when viewed from a direction orthogonal to the first direction and the second direction, a first distance from an intersection point between the first side surface and the support surface to the second end surface along the second direction when a direction from the first lens toward the quantum cascade laser element along the second direction is a positive direction is smaller than a second distance between the intersection point and the first lens along the second direction,
• the package has a side wall facing the first end surface,
• the side wall has a through hole penetrating in a third direction perpendicular to the side wall,
• the through hole includes:
• a first hole portion that opens to an inside of the package;
• a second hole portion that opens to an outside of the package, and that includes the first hole portion and is larger than the first hole portion when viewed from the third direction;
• and
• an annular counterbore surface connecting the first hole portion and the second hole portion and extending along a plane intersecting the third direction,
• an outer edge portion of the light incident surface of the second lens is inserted into the second hole portion from the outside of the package and is fixed in surface contact with the counterbore surface,
• the first end surface is located inside the first hole portion, and
• the first holder further includes:
• a main body portion that includes a portion located closer to the first lens in the support surface and the first side surface;
• and
• a protruding portion connected to the main body portion and including a portion located closer to the second lens in the support surface, and
• at least a portion of the protruding portion is located inside the first hole portion.

A laser module comprising:

• a quantum cascade laser that includes:
• a substrate having a main surface and a back surface opposite to the main surface;
• a first clad layer provided on the main surface;
• an active layer provided on an opposite side of the first clad layer to the substrate;
• and
• a second clad layer provided on an opposite side of the active layer to the first clad layer,
• wherein the active layer has a first end surface and a second end surface facing each other in a second direction orthogonal to a first direction that corresponds to a stacking direction of the substrate, the first clad layer, the active layer, and the second clad layer,
• the first end surface constitutes a resonator for oscillating light of a first frequency and light of a second frequency, and
• the active layer generates a terahertz wave having a difference frequency between the first frequency and the second frequency;
• a diffraction grating unit that includes a movable diffraction grating constituting an external resonator for the light of the first frequency;
• a first lens disposed between the quantum cascade laser element and the movable diffraction grating and configured to transmit light emitted from the second end surface and light returning from the movable diffraction grating to the quantum cascade laser element;
• a second lens disposed at a position facing the first end surface and configured to transmit the terahertz wave emitted from the quantum cascade laser element;
• a first holder configured to hold the quantum cascade laser element;
• and
• a package that accommodates the quantum cascade laser element, the diffraction grating unit, the first lens, and the first holder and in which an optical path between a light incident surface of the second lens and the movable diffraction grating is disposed,
• wherein the first holder includes:
• a support surface on which the quantum cascade laser element is mounted;
• and
• a first side surface connected to the support surface and facing the first lens in the second direction,
• when viewed from a direction orthogonal to the first direction and the second direction, a first distance from an intersection point between the first side surface and the support surface to the second end surface along the second direction when a direction from the first lens toward the quantum cascade laser element along the second direction is a positive direction is smaller than a second distance between the intersection point and the first lens along the second direction,
• the laser module further comprising a second holder configured to hold the second lens,
• the second lens and the second holder are accommodated in the package,
• the package has a side wall facing the first end surface,
• the side wall is provided with a light exit window for transmitting light that is emitted from the first end surface and passes through the second lens,
• the second holder has a through hole penetrating in a third direction perpendicular to the side wall,
• the through hole includes:
• a first hole portion that opens toward the quantum cascade laser element;
• a second hole portion that opens toward the side wall, and that includes the first hole portion and is larger than the first hole portion when viewed from the third direction;
• and
• an annular counterbore surface connecting the first hole portion and the second hole portion and extending along a plane intersecting the second direction,
• an outer edge portion of the light incident surface of the second lens is inserted into the second hole portion from a side wall side and is fixed in surface contact with the counterbore surface,
• the first end surface is located inside the first hole portion, and
• the first holder further includes:
• a main body portion that includes a portion located closer to the first lens in the support surface and the first side surface;
• and
• a protruding portion connected to the main body portion and including a portion located closer to the second lens in the support surface, and
• at least a portion of the protruding portion is located inside the first hole portion.